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Iron(II) polypyridine complexes have the potential for numerous applications on a global scale, such as sensitizers, sensors, and molecular memory. The excited-state properties of these systems, particularly the intersystem crossing (ISC) rates, are sensitive to the choice of ligands and can be significantly altered depending on the coordination environment. We employ density functional theory and Smolyak's sparse grid interpolation algorithm to construct potential energy surfaces (PESs) for the photophysically relevant states (¹A, 3,5MC, and 1,3MLCT) of the [Fe(tpy)2]2+ (tpy = 2,2':6',2?-terpyridine) complex, with the goal of obtaining a deeper understanding of the ground- and excited-state electronic structure of this system. The three dimensions that define our adiabatic PESs consist of equatorial and axial metal-ligand bond length distortions and a terpyridine ligand "rocking angle", which has not previously been investigated. The intersection crossing seams and minimum energy crossing points (MECPs) between surfaces are also determined. Overall, we find that the PESs of all electronic excited states investigated are characterized by low-energy valleys along the tpy rocking-angle coordinate. This results in the presence of large low-energy areas around the MECPs on the intersection seams of different electronic states and indicates that inclusion of this third coordinate is crucial for an adequate description of the PESs and surface crossing seams of the [Fe(tpy)2]2+ complex. Finally, we suggest that tuning the energetics of the tpy ligand rocking motion could provide a way to control the ISC process in this complex. [ABSTRACT FROM AUTHOR]

Reactions of Hg(OTeF5)2 with excess amounts of NSF3 at 0 °C result in the formation of NSF3 adducts having the compositions [Hg(OTeF5)2·NSF3]∞ (1), [Hg(OTeF5)2·2NSF3]2 (2), and Hg3(OTeF5)6·4NSF3 (3). When the reactions are carried out at room temperature, oxygen/fluorine metatheses occur yielding the F2OSN- derivatives [Hg(OTeF5)(NSOF2)·NSF3]∞ (4) and [Hg3(OTeF5)5(NSOF2)·2NSF3]2 (5). The proposed reaction pathway leading to F2OSN- group formation occurs by nucleophilic attack by a F5TeO- group at the sulfur(VI) atom of NSF3, followed by TeF6 elimination. Tellurium hexafluoride formation was confirmed by 19F NMR spectroscopy. The NSF3 molecules are terminally N-coordinated to mercury, whereas the F2OSN- ligands are N-bridged to two mercury atoms. The compound series was characterized by low-temperature single-crystal X-ray diffraction and low-temperature Raman spectroscopy. Several structural motifs are observed within this structurally diverse series. These include the infinite chain structures of the related compounds, 1 and 4; 2, a dimeric structure which possesses an (HgOμ)2 ring at its core; 3, a structure based on a cage comprised of a (HgOμ)3 ring that is capped on each face by μ³-oxygen bridged F5TeO- groups; and 5, a dimeric structure possessing two distorted (Hg3O2N) rings that are formally derived from 3 by replacement of a F5TeO- group by a F2OSN- group in each ring. Quantum-chemical calculations were carried out to gain insight into the bonding of the μ³-oxygen bridged teflate groups observed in structure 3. Compounds 1–5 represent a novel class of neutral transition metal complexes with NSF3, providing the first examples of NSF3 coordination to mercury. Compounds 4 and 5 also provide the only examples of F2OSN- derivatives of mercury that have been characterized by single-crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

We report the photochemical generation and study of a family of water-soluble iron(IV)-oxo complexes supported by pentapyridine PY5Me2-X ligands (PY5Me2 = 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine; X = CF3, H, Me, or NMe2), in which the oxidative reactivity of these ferryl species correlates with the electronic properties of the axial pyridine ligand. Synthesis of a systematic series of [FeII(L)(PY5Me2-X)]2+ complexes, where L = CH3CN or H2O, and characterizations by several methods, including X-ray crystallography, cyclic voltammetry, and Mössbauer spectroscopy, show that increasing the electron-donating ability of the axial pyridine ligand tracks with less positive Fe(III)/Fe(II) reduction potentials and quadrupole splitting parameters. The FeII precursors are readily oxidized to their Fe(IV)-oxo counterparts using either chemical outer-sphere oxidants such as CAN (ceric ammonium nitrate) or flash-quench photochemical oxidation with [Ru(bpy)3]2+ as a photosensitizer and K2S2O8 as a quencher. The Fe(IV)-oxo complexes are capable of oxidizing the C-H bonds of alkane (4-ethylbenzenesulfonate) and alcohol (benzyl alcohol) substrates via hydrogen atom transfer (HAT) and an olefin (4-styrenesulfonate) substrate by oxygen atom transfer (OAT). The [FeIV(O)(PY5Me2-X)]2+ derivatives with electron-poor axial ligands show faster rates of HAT and OAT compared to their counterparts supported by electron-rich axial donors, but the magnitudes of these differences are relatively modest. [ABSTRACT FROM AUTHOR]

The effects of intrinsic cation disorder and electron-deficient substitution for La1-xSrxCo0.5Mn0.5O3-δ (LSCM, x = 0, 0.5, and 0.75) on oxygen vacancy formation, and their influence on the electrochemical properties, were revealed through a combination of computer simulation and experimental study. First-principles calculations were first performed and found that the tendency of the oxygen vacancy formation energy was Mn3+-O*-Mn4+ < Co2+-O*-Co3+ < Co2+-O*-Mn4+, meaning that antisite defects not only facilitate the formation of oxygen vacancy but introduce the mixed-valent transition-metal pairs for high electrical conductivity. Detailed partial density of states (PDOS) analysis for Mn on Co sites (MnCo) and Co on Mn sites (CoMn) indicate that Co2+ is prone to being Co3+ while Mn4+ is prone to being Mn3+ when they are on antisites, respectively. Also it was found that the holes introduced by Sr tend to enter the Co sublattice for x = 0.5 and then the O sublattice when x = 0.75, which further promotes oxygen vacancy formation, and these results are confirmed by both the calculated PDOS results and charge-density difference. On the basis of microscopic predictions, we intentionally synthesized a series of pure LSCM compounds and carried out comprehensive characterization. The crystal structures and their stability were characterized via powder X-ray Rietveld refinements and in situ high-temperature X-ray diffraction. X-ray photoelectron spectroscopy testified to the mixed oxidation states of Co2+/Co3+ and Mn3+/Mn4+. The thermal expansion coefficients were found to match the Ce0.8Sm0.2O2-δ electrolyte well. The electrical conductivities were about 41.4, 140.5, and 204.2 S cm-1 at doping levels of x = 0, 0.5, and 0.75, and the corresponding impedances were 0.041, 0.027, and 0.022 Ω cm² at 850 °C, respectively. All of the measured results testify that Sr-doped LaCo0.5Mn0.5O3 compounds are promising cathode materials for intermediate-temperature solid oxide fuel cells. [ABSTRACT FROM AUTHOR]

The interpretation of electron paramagnetic resonance spectra of polynuclear transition metal complexes in terms of individual contributions from each paramagnetic center can be greatly facilitated by the availability of theoretical methods that enable the reliable prediction of local spectroscopic parameters. In this work we report an approach that enables the application of multireference ab initio methods for the calculation of local zero field splitting tensors, one of the leading terms in the spin Hamiltonian for exchange-coupled systems of high nuclearity. The method referred to as local complete active space configuration interaction (L-CASCI) represents a multireference calculation with an active space composed of local orbitals of the center of interest. By successive permutation of the active space to include the localized orbitals corresponding to a particular center of the complex, all on-site parameters can be easily obtained at a high-level of theory with a corresponding low computational cost. Benchmark calculations on synthetic complexes confirm the validity of the approach. As an example of the applicability of the L-CASCI method to large systems, we determine the local anisotropy of the Mn(III) ion of the tetranuclear manganese cluster of photosystem II in both structural forms of its S2 state. [ABSTRACT FROM AUTHOR]

The electron densities in two analogous dimetallic transition metal compounds, namely, [M2(μ-OH2)(tBuCOO)4(tBuCOOH)2(C5H5N)2] (M = Co(1), Ni(2)), were determined from combined X-ray and neutron single-crystal diffraction at 100 K. Excellent correspondence between the thermal parameters from X- and N-derived atomic displacement parameters is found, indicating high-quality X-ray data and a successful separation of thermal and electronic effects. Topological analysis of electron densities derived from high-resolution X-ray diffraction, as well as density functional theory calculations, shows no direct metal-metal bonding in either compound, while the total energy density at the bond critical points suggests stronger metal-oxygen interactions for the Ni system, in correspondence with its shorter bond distances. The analysis also allows for estimation of the relative strength of binding of terminal and bridging ligands to the metals, showing that the bridging water molecule is more strongly bound than terminal carboxylic acid, but less so than bridging carboxylates. Recently, modeling of magnetic and spectroscopic data in both of these systems has shown weak ferromagnetic interactions between the metal atoms. Factors related to large zero-field splitting effects complicate the magnetic analysis in both compounds, albeit to a much greater degree in 1. The current results support the conclusion drawn from previous magnetic and spectroscopic measurements that there is no appreciable direct communication between metal centers. [ABSTRACT FROM AUTHOR]

Chlorine ligands in a variety of diamagnetic transition-metal (TM) complexes in common structural motifs were studied using 35Cl solid-state NMR (SSNMR), and insight into the origin of the observed 35Cl NMR parameters was gained through first-principles density functional theory (DFT) calculations. The WURST-CPMG pulse sequence and the variable-offset cumulative spectrum (VOCS) methods were used to acquire static 35Cl SSNMR powder patterns at both standard (9.4 T) and ultrahigh (21.1 T) magnetic field strengths, with the latter affording higher signal-to-noise ratios (S/N) and reduced experimental times (i.e., <1 h). Analytical simulations were performed to extract the 35Cl electric field gradient (EFG) tensor and chemical shift (CS) tensor parameters. It was found that the chlorine ligands in various bonding environments (i.e., bridging, terminal-axial, and terminal-equatorial) have drastically different 35Cl EFG tensor parameters, suggesting that 35Cl SSNMR is ideal for characterizing chlorine ligands in TM complexes. A detailed localized molecular orbital (LMO) analysis was completed for NbCl5. It was found that the contributions of individual molecular orbitals must be considered to fully explain the observed EFG parameters, thereby negating simple arguments based on comparison of bond lengths and angles. Finally, we discuss the application of 35Cl SSNMR for the structural characterization of WCl6 that has been grafted onto a silica support material. The resulting tungsten-chloride surface species is shown to be structurally distinct from the parent compound. [ABSTRACT FROM AUTHOR]

Two different neutral tridentate imine-donor pincer ligands interact with excess MCl2 (M = Co or Cu) to form compounds of the same stoichiometry, (LMC12)2̣MC12, where the assembling force is the electron richness of the terminal chlorides on the LMC12 unit. Finite aggregation occurs for M = Co, but for M = Cu, an infinite polymeric structure is adopted, all because MCl2 is bifunctional, which thus bridges multiple MCl units. The bis-pyrazolylpyridine ligand has two acidic NH protons, and both of these are involved in intramolecular hydrogen bonds. The generality of this Lewis acid aggregation is discussed. [ABSTRACT FROM AUTHOR]

A series of reports describing the syntheses and structures of [MCl2(diazadiene)] (M = Cr, Mo, W) complexes is reassessed in the context of known chemistry of low-valent Group VI metal complexes, crystallographic trends such as M--CI bond lengths and unit cell volumes, and calculated metal--ligand bond lengths. Crystallographic data and computational results are inconsistent with any of these species being second or third row transition metal complexes. A review of the crystallographic information files accompanying the [MCl2(diazadiene)] (M = Mo, W) published structures reveals that the metal atoms were inappropriately treated with partial site occupancy factors (0.775 for Mo; 0.4005 and 0.417 for W), the effect of which was to manifest lighter-element behavior and better refinement in accord with the metal atoms' correct identity. A deliberate synthesis and characterization by X-ray diflraction of [ZnCl2(MesdadMe)] (MesdadMe = l,4-bis(2,4,6-trimethylphenyl)-2,3-dimethyl-l,4-diaza-1,3-butadiene) are reported. Refinement of this structure with the same combination of second or third row metal and offsetting partial site occupancy is shown to provide final refinement statistics essentially the same as with the correct model employing M = Zn at site occupancy 1.00. Use of the published method for synthesis of [WCl2(diazadiene)] with MesdadMe and [WBr4(MeCN)2] in lieu of [WCl4MeCN2] is shown to produce [ZnBr2(MesdadMe)], which has also been characterized by X-ray diffraction. It is concluded that the unusual putative 12-electron [MCl2(diazadiene)] (M = Cr, Mo, W) complexes are in all cases the corresponding [ZnCl2(diazadiene)] complexes, Zn having been commonly employed as reducing agent in their synthesis. [ABSTRACT FROM AUTHOR]

A series of pseudosymmetrical structures of formula K10(M2OnF11-n)3X (M = V and Nb, n = 2, X = (F2Cl)1/3, Br, Br4/2,I4/2>; M = Mo, n = 4, X = CI, Br4/2, I4/2) illustrates generation of polar structures with the use of A- shaped basic building units (BBUs). For a compound to belong to a polar space group, dipole moments of individual species must be partially aligned. Incorporation of d° early transition metal polyhedral BBUs into structures is a common method to create polar structures, owing to the second-order Jahn--Teller distortion these polyhedra contain. Less attention has been spent examining how to align the polar moments of BBUs. To address alignment, we present a study on previously reported bimetallic BBUs and synthesized compounds K10(M2OnF11_n)3X. These materials differ in their (non)centrosymmetry despite chemical and structural similarities. The vanadium compounds are centrosymmetric (space groups P3ml or C2/m) while the niobium and molybdenum heterotypes are noncentrosymmetric (Pmn21). The difference in symmetry occurs owing to the presence of linear, bimetallic BBUs or A-shaped bimetallic BBUs and related packing effects. These A-shaped BBUs form as a consequence of the coordination environment around the bridging anion of the metal oxide fluoride BBUs. [ABSTRACT FROM AUTHOR]

Results indicate that the hydrolysis rates of the nitrosylruthenium complex under acidic conditions are similar to those occurring with the ruthenium(III) center under basic conditions. Furthermore, the degree of acetonitrile activation coordinated to the nitrosylruthenium complex is equal to that of acetonitrile coordinated to ruthenium(III)center.

The reduction of [(Cp'''Co)2(μ,η2:2-P2)2] (Cp''' = 1,2,4-tBu3C5H2) with the samarocenes, [(C5Me4R)2Sm(THF)n] (R = Me or n-propyl), gives [(Cp'''Co)2P4Sm(C5Me4R)2]. This is the first example of an intramolecular P-P coupling in a polyphosphide complex upon reduction of the transition metal. The formation of the P-P bond is not a result of the direct reduction of the phosphorus atoms but is induced by a rearrangement of the positive charges between the metal atoms. [ABSTRACT FROM AUTHOR]

Three platinum complexes with both a chloride anion and a chelated carboxylate as leaving groups were synthesized and spectrally characterized. In vitro cytotoxicity of complexes 1-3 was evaluated against human A549, HCT-116, MCF-7, and HepG-2 tumor cell lines. The results showed that all the compounds exhibited effective cytotoxicity against the tested cell lines, nearly comparable to those of cisplatin and oxaliplatin. Notably, the activity of complex 2 was about 2-fold better than that of oxaliplatin against the HCT-116 cell line. Flow cytometry analysis indicated that these complexes produced death of tumor cells through an apoptotic pathway. The DNA-binding properties of the platinum-based compounds were also studied by agarose gel electrophoresis. The kinetics study showed that the chloride anion departs from the Pt atom quickly, whereas the five and/or six-membered ring formed by coordination of N,O-donors and the metal ion is opened a little more slowly by the rupture of a Pt-O bond, which helps us to further understand the mechanism of action of the newly synthesized complexes with biomolecules. Furthermore, the reaction rate constants of complexes 1-3 were roughly the same. [ABSTRACT FROM AUTHOR]

The quaternary transition metal oxyselenide La202ZnSe2 has been shown to adopt a ZrCuSiAs-related structure with Zn2+ cations in a new ordered arrangement within the [ZnSe2]2- layers. This cation-ordered structure can be derived and described using the symmetry-adapted distortion mode approach. La2O2ZnSe2 is an direct gap semiconductor with an experimental optical band gap of 3.4(2) eV, consistent with electronic structure calculations. [ABSTRACT FROM AUTHOR]

Transition-metal complexes of the types [Re(CO)3Cl(NN)], [Re(CO)3py(NN)]+, and [Cu(PPh3)2(NN)]+, where NN = 4,4′-bis(5-phenyl-1,3,4-oxadiazol-2-yl)-2,2′-bipyridine (OX) and 4,4′-bis(N,N-diphenyl-4-[ethen-1-yl]-aniline)-2,2′-bipyridine (DPA), have been synthesized and characterized. Crystal structures for [Re(CO)3Cl(DPA)] and [Cu(PPh3)2(OX)]BF4 are presented. The crystal structure of the rhenium complex shows a trans arrangement of the ethylene groups, in agreement with density functional theory calculations. The structure of the copper complex displays the planar aromatic nature of the bpy–oxadiazole ligand. Density functional theory modeling of the complexes was supported by comparison of calculated and experimental normalized Raman spectra; the mean absolute deviations of the complexes were <10 cm-1. The Franck–Condon state was investigated using UV–vis and resonance Raman spectroscopic as well as density functional theory computational techniques. It was shown that the lowest energy absorption peaks are metal to ligand charge transfer and ligand-centered charge transfer for the oxadiazole- and diphenylaniline-substituted bipyridine ligands, respectively. The lowest energy excited states were characterized using transient emission and absorption spectroscopic techniques in conjunction with density functional theory calculations. These showed that the DPA complexes had ligand-centered nonemissive "dark" states with lifetimes ranging from 300 to 2000 ns. [ABSTRACT FROM AUTHOR]

A new hexanuclear cyclopentadienylnickel carbide cluster (NiCp)6(μ6-C) (1) was obtained through the thermolysis of the alkene complex [NiCp(CH3)(η2-CH2-CHC4H9)] (4). The X-ray molecular structure of 1 (monoclinic; P21/c; Ni-Ccarbide = 1.767(4)-2.109(4) Å) reveals a highly deformed octahedral arrangement of nickel atoms with two octahedron edges opened (Ni-Ni bonding distances = 2.410(1)-2.623(1) Å, Ni⋯Ni nonbonding distances = 3.107(2) and 3.108(2) Å). Cluster 1 is the first example of a homoleptic, cyclopentadienylnickel carbide cluster. Moreover, 13C-labeling studies proved that the carbido ligand in cluster 1 originated from the Ni-bound methyl group. This transformation requires a triple C-H bond activation in the methyl group, which has not been observed so far for late transition metal compounds. [ABSTRACT FROM AUTHOR]

The molybdenum(V) complex [Mo(O)Cl3dppe] [dppe = 1,2-bis(diphenylphosphino)ethane] is considered as a model system for a combined study of the electronic structure using UV/vis absorption and magnetic circular dichroism (MCD) spectroscopy. In order to determine the signs and MCD C-term intensities of the chlorido → molybdenum charge-transfer transitions, it is necessary to take the splitting of the excited doublet states into sing-doublet and trip-doublet states into account. While transitions to the sing-doublet states are electric-dipole-allowed, those to the trip-doublet states are electric-dipole-forbidden. As spin-orbit coupling within the manifold of sing-doublet states vanishes, configuration interaction between the sing-doublet and trip-doublet states is required to generate the MCD C-term intensity. The most prominent feature in the MCD spectrum of [Mo(O)Cl3dppe] is a "double pseudo-A term", which consists of two corresponding pseudo-A terms centered at 27000 and 32500 cm-1. These are assigned to the ligand-to-metal charge-transfer transitions from the pp orbitals of the equatorial chlorido ligands to the Mo dyz and dxz orbitals. On the basis of the theoretical expressions developed by Neese and Solomon (Inorg. Chem.1999, 38, 1847-1865), a general treatment of the MCD C-term intensity of these transitions is presented that explicitly considers the multideterminant character of the excited states. The individual MCD signs are determined from the corresponding transition densities derived from the calculated molecular orbitals of the title complex (BP86/LANL2DZ). [ABSTRACT FROM AUTHOR]

Reaction coordinates for oxo transfer from the substrates Me5NO, Me2SO, and Me3PO to the biologically relevant Mo(IV) bis-dithiolene complex [Mo(OMe)(mdt)2] where mdt 1,2-dimethyl-ethene-l,2-dithiolate(2-), and from Me2SO to the analogous W(IV) complex, have been calculated using density functional theory. In each case, the reaction first proceeds through a transition state (TS1) to an intermediate with substrate wealdy bound, followed by a second transition state (TS2) around which breaking of the substrate X-O bond begins. By analyzing the energetic contributions to each barrier, it is shown that the nature of the substrate and metal determines which transition state controls the rate-determining step of the reaction. [ABSTRACT FROM AUTHOR]

Skeletal Ni, produced by the selective leaching of Al from a Ni/Al alloy, has been successfully employed in the catalytic dehydrogenation of various amine—borane adducts. The combination of low cost and facile single-step synthesis make this system a potentially attractive alternative to the previously described precious metal and other first-row metal catalysts. The heterogeneous nature of the catalyst facilitates convenient product purification, and this is the first such system to be based on a first-row transition metal. Catalytic dehydrocoupling of Me2NH∙BH3 (1) and Et2NH∙BH3 (5) was demonstrated using 5 mol % skeletal Ni catalyst at 20 °C and produced [Me2N-BH2]2 (2) and [Et2N-BH2]2/Et2N-BH2 (6), respectively. The related adduct iPr2NH∙BH3 (7) was also dehydrogenated to afford iPr2N-BH2 (8) but with significant catalyst deactivation. Catalytic dehydrocoupling of MeNH2∙BH3 (9) was found to yield the cyclic triborazane [MeNH-BH2]3 (10) as the major product, whereas high molecular weight poly(methylaminoborane) [MeNH-BH2]n (11) (Mw = 78?000 Da, PDI = 1.52) was formed when stoichiometric quantities of Ni were used. Similar reactivity was also observed with NH3∙BH3 (12), which produced cyclic oligomers and insoluble polymers, [NH2—BH2]x (14), under catalytic and stoichiometric Ni loadings, respectively. Catalyst recycling was hindered by gradual poisoning. A study of possible catalyst poisons suggested that BH3 was the most likely surface poison, in line with previous work on colloidal Rh catalysts. Catalytic dehydrogenation of amine-borane adducts using skeletal Cu and Fe was also explored. Skeletal Cu was found to be a less active dehydrogenation catalyst for amine-borane adducts but also yielded poly(methylaminoborane) under stoichiometric conditions on reaction with MeNH2∙BH3 (9). Skeletal Fe was found to be completely inactive toward amine-borane dehydrogenation. [ABSTRACT FROM AUTHOR]

Single crystal synchrotron X-ray diffraction measurements have been carried out on [Nd(DMF)4(H2O)3(μ-CN)Fe(CN)5]·H2O (DMF = dimethyl-formamide), 1; [Y(DMF)4(H2O)3(μ-CN)Fe(CN)5]·H2O, 2; [Ce(DMF)4(H2O)3(μ-CN)Fe(CN)5]·H2O, 3; [Sm(DMF)4(H2O)3(μ-CN)Fe(CN)5]·H2O, 4; [Tb(DMF)4(H2O)3(μ-CN)Fe(CN)5]·H2O, 5; [Yb(DMF)4(H2O)3(μ-CN)Fe(CN)5]·H2O, 6; and [Nd(DMF)4(H2O)3(μ-CN)Co(CN)5]·H2O, 7, at 15(2) K with and without UV illumination of the crystals. Significant changes in unit cell parameters are observed for all of the iron-containing complexes, while compound 7 shows no response to UV illumination. These results are consistent with previous results and are furthermore reproduced by powder synchrotron X-ray diffraction for compounds 1 and 7. Photoexcited crystal structures have been determined for 1–6 from refinements of two-conformer models, and excited state occupancies in the range 80–94% are found. Significant bond length changes are observed for the Fe–ligand bonds (up to 0.06 Å), the cyano bonds (up to 0.02 Å), and the lanthanide–ligand bonds (up to 0.1 Å). On the contrary, powder X-ray diffraction on the simple compound K3Fe(CN)6, 8, upon UV illumination does not show any structural changes, suggesting that the photomagnetic effect requires the presence of both the transition metal and the lanthanide ion. Photomagnetic measurements show an increase in magnetization of the excited state of 1 of up to 3%, which is much diminished compared with previously published values of 45%. Furthermore, they show that the isostructural complex [La(DMF)4(H2O)3(μ-CN)Fe(CN)5]·H2O, 9, exhibits identical magnetic responses in the UV-induced excited crystal structure. [ABSTRACT FROM AUTHOR]

The trinuclear derivative Fe3(C8H8)3 was synthesized in 2009 by Lavallo and Grubbs via the reaction of Fe(C8H8)2 with a bulky heterocyclic carbene. This fascinating structure is the first example of a derivative of the well-known Fe3(CO)12 in which all 12 carbonyl groups have been replaced by hydrocarbon ligands. The density functional theory predicts a structure having a central Fe3 equilateral triangle with 2.9 Å Fe-Fe single bonded edges bridged by η5,η3-C8H8 ligands. This structure is close to the experimental structure, determined by X-ray crystallography. The related hypoelectronic MNi3(C8H8)3 derivatives (M = Cr, V, Ti) are predicted to have central scalene M3 triangles with edge lengths and Wiberg bond indices (WBIs) corresponding to one formal single M-M bond, one formal double M-M bond, and one formal triple M≡M bond. For Mn3(C8H8)3, both a doublet structure with one Mn-Mn double bond and two Mn-Mn single bonds in the Mn3 triangle, and a quartet structure with two Mn-Mn double bonds and one Mn-Mn single bond are predicted. The hyperelectronic derivatives MNi3(C8H8)3 have weaker direct M-M interactions in their M3 triangles, as indicated by both the M-M distances and the WBIs. Thus, NiNi3(C8H8)3 has bis(trihapto) η3,η3-C8H8 ligands bridging the edges of a central approximately equilateral Ni3 triangle with long Ni…Ni distances of ~3.7 Å. The WBIs indicate very little direct Ni-Ni bonding in this Ni3 triangle and thus a local nickel environment in the singlet Ni3(C8H8)3 similar to that observed for diallylnickel (η3-C3H5)2Ni. [ABSTRACT FROM AUTHOR]

When tested in solar cells, ruthenium polypyridinic dyes with extended π systems show an enhanced light-harvesting capacity that is not necessarily reflected by a high (collected electrons)/(absorbed photons) ratio. Provided that metal-to-ligand charge transfer bands, MLCT, are more effective, due to their directionality, than intraligand (IL) π-π* bands for the electron injection process in the solar cell, it seems important to explore and clarify the nature of the absorption bands present in these types of dyes. This article aims to elucidate if all the absorbed photons of these dyes are potentially useful in the generation of electric current. In other words, their potentiality as dyes must also be analyzed from the point of view of their contribution to the generation of excited states potentially useful for direct injection. Focusing on the assignment of the absorption bands and the nature of the emitting state, a systematic study for a series of ruthenium complexes with 4,4′-distyryl-2,2′-dipyridine (LH) and 4,4′-bis[p-(dimethylamino)-α-styryl]-2,2′-bipyridine (LNMe2) "chromophoric" ligands was undertaken. The observed experimental results were complemented with TDDFT calculations to elucidate the nature of the absorption bands, and a theoretical model was proposed to predict the available energy that could be injected from a singlet or a triplet excited state. For the series studied, the results indicate that the percentage of MLCT character to the anchored ligand for the lower energy absorption band follows the order [Ru(deebpy)2(LNMe2)](PF6)2 > [Ru(deebpy)2(LH)](PF6)2 > [Ru(deebpy)(LH)2](PF6)2, where deebpy is 4,4′-bis(ethoxycarbonyl)-2,2′-bipyridine, predicting that, at least from this point of view, their efficiency as dyes should follow the same trend. [ABSTRACT FROM AUTHOR]

Several transition metal compounds are effective antitumor drugs whose biological activity can be attributed to their ability to bind deoxyribonucleic acid (DNA). In this study, DNA-binding experiments reveal that changing one bridging ligand on compounds with the general formula Rh2(μ-L)(HNOCCF3)3 alters the rate of DNA-binding by greater than 100-fold with μ-L = trifluoroacetate acetate > trifluoroacetamidate. These three dirhodium compounds are isolated as the major products of the reaction between Rh2(OOCCH3)4 and trifluoroacetamide in either refluxing chlorobenzene or molten trifluoroacetamide and have been characterized by NMR and LC/MS. By using 15N-enriched trifluoroacetamide, NMR spectroscopy was used to assign the cis-(2,1) orientations of Rh2(μ-L)(HNOCCF3)3 compounds where μ-L = trifluoroacetate or acetate. This is the first report of Rh2(OOCCF3)(HNOCCF3)3, a novel compound that may play a significant role in the biological and/or catalytic activity of compound mixtures commonly isolated as “Rh2(HNOCCF3)4”. [ABSTRACT FROM AUTHOR]

The thermally induced hysteretic spin transition (ST) that occurs in the polymeric chain compound [Fe(NH2trz)3](NO3)2 (1) above room temperature (Tc↑ = 347 K, Tc↓ = 314 K) has been tracked by 57Fe Mssbauer spectroscopy, SQUID magnetometry, differential scanning calorimetry (DSC), and X-ray powder diffraction (XPRD) at variable temperatures. From the XRPD pattern indexation, an orthorhombic primitive cell was observed with the following cell parameters: a = 11.83(2) Å, b = 9.72(1) Å, c = 6.361(9) Å at 298 K (low-spin state) and a = 14.37(2) Å, b = 9.61(4) Å, c = 6.76(4) Å at 380 K (high-spin state). The enthalpy and entropy variation associated to the ST of 1, have been evaluated by DSC as ΔH = 23(1) kJ mol-1 and ΔS = 69.6(1) J mol-1 K-1. These thermodynamic data were used within a two-level Ising like model for the statistical analysis of First Order Reversal Curve (FORC) diagram that was recorded for 1, in the cooling mode. Strong intramolecular cooperative effects are witnessed by the derived interaction parameter of J = 496 K. The crystal structure of [Cu(NH2trz)3](NO3)2·H2O (2) was obtained thanks to high quality single crystals prepared by slow evaporation after hydrothermal pretreatment. The catena poly[μ-tris(4-amino-1,2,4-triazole-N1,N2) copper(II)] dinitrate monohydrate (2) crystallizes in the monoclinic space group C2/c, with a = 16.635(6) Å, b = 13.223(4) Å, c = 7.805(3) Å, β = 102.56(3)°, Z = 4. Complex 2 is a 1D infinite chain containing triple N1,N2-1,2,4-triazole bridges with an intra-chain distance of Cu⋯Cu = 3.903(1) Å. A dense H-bonding network with the nitrate counteranion involved in intra-chain and inter-chain interactions is observed. Such a supramolecular network could be at the origin of the unusually large hysteresis loop displayed by 1 (ΔT ∼ 33 K), as a result of an efficient propagation of elastic interactions through the network. This hypothesis is strengthened by the crystal structure of 2 and by the absence of crystallographic phase transition for 1 over the whole temperature range of investigation as shown by XRPD. [ABSTRACT FROM AUTHOR]

Density functional theory in conjunction with nonequilibrium Green's functions has been used to explore charge transport through the cobalt-based extended metal atom chain, Co3(dpa)4(NCS)2. The isolated molecule has a doublet ground state, and the singly occupied s nonbonding orbital proves to be the dominant transport channel, providing spin filtering efficiencies in excess of 90%. The metal chain differs from typical organic conductors in that the p orbitals that form the contact with the gold electrode are orthogonal to the transport channel. As a result, the rehybridization of these p levels by the applied electric field has only a minor impact on the current, allowing spin filtering to persist even at biases in excess of 1 V. [ABSTRACT FROM AUTHOR]

Treatment of ortho-carborane, n-butyl lithium, sulfur, and CpCo(CO)I2 with differing ratios led to four new compounds [(CpCoS2C2B10H10)(CpCoSC2B10H11)(SC4H9)] (3), [(CpCo)2S2(S2C2B10H10) (SC2B10H10)(SC4H9)] (4), [(CpCo)2Co(SC4H9)6]+[Co(S2C2B10H10)2]- (5), and [(CpCo)2Co(SC2B10H11)(SC4H9)5]+[Co(S2C2B10H10)2]- (6). Compound 3 contains a rhombic Co2(μ2-S)2 core and can be considered as an adduct of the two 16e half-sandwich monomers CpCo(S2C2B10H10) (1) and CpCo(SC4H9)(SC2B10H11). Compound 4 is a trinuclear complex containing a cuboidal [Co3(μ3-S)2(μ-S)2] core, and one cobalt atom is coordinated by six sulfur atoms in a distorted octahedral geometry. Compound 5 consists of a linear-type trinuclear cobalt(III) monocation bridged by six n-butyl thiolato units and a square-planar cobalt(III) monoanion [Co(S2C2B10H10)2]-. However, in 6, one ortho-carborane monothiolato ligand [SC2B10H11]- has replaced one n-butyl thiolato ligand in 5. This leads to a nonlinear arrangement of the three cobalt atoms in the cation and the nonplanar [Co(S2C2B10H10)2]- anion in 6. Interestingly, the treatment of the 16e half-sandwich CpCo(S2C2B10H10) (1) by [N(n-Bu)4]Br afforded the ionic compound 7, [N(n-Bu)4]+[Co(S2C2B10H10)2]-, containing a square-planar anion. [ABSTRACT FROM AUTHOR]

The reaction of [AuCl(tht)] (tht = tetrahydrothiophene) with SbMesnPh3-n (n = 3 (1), 2 (2), 1 (3)) produces the 1:1 adducts [AuCl(SbMesnPh3-n)] (n = 3 (4), 2 (5), 1 (6)), with a Sb-Au-Cl environment, regardless of the molar ratio used (1:1 to 1:4). Addition of the same stibines to [Au(tht)2]ClO4 (molar ratio 1:1 to 1:4) results in isolation of the 1:2 adducts [Au(SbMesnPh3-n)2]ClO4 (n = 3 (7), 2 (10)), containing linear Sb-Au-Sb fragments, or the 1:3 adduct [Au(SbMesPh2)3]ClO4 (11), with a quasi trigonal planar AuSb3 core. The same 1:2 cations are produced when [Au(tht)2]CF3SO3 is reacted with 1 or following a rearrangement process when 4 is treated with AgSbF6, that is, [Au(SbMes3)2]X (X = CF3SO3 (8), SbF6 (9)). The compounds were characterized by spectroscopic methods, and the molecular structures of 2-4, 7, 8∙2CDCl3, 9, and 11 were established by single-crystal X-ray diffraction. Theoretical calculations were carried out on model systems of type ER3 and [Au(ER3)n]+ (E = P or Sb; R = Ph or Mes; n = 2, 3, or 4) to gain insight into the bonding nature of SbR3 ligands in homoleptic gold-stibine adducts, in comparison with phosphine-gold(I) compounds. Steric effects govern the coordination of stibines with mesityl substituents. A preference for higher coordination numbers is observed for SbPh3 when compared with PPh3 and experimentally observed C-Sb-C and Sb-C structural distortions of stibines upon coordination are reproduced theoretically. [ABSTRACT FROM AUTHOR]

We report the structure, electrochemistry, and isomerization kinetics for [Ru(bpy)(biq)(OSO)](PF6), where bpy is 2,2′-bipyridine, biq is 2,2′-biquinoline, and OSO is 2-methylsulfinylbenzoate. UV-visible and infrared data are suggestive of intramolecular S→O and O→S isomerization of the sulfoxide. Cyclic voltammetry reveals evidence for isomerization triggered by oxidation and reduction. Of particular note is the variation of the S→O isomerization rate constant in different solvents. The rates were found to be 3.2 (±0.4) s-1 in propylene carbonate, 0.80 (±0.03) s-1 in acetonitrile, and 0.26 (±0.01) s-1 in dichloromethane. [ABSTRACT FROM AUTHOR]

Middle and late transition metal imido complexes (which may also be viewed as metal—nitrene adducts) are rather rare, especially for square-pyramidal and octahedral coordination geometries. However, an iron(ll) porphyrin aminonitrene adduct, denoted here as Fe(Por)(NN), has been known for almost a quarter of a century. Unlike the corresponding S= 1 oxene and S = 0 carbene adducts, Fe(Por)(NN) exhibits an S = 2 ground slate. DFT calculations reported herein provide a molecular orbital description of this unusual species as well as a rationale for its S = 2 ground stale. The electronic configuration of Fe(Por)(NN) may be described as dπ2dxy1dze1dxe-yedπ'1, where the z direction corresponds to the Fe—NN axis. The stability and double occupancy of one of the dπ orbitals may be attributed to a π-backbonding interaction with the N-N π* orbital. The weak a-donor ability of the aminonitrene ligand results in a relatively low-energy dze orbital and an overall d orbital splitting pattern that engenders a high-spin ground state. [ABSTRACT FROM AUTHOR]

Unlike the case with other divalent transition metal M[TCNO]2(H2O)2 (M=Fe, Co, Ni) analogues, the etectrochemically induced solid-solid phase interconversion of TCNQ microcrystals (TCNO=7,7,8,8-tetracyanoquinodimethane) to Mn[TCNQ]2(H2O)2 occurs via Iwo vollammeltically distinct, lime dependenl processes that generate Ihe coordination polymer in nanofiber or rod-like morphologies. Careful manipulation of the voltammetric scan rate, electrolysis time, Mn2+(aq) concentration, and the method of electrode modification with solid TCNQ allows selective generation of either morphology. Detailed ox situ spectroscopic (IR, Raman), scanning electron microscopy (SEM), and X-ray powder diffraction (XRD) charactetization cleady establish that differences in the electrochemically synthesized Mn-TCNQ material are confined to morphology. Generation of the nanofiber fom't is proposed to take place rapidly via formation and reduction of a Mn'stabilized anionic dimer intermediate, [(Mn2+)(TCNQ-TCNQ)2•-, formed as a result of radical-substrate coupling between TCNQ•- and neutral TCNQ, accompanied by ingress of Mn2+ ions from the aqueous solution at the triple phase TCNQ/electrode/electrolyte boundary. In contrast, formation of the nanorod form is much slower and is postulated to arise from disproportionation of the [(Mn2+)(TCNQ-TCNQ)•-2] intermediate. Thus, identification of the time dependent pathways via the solid-solid state electrochemical approach allows the crystal size of the Mn[TCNQJ2(H2O)2 material to be tuned and provides new mechanistic insights into the formation of different morphologies. [ABSTRACT FROM AUTHOR]

Pyridine-2,6-dimethanethiolate and pyridine-2,6-dithiocarboxylate form sparingly soluble Ni[supII] pincer complexes formulated as [Ni(pdmt)][sub2] and Ni(pdtc)][sub2], respectively, with Ni-(μ[sub2]-S)-Ni bridges. In acetonitrile reaction systems, the latter undergoes the facile bridge cleavage reactions [Ni(pdtc)][sub2] + 2L[sup0,-]→2[Ni(pdtc)L][sup0,-] with an extensive set of nucleophiles to afford planar mononuclear products with L[sup-] = halide, CN, Me[sub3]SiO[sup-], RS[sup-] and L[sup0] = Et[sub3]P and a N-heterocyclic carbene. [Ni(pdmt)][sub2] is considerably less reactive toward bridge disruption. Cleavage products support several reactions of interest leading to other mononuclear species and to di and trinuclear complexes. [Ni(pdtc)(OSiMe[sub3])][sup1-] deprotonates acetonitrile and acetone to form [Ni(pdtc)(CH[sub2]R)][sup1-] (R=CN, COMe). Reaction of [Ni(pdtc)SEt][sup1-] with Fe[supII] yields the thiolate-bridged dimer ([Ni(pdtc)][sub2](SEt))[sup1-]. Refluxing an acetonitrile solution of [Ni(pctd)SH][sup1-] in air results in trinuclear [Ni(pdtc)][sub3]S][sup2-] containing the rare unsupported Ni[sub3](μ[sub3]-S) bridge core. Reaction of [Ni(pdtc)CN][sup1-] with [Fe(Me[sub6]tren)(OTf)][sup1+] forms the complex [Ni(pdtc)CNFe(Me[sub6]tren)][sup1+], the only example of a single Ni—CN— Fe bridge within a molecule. Structures of the various types of reaction products are presented. This work demonstrates the potential utility of bridge cleavage of polynuclear Ni[supII] thiolates, an extensive family of compounds to produce mononuclear products. [ABSTRACT FROM AUTHOR]

The kinetico-mechanistic study of the formation of discrete tri- and tetranuclear mixed-valence cyano-bridged (Co[supIII])[sub2]/Fe[supII] and (Co[supIII])[sub3]/Fe[supII] complexes has been carried out from their already described parent dinuclear Co[supIII]/Fe[supII] and mononuclear Co[supIII] complexes. Different Co[supIII] encapsulating units have been used in order to tune both the redox potential on the monoand dinuclear complexes and the lability of the mononuclear building blocks. The importance of outer-sphere precursor complex formation involving the oppositely charged reactants has been established by experiments conducted at high ionic strength where electrostatic effects are nullified. The influence of the pH is also crucial, and this has been linked to the pH dependence of the precursor Co[supIII] redox potentials in terms of enabling a redox-assisted association (at low pH) between the ferricyanide analogue and the labile CoU partner. A new asymmetric Co[supIII]L/Fe[supII]/Co[supIII]L' complex has been fully characterized, and a series of putative (Co[supIII]L)[sub2]/Fe[supII]/C[supIII]L' and (Co[supIII]L)[sub3]/Fe[supII] forms have been spectroscopically detected. A comparison with the mechanistic reaction pathways established for the formation of the parent dinuclear Co[supIII]/Fe[supII] complexes indicates that an important tuning of the direct substitution and redox-catalyzed mechanism is applicable. For the formation of the trinuclear complexes, only in the most favorable conditions is a redox-assisted sequence observed. The rate and activation parameters for the reactions have been determined and are indicative of an essential outer-sphere precursor formation. Similarly, for reactions where redox-assisted mechanisms are unfavorable, only direct substitution processes have been found to be applicable, with their rate coefficients and activation parameters also agreeing with the expectations, once an outersphere precursor complex is formed. Formation of the tetranuclear (Co[supIII]L)[sub3]/Fe complexes has only been detected on decomposition of the parent trinuclear (Co[supIII]L)[sub2]/Fe[supII] complexes following reduction to their Co[supII] form. The overall processes seem to be based on the outer-sphere association between the respective building blocks in such a way that both unfavorable redox potentials and Lewis basicities are overcome. [ABSTRACT FROM AUTHOR]

A collection of new quaternary intermetallic compounds with a cubic, stuffed BaHg11 structure type has been synthesized by the combination of a divalent rare earth or alkaline earth metal R, an early transition metal T, and gold in an excess of molten aluminum. Structural characterization of these R3Au6+xAl26T compounds by powder and single crystal X-ray diffraction indicates that the unit cell varies with the radii of the early transition metal I and the rare earth/alkaline earth R as expected. The element T (where T = group 4, 5, 6, and 7 element) appears to be responsible for the stabilization of up to 43 different members of the R3Au6+xAl26T family of compounds. Varying amounts of disorder and trends in partial occupancies of the Au stuffed site—the site that is vacant in the parent compound BaHg11—are also indicated by the diffraction studies of this family of compounds. Magnetic susceptibility data reveals that the transition metal atoms in these materials do not possess local magnetic moments. For the magnetic rare earth containing materials, the europium compounds undergo a ferromagnetic transition at 10 K, and the ytterbium analogues show mixed valent behavior. Band structure calculations also support a mixed valent state for Yb in these compounds. [ABSTRACT FROM AUTHOR]

The electronic structures of the molecules (tBuO)3MN (M = Cr, Mo, W) have been investigated with gas phase photoelectron spectroscopy and density functional calculations. It is found that the alkoxide orbitals mix strongly with the MN triple bond orbitals and contribute substantially to the valence electronic structure. The first ionization of (tBuO)3CN is from an orbital of a2(C3r) symmetry that is oxygen based and contains no metal or nitrogen character by symmetry. In contrast, the first ionizations of the molybdenum and tungsten analogues are from orbitals of a1 and e symmetry that derive from the highest occupied MN σ and π orbitals mixed with the appropriate symmetry combinations of the oxygen p orbitals. In this a1 orbital, the oxygen p orbitals mix, with the highest occupied MN orbital of a symmetry. This mixing reduces the, metal character, consequently reducing the metal—nitrogen overlap interaction in this orbital. From computational modeling, the polarity of the MN bond increases down the group such that WN has the highest charge separation. In addition to investigation of the effects of the metals, the electronic influences of substitution at the alkoxide ligands have been examined for the molecules (RO)3MoN (R = C(CH3)2H, C(CH3)3, and C(CH3)2CF3). The introduction of CF3 groups stabilizes the molecular orbital energies and ,increases the measured ionization energies, but does not alter the overall electronic structure. The bonding characteristics of the (tBuO)3MN series are compared with those of organic nitriles. [ABSTRACT FROM AUTHOR]

This article describes the linking propensity of the sulfite encapsulated polyoxovanadate (POV) anion, [As8V14O42(SO3)]6-, with aqua-lanthanide complex cations [Ln(H2O)6]3+ in a controlled wet synthesis resulting in a series of organic free metal-oxide-based materials [{Ln(H2O)6}2As8V14O42(SO3)]·8H2O, Ln = La3+ (1), Sm3+ (2), and Ce3+ (3). The title compounds have been characterized by elemental analyses, IR, diffuse reflectance, electron paramagnetic resonance, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), and single-crystal X-ray diffraction studies. All three compounds crystallize in the monoclinic space group P21/n. Crystal data for 1: a = 13.4839(7), b = 12.3388(6), c = 18.3572(10) Å, β = 108.2570 (10)°, V = 2900.4(3) Å3. Crystal data for 2: a = 13.4156(3), b = 12.2588(3), c = 18.2501(4) Å, ² = 108.049(3)°, V = 2853.8(10) Å3. Crystal data for 3: a = 13.4934(3), b = 12.3983(3), c = 18.3992(4) Å, ² = 108.025 (3), V = 2927.0(10) Å3. Crystal structure shows that each cluster is surrounded by six [Ln(H2O)6]3+ complex cations, and each [Ln(H2O)6]3+ cation is coordinated to three surrounding POV cluster anions. The electron spin resonance spectra of compounds 1-3 show a typical single line (g = 1.9671 for 1, g = 1.9669 for 2, and g = 1.9704 for 3), characteristic for a V4+ (d4) ion; in addition, a supplementary signal appears for compound 2 at g = 5.9238 due to the presence of the Sm3+ (f5) ion. All vanadium atoms exit in +4 oxidation states that have been confirmed by bond valence sum calculations. Variable-temperature magnetic studies for all three compounds 1-3 are performed and are discussed in terms of antiferromagnetic coupling interactions, giving importance to linking/assembling the {V14} cluster anions. TGA/mass analyses of compounds 1-3 (linked system) have been compared with that of the starting precursor [NH4]6[As8V14O42(SO3)] (discrete building unit). Interestingly, the evolution of SO2 gas takes place for the discrete cluster compound [NH4]6[As8V14O42(SO3)] in a temperature range of 480-520 °C with the decomposition of the POV cluster anion, whereas the same evolution occurs at 520-580 °C for compounds 1-3. These comparative TGA/mass studies help to understand how the organic free linker elevates the thermal stability of the sulfite encapsulated POV cluster anion in going from a discrete cluster anion to the linked system (molecule to material). It has also been demonstrated that the stability of the sulfite anion increases to a greater extent when it is included in the cluster cage. The powder XRD studies of compounds 1-3 confirm that these are isostructural materials and provide information about the phase purity. [ABSTRACT FROM AUTHOR]

Four hexanuclear molybdenum chloride cluster complexes containing terminal thiolate ligands have been synthesized and fully characterized. (Bu4N)2[Mo6Cl5(SEt)6] was prepared by reacting Na2[Mo6Cl5(OMe)6] with an excess of ethanethiol in refluxing tetrahydrofuran. (PPN)2[Mo6Cl8(SBu)6], (Bu4N)2[Mo6Cl8(SBn)6], and (Bu4N)2[Mo6Cl8(SNC8H6)6] (C8H6NS- = 3-indolylthiolate) were subsequently prepared in the reaction of [Mo6Cl8(SEt)6]2- with an excess of HSR (R = Bu, Bn or 3-indolyl). Single crystal X-ray diffraction analyses were performed on two of these complexes: (PPN)2[Mo6Cl8(SEt)6]. Et2O, crystallizes in the triclinic space group P1 with a = 12.3894(11), b = 13.7651(12), c = 15.0974(13), α = 103.975(2), β = 99.690(2), γ = 98.062(2), and Z = 1; (PPh3Me)2[Mo6Cl8(SBn)6] · 2NO2CH3, also crystallizes in the P1 space group with a = 12.1574(16), b = 13.4441(17), c = 14.2132(18), α = 89.654(2), β = 88.365(2), γ = 71.179(2), and Z = 1. Our studies demonstrate that [Mo6Cl8(SEt)6]2- displays luminescent properties and that the same complex undergoes substitution reactions with different thiols, as well as reaction with electrophilic reagents such as Mel. [ABSTRACT FROM AUTHOR]

We present a theoretical study of the ground and the lowest triplet excited states of the tris-(1,4,5,8-tetraazaphenanthrene) ruthenium complex [Ru(tap)3]2+. Density functional theory (DFT) was used to obtain the relaxed geometries and emission energies (Δ-SCF), whereas time-dependent DFT (TD-DFT) was used to compute the absorption spectrum. Our calculations have revealed the presence of three low-lying excited-state minima, which may be relevant in the photophysical/photochemical properties of this complex. Two minima with similar energies correspond to the MLCT ³A2 and MLCT ³B metal-to-ligand charge-transfer states, the first one corresponding to a D3 structure, whereas the second is a slightly localized D3 species. The third and lowest one corresponds to the metal-centered MC ³A state and displays a pronounced D3 distortion. We have examined for the first time the localized character of the excitation in the computed MLCT states: In particular, we have evaluated the pseudorotation barrier between the Jahn-Teller D3 MLCT ³B minima in the moat around the D3 conical intersection. We have shown that the complex should be viewed as a delocalized [Ru3+(tap-1/3)3]2+ complex in the lowest MLCT states, in agreement with subpicosecond interligand electron transfer observed by femtosecond transient absorption anisotropy study. Upper-bound estimates of the MLCT→MC (3 kcal/mol) and MC→MLCT (10 kcal/mol) activation energy barriers obtained from potential energy profiles in vacuum corroborate the high photoinstability of the MLCT states of the [Ru(tap)3]2+ complex. [ABSTRACT FROM AUTHOR]

A series of calix[4]arene-based binuclear platinum(II) complexes, Pt2LCl2 (1, L = 5,11,17,23-tetra-tert-butyl-25,27-di[methoxy(4-phenyl)-(C∧N∧N)]-26,28-dihydroxycalix[4]arene, HC∧N∧N = 6-phenyl-2,2′-bipyridine), [Pt2L(μ-dppCn)]-(ClO4)2 (dppCn = bis(diphenylphosphino)-methane (2, n = 1), -ethane (3, n = 2), -propane (4, n = 3), and [Pt2L(PPh3)2](ClO4)2 (5), have been designed and synthesized in this work. Spectroscopic investigation demonstrates that p-tert-calix[4]arene is capable of assembling the two square-planar [(C∧N∧N)Pt(II)] units in a face-to-face manner, simultaneously suppressing intermolecular aggregation and increasing the solubility of the studied complexes. Facile replacement of the chloride ligand in 1 by the strongly σ-donating ancillary phosphine ligands affords binuclear platinum(II) complexes with improved photophysical properties. All of the complexes are emissive both in the fluid! glassy solution and in the solid state, except for 1 in the solid state at room temperature. Moreover, the absorption and emission energies of the complexes are sensitive to the ancillary ligands. Varying the tethered phosphine auxiliaries from dppm (2) and dppe (3) to dppp (4) and PPh3 (5) modulates the intramolecular metal-metal (Pt ⋯ Pt) and ligand-ligand (π-π) distances, thereby leading to a switch of ³MMLCT and excimeric ³(ππ*) excited states to a common ³MLCT excited state. [ABSTRACT FROM AUTHOR]

Three novel 3D pillared-layer heterometallic lanthanide-transition-metal (hetero-Ln-TM) compounds, namely, Ln2Cu7I6(ina)7(H2O)6 · H2 [ina = isonicotinic acid; Ln = Ce (1), Sm (2)] and Er4(OH)4Cu5I4(ina)6(na)(2,5-pdc) · 0.3H2O (3; na = nicotinic acid, 2,5-pdc 2,5-pyridinedicarboxylic acid), have been obtained by incorporating different metal clusters as building blocks under hydrothermal conditions. Compounds 1 and 2 are isostructural and consist of two distinct building units of dimeric [Ln2(ina)6] cores and inorganic 2D [Cu8I7]nn+ layers based on the [Cu3I3] and [Cu4I3]+ clusters. Compound 3 is constructed from decanuclear [Cu10I8]2+ clusters and inorganic 1D [Er4(OH)4]n8n+ cluster chain-based layers, which represent the first example of a 3D hetero-Ln-TM constructed by the combination of two distinct types of metal cluster units of a 1D [Er4(OH)4]n8n+ cluster polymer and a transition-metal cluster. It is interesting that decarboxylation occurred in the ortho position and 2,5-pdc2- was partially transformed into na under hydrothermal conditions. Compounds 1-3 represent good examples of using different metal cluster units to construct fascinating 3D hetero-Ln-TM frameworks. [ABSTRACT FROM AUTHOR]

Four polymorphs of IrI(CO)2(OC(CH3)CHC(CH3)N(p-tol)) have been characterized by single crystal X-ray crystallography. While all contain the same molecular unit with no significant structural variations within the molecules, all show different degrees of metallophilic interactions between the planar molecules. Three of these (the amber, the pale yellow, and the orange forms) are stable at room temperature, while the fourth, the L. T. orange form, is only obtained by cooling the orange polymorph. At 77 K, the amber, pale yellow, and L. T. orange polymorphs show intense luminescence. The variations in the luminescence among the polymorphs are considered in the context of the structural differences between them and the nature of the metallophilic interactions between the iridium centers. These results demonstrate how subtle variations in molecular organization can affect the physical properties of planar d8 transition metal compounds, which are an important class of lumiphores. [ABSTRACT FROM AUTHOR]

Treatment of Ru(PPh3)3Cl2 with K(tpip) (tpip- = [N(Ph2PO)2]-) afforded Ru(tpip)(PPh3)2Cl (1), which reacted with 4-t-Bu-C6H4CN, SO2(g), and NH3(g) to give Ru(tpip)(PPh3)2Cl(4-t-BuC6H4CN) (2), Ru(tpip)(PPh3)2Cl(SO2) (3), and fac-[Ru(NH3)3(PPh3)2Cl][tpip] (4), respectively. Reaction of [Ru(CO)2Cl2]x with K(tpip) in refluxing tetrahydrofuran (THF) led to isolation of the K/Ru bimetallic compound K2Ru2(tpip)4(CO)4Cl2 (5). Photolysis of cis-Ru(tpip)2(NO)Cl in MeCN and wet CH2Cl2 afforded cis-Ru(tpip)2(MeCN)Cl (6) and cis-Ru(tpip)2(H2O)Cl (7), respectively. Refluxing 6 in neat THF yielded Ru(tpip)2(THF)Cl (8). Treatment of Ru(CHR)Cl2(PCy3)2 (Cy = cyclohexyl) with [Ag(tpip)]4 afforded cis-Ru(tpip)2(CHR)(PCy3) [R = Ph (9), OEt (10)]. Complex 9 is capable of catalyzing oxidation of alcohols and olefins with N-methylmorpholine N-oxide and iodosylbenzene, respectively. The crystal structures of 2-7 and 9 were determined. [ABSTRACT FROM AUTHOR]

A phenomenally high molar extinction coefficient heteroleptic ruthenium(ll) complex [Ru(4,4'-carboxylic acid-2,2'- (DCSC1 3) was synthesized by incorporating donor-acceptor ligands. The absorption spectrum of the DCSC13 sensitizer is dominated by metal-to-ligand charge-transfer transitions (MLCT) in the visible region, with absorption maxima appearing at 442 and 554 nm. The lowest MLCT absorption bands are red-shifted, and the molar extinction coefficients of these bands are significantly higher at 72 100 and 30 600 M1 cm1, respectively, when compared to those of the analogous [Ru(4,4'-carboxylic acid-2,2'-bipyridine)(4,4'-dimethyl-2,2'-bipyridine)(NCS)21 (N820)' sensitizer. The DCSC13 complex, when anchored on nanocrystalline Ti02 films, exhibited increased short-circuit photocurrent and consequent power-conversion efficiency when compared with the N820 sensitizer. [ABSTRACT FROM AUTHOR]

Three new vanadate compounds of the formulas (C2N2H10)VO(OH)4 (I), (NH4)3(C3N2H5)V4O10 (II), and V(OH)3· 0.97H2O (III) have been synthesized by a solvothermal method and characterized by IR spectroscopy, elemental analysis, and thermogravimetric analysis. The crystal structures of the above three vanadates have been established by single-crystal X-ray diffraction. Compound I crystallizes as tetragonal, space group P4/mmm, with a = 9.0465- (11) Å, c 3.9897(10) Å, V = 326.51(10) Å3, and Z = 2. Compound II crystallizes as orthorhombic, space group Immm, with a = 3.6012(10) Å, b = 11.312(4) Å, c = 15.050(4) A, V= 613.1(3) Å3, and Z = 2. Compound III crystallizes as cubic, space group Fd3¯m, with a = 10.4252(17) Å, V = 1133.1(3) Å3, and Z = 16. Structural analyses reveal a one-dimensional beeline-chained structure, which consists of V06 octahedra in I. Compound II possesses a two-dimensional V-O-layered structure formed by VO5 square pyramids; protonated imidazole and remaining NH4+ cations are inserted between the layers. The three-dimensional open framework of III with the pyrochlore type consists of V12 and V4 secondary building units by using VO6 octahedra as building units. [ABSTRACT FROM AUTHOR]

The ruthenium(II)-triphos acetato complex [RuCI(OAc)(κ3-triphos)] (triphos = (PPh2CH2)3CMe) has been found to be an active catalyst precursor for the hydrogenation of 1-alkenes under relatively mild conditions (5-50 bar H2, 50 °C). In contrast to related triphenyiphosphine complexes, [RuCl(OAc)(κ3-triphos)] is much less air sensitive and high catalytic activities were achieved when catalyst samples were prepared without exclusion of air or moisture. Substitution of the acetato ligand can be effected by treatment of acid, affording [Ru2(μ-Cl)3(κ3-triphos)2]Cl and [RuCI(κ3-triphos)]2(BF4)2 with aqueous HCI and [Et2OH]BF4, respectively, or by heating with dmpm in the presence of [NH4]PF6, resulting in formation of IRuCl(κ2-dmpm)(κ3-triphos)]PF6 (dmpm = PMe2CH2PMe2). A hydride complex, [RuHCI(κ3-triphos)], formed by acetato-mediated heterolytic cleavage of dihydrogen is proposed as the active catalytic species. An inner-sphere, monohydride mechanism is suggested for the catalytic cycle, with chloro and triphos ligands playing a spectator role. These mechanistic proposals are consistent with reactivity studies carried out on [RuCI(OAc)(κ3-triphos)] and [RuH(OAc)(κ3-triphos)] and supported by a computational analysis. The solid-state structures of [RuCI(OAc)(κ3-triphos)], [RuCl(κ3-triphos)]2(BF4)2, and [RuCl(κ2-dmpm)(κ3-triphos)]PF6 have been established by X-ray diffraction. [ABSTRACT FROM AUTHOR]

Olive-green cobalt(III) complexes having the general formula Co4O4(O2CMe)4L4 (1) where L = py (1a), 4-Mepy (1b), 4-Etpy (1c), and 4-CNpy (1d) have been prepared by the H2O2 oxidation of a mixture of Co2+, MeCO2-, and pyridine or 4-substituted pyridines in a 1:2:1 molar ratio in methanol. Spectroscopic and X-ray crystallographic studies show that these complexes contain a tetrameric cubane-like core [Co4(μ3-O)4]4+ where the four cobalt atoms form an approximate tetrahedron with edge lengths of ∼2.75 Å. Each cobalt in the crystallographically determined structure of Co4(μ3-O)4(μ-O2CMe)4L4 in 1a·NaClO4·3.5H2O and 1b·3H2O is hexacoordinate. Infrared spectra of the complexes show characteristic bands near 700, 635, and 580 cm-1 due to the central cubane-like core. ¹H NMR spectra of the complexes show that the dissolved species are essentially diamagnetic and also that the complexes maintain their integrity in solution. UV-vis spectra of the green solutions have been interpreted in terms of ligand-field and charge-transfer bands. The electrochemical behavior of the complexes studied by cyclic and differential pulse voltammetric techniques indicates that the [(CoIII)4(μ3-O)4]4+ core present in the complexes undergoes a reversible one-electron oxidation to the [(CoIII)3CoIV/(μ3-O)4]5+ core with an E1/2 value below 1 V. This suggests that these complexes of cobalt may be suitable as catalysts for the oxidation of organic compounds. Preliminary investigations indicate that la has a role to play in the cobalt-catalyzed aerobic oxidation of neat ethylbenzene and p-xylene. [ABSTRACT FROM AUTHOR]

A novel Iris heteroleptic dipyridophenazine complex of ruthenium(II), [{Ru(phen)(dppz)(bpy'-his) }{Ru(NH3)5}]5+, containing a covalently tethered ruthenium pentammine quencher coordinated through a bridging histidine has been synthesized and characterized spectroscopically and biochemically in a DNA environment and in organic solvent. Steady-state and time-resolved luminescence measurements indicate that the tethered Ru complex is quenched relative to the parent complexes [Ru(phen)(dppz)(bpy')]2+ and [Ru(phen)(dppz)(bpy'-his)]2+ in DNA and acetonitrile, consistent with intramolecular photoinduced electron transfer. Intercalated into guanine-containing DNA, [{Ru(phen)(dppz)(bpy'-his)}{Ru(NH3)5}]5+, upon excitation and intramolecular quenching, is capable of injecting charge into the duplex based upon the EPR detection of guanine radicals. DNA-mediated charge transport is also indicated using a kinetically fast cyclopropylamine-substituted base as an electron hole trap. Guanine damage is not observed, however, in measurements using the guanine radical as the kinetically slower hole trap, indicating that back electron-transfer reactions are competitive with guanine oxidation. Moreover, transient absorption measurements reveal a novel photophysical reaction pathway for [{Ru(phen)(dppz)(bpy'-his)}{Ru(NH3)5}]5+ in the presence of DNA that is competitive with the intramolecular flash-quench process. These results illustrate the remarkably rich redox chemistry that can occur within a bimolecular ruthenium complex intercalated in duplex DNA. [ABSTRACT FROM AUTHOR]

We report the synthesis and crystal structures of two transition metal-based coordination polymers comprising ligand molecules not included in the original reaction mixtures but instead formed in situ during hydrothermal treatment. Zinc meso-iminodisuccinate hydrate (I), Zn2(C8H7NO8)·0.57H2O, formed from zinc acetate and L-aspartic acid, and tetraaquanickel(II) 5,10-dioxo-5,10-dihydro-4,9-dioxa-pyrene-2,7-dicarboxylate (II), Ni(H2O)4(C16H4O8), formed from nickel acetate and 5-hydroxyisophthalic acid. We show that the formation of I takes place via a fumaric acid intermediate, while the formation of II requires the formation of a new C—C bond. The structure of I consists of weakly interacting sheets, while the structure of II consists of strongly hydrogen-bonded chains. Crystal data: for I, P21/n (14), a = 10.073 Å, b = 9.894 Å, c = 12.053 Å, β = 105.605°, V= 1156.87(13) Å13, Z= 4; for II, P1 (2), a = 5.011 Å, b = 6.526 Å, c = 12.305 Å, β = 76.8680, β = 84.988°, γ = 87.619°, V = 390.3(4) Å3, z = 1. [ABSTRACT FROM AUTHOR]

The effect of a counteranion on chiral recognition inducing conglomerate crystallization of a cobalt(III) complex is reported. An achiral tripodal ligand involving three imidazole groups, tris{[2-{(imidazol-4-yl)methylidene}amino]-ethyl}amine (H3L), was prepared by condensation of tris(2-aminoethyl)amine and 4-formylimidazole in a 1:3 mole ratio. The reaction of H3L and trans-[CoIIICl2(py)4]+ afforded the chiral (Δ or Λ) [CoIII(H3L)]3+ complex. The formally hemideprotonated complexes [CoIII(H1.5L)]X1.5·nH2O (where X Cl, Br, I, BF4, CIO4, or PF6) were synthesized by controlled deprotonation of the uncoordinated imidazole NH groups of [Co(H3L)]3+. In crystals of the hemideprotonated complex, two components, [Co(H3L)]3+ and [Co(L)], with the same absolute configuration are linked by imidazole-imidazolate hydrogen bonds to form an extended homochiral 2D sheet structure, which is composed of a hexanuclear unit with a trigonal void. There are two ways of stacking the sheets: One is via homochiral stacking, and the other is via heterochiral stacking. When the size of the counterion is small (i.e., X = Cl, Br, I, or BF4), adjacent homochiral sheets with the same chirality are stacked to form a homochiral crystal (conglomerate). With large anions (i.e., ClO4- and PF6-), a homochiral sheet consisting of Δ enantiomers and a sheet consisting of Λ enantiomers are stacked alternately to give a heterochiral crystal (a racemic crystal). Optically active Λ-[Co(H1.5L)](CIO4)1.5·H2O was synthesized from Λ-[Co(H3L)]3+, and the crystal structure was compared to that of the racemic complex. There are two conflicting factors governing the crystal structure: the skeletal density; the size of the channels. The 2D sheets are more closely packed in the homochiral crystal than in the heterochiral crystal. However, the channels, where the counterions are accommodated, are smaller in the homochiral crystal, and the steric congestion between the anions increases with increasing anion size. The heterochiral crystal has a flexible, zigzag channel structure, and the size of the channels can increase to accommodate larger anions. Thus, complexes with large anions (i.e., CIO4- and PF6-) preferentially form heterochiral crystals rather than homochiral crystals. [ABSTRACT FROM AUTHOR]

X-ray and NMR experiments were performed with simple chitosan models based on glucosamine monosaccharides and disaccharides to understand the binding properties and structures of the complexes formed between this polysaccharide and platinum(II) metals. Subjection of the glucosamine derivatives with [PdCl2(PhCN)2] provided transdiamine complexes which upon further treatment with excess (NH4)PF6 generated complexes possessing two 5-membered chelate rings involving the C2-amine and the C3-hydroxyl group of the two individual glucosamine units. [ABSTRACT FROM AUTHOR]

The synthesis of a new bioinspired dinucleating ligand scaffold based on a bridging pyrazolate with appended bis[2-(1-methylimidazolyl)methyl}aminomethyl chelate arms is reported. This ligand forms very stable copper complexes, and a series of different species is present in solution depending on the pH. lnterconversions between these solution species are tracked and characterized spectroscopically, and X-ray crystallographic structures of three distinct complexes that correspond to the species present in solution from acidic to basic pH have been determined. Overall, this provides a comprehensive picture of the copper coordination chemistry of the new ligand system. Alterations in the protonation state are accompanied by changes in nuclearity and pyrazolate binding, which cause pronounced changes in color and magnetic properties. Antiferromagnetic coupling between the copper-(II) ions is switched on or off depending on the pyrazole binding mode. [ABSTRACT FROM AUTHOR]