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Four-coordinate distorted tetrahedral bis(2-iminopyrrolyl)cobalt(ii) complexes behave as Single-Ion Magnets (SIMs) in the absence of an external magnetic field.

Metal complexes of 1,2-diamidobenzenes have been long studied because of their intriguing redox properties and electronic structures. We present here a series of such complexes with 1,2-bis(sulfonamido)benzene ligands to probe the utility of these ligands for generating a large zero-field splitting (ZFS, D) in metal complexes that possibly act as single-ion magnets. To this end, we have synthesized a series of homoleptic ate complexes of the form (X)n[M{bis(sulfonamido)benzene}2] (n equals 4 minus the oxidation state of the metal), where M (Fe/Co/Ni), X [K+/(K-18-c-6)+/(HNEt3)+, with 18-c-6 = 18-crown ether 6], and the substituents (methyl and tolyl) on the ligand [bmsab = 1,2-bis(methanesulfonamido)benzene; btsab = 1,2-bis(toluenesulfonamido)benzene] were varied to analyze their effect on the ZFS, possible single-ion-magnet properties, and redox behavior of these metal complexes. A combination of X-ray crystallography, (spectro)electrochemistry, superconducting quantum interference device magnetometry, high-frequency electron paramagnetic resonance spectroscopy, and Mossbauer spectroscopy was used to investigate the electronic/geometric structures of these complexes and the aforementioned properties. These investigations show that the cobalt(II) complexes display very high negative D values in the range of -100 to -130 cm-1, and the nickel(II) complexes display very high positive D values of 76 and 58 cm-1. In addition, the cobalt(II) complexes shows barriers of 200-260 cm-1 and slow relaxation of the magnetization in the absence of an external magnetic field, underscoring the robustness of this class of complexes. The iron(II) complex exhibits a D value of -3.29 cm-1 and can be chemically oxidized to an iron(III) complex that has D = -1.96 cm-1. These findings clearly show that bis(sulfonamido)benzenes are ideally suited to stabilize ate complexes, to generate very high ZFSs at the metal centers with single-ion-magnet properties, and to induce exclusive oxidation at the metal center (for iron) despite the presence of ligands that are potentially noninnocent. Our results therefore substantially enhance the scope for this class of redox-active ligands.

Here we explore the electronic structure of the diiron complex [(dppf)Fe(CO)3]0/+ [10/+; dppf = 1,1'-bis(diphenylphosphino)ferrocene] in two oxidation states by an advanced multitechnique experimental approach. A combination of magnetic circular dichroism, X-ray absorption and emission, high-frequency electron paramagnetic resonance (EPR), and Mossbauer spectroscopies is used to establish that oxidation of 10 occurs on the carbonyl iron ion, resulting in a low-spin iron(I) ion. It is shown that an unequivocal result is obtained by combining several methods. Compound 1+ displays slow spin dynamics, which is used here to study its geometric structure by means of pulsed EPR methods. Surprisingly, these data show an association of the tetrakis[3,5-bis(trifluoromethylphenyl)]borate counterion with 1+.

The fine-tuning of intermolecular or intramolecular non-covalent interactions (NCIs) and thus the precise synthesis of metal complexes in which the spin states can be controlled by NCIs remains challenging, even though several such complexes have been intensively studied. In this regard, we present mononuclear cobalt(II) and iron(II) complexes with "click"-derived tripodal ligands that contain fluorinated benzyl substituents in the secondary coordination sphere. The complexes were co-crystallized with different solvent molecules to decipher the effect of the crystallized solvents on NCIs, and on the spin state of the metal ion. Additionally, the fluorine-specific interactions in the secondary coordination sphere were examined. We present a first structure-property correlation between the nature of interaction of the (per)fluorinated aromatic substituents on the ligand periphery, and the spin state of the metal complexes. In particular, the TF5TA containing ligand show interesting stacking motifs depending on the used solvent, and these interactions have an influence on the spin state of the cobalt(II) complexes. Furthermore, the iron(II) complex thereof, Fe(TF5TA)2(BF4)2·2EtOH displays spin crossover (SCO).

We have successfully prepared and structurally characterized a family of butterfly-like [Co2 IIILn2 III] complexes where all magnetic properties are due to the Ln(iii) ions. The complexes with Ln = Tb(1), Dy(2), Ho(3), Er(4) and Yb(5) are iso-structural. An exception is the complex with Ln = Gd(6) which strings in a one dimensional chain. The structural similarity together with the high tendency of the crystallites to align under an applied magnetic field allowed an overall DC magnetic data treatment to extract phenomenological crystal field parameters and hence to determine the ground state multiplet energy level splitting. The Dy(iii) member is the only one showing slow relaxation of magnetization under zero DC applied field, while all the others need a small DC applied field. Fil: Funes, Víctor Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina Fil: Carrella, Luca. University Mainz. Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg; Alemania Fil: Rechkemmer, Yvonne. Universität Stuttgart; Alemania Fil: Van Slageren, Joris. Universität Stuttgart; Alemania Fil: Rentschler, Eva. University Mainz. Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg; Alemania Fil: Alborés, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina

The azido ligand is widely used in coordination chemistry both as a ligand and as a metal-bound reactant. Its role as a bridge for magnetic exchange coupling has attracted a lot of attention in polynuclear metal complexes. However, only a very limited number of complexes are known in which a single azide anion, particularly in the μ1,1-mode, is the only unsupported connection between two metal centers. We present here a series of copper(II)–azido complexes with amine anchored, triazole-based tripodal ligands containing varying substituents. In the mononuclear copper–azido complexes there is only a negligible effect of these substituents on the structure of the metal complexes. However, the substituents seem to play a decisive role in the type and formation of the dinuclear complexes. Using the tripodal ligand TBTA with flexible benzyl substituents resulted in a rare example of an unsupported and solely μ1,1-azido-bridged dinuclear complex. The use of the TDTA ligand with 2,6-diisopropylphenyl moieties as rigid and sterically demanding substituents resulted in the formation of a scarce example of a solely μ1,4-tetrazolato-bridged dinuclear complex by in situ cycloaddition between the azide and solvent nitrile. This observation of a reaction of unactivated aliphatic nitrile with the azide anion at room temperature is very unusual. The isolation and characterization (by means of X-ray diffraction) of intermediates allows for mechanistic insights into the cycloaddition reaction. The isolated bridges in both dinuclear complexes render them ideal model compounds for the investigation of the magnetic exchange mediated by these ligands usually employed in polynuclear complexes and frameworks together with additional bridging ligands. Magnetic measurements and broken-symmetry DFT calculations were used to shed light on the magnetic exchange revealing weak and moderate antiferromagnetic exchange for the azide and tetrazolate, respectively.

The static and dynamic magnetic properties of a pentacoordinate [Co(phen)(DMSO)Cl2] compound (phen = 1,10'-phenanthroline, DMSO = dimethyl sulfoxide) were thoroughly studied by experimental (SQUID magnetometry and HF-EPR spectroscopy) and theoretical methods (DFT and CASSCF calculations). It has been found from temperature/field-dependent magnetization measurements that the studied compound possesses a large and negative magnetic anisotropy (D = -17(1) cm(-1)) with large rhombicity (E/D = 0.24(5)), and these experimental results are in agreement with ab initio calculations (D = -17.7 cm(-1), E/D = 0.31). Interdoublet resonances were not observed in the HF-EPR measurements, but the large rhombicity was confirmed (DEPR = -17.7 cm(-1) (fixed from CASSCF calculations), E/DEPR = 0.33). A frequency dependent out-of-phase susceptibility signal was observed only in a non-zero static magnetic field (B = 0.1 T) and the following parameters of slow-relaxation of magnetisation were derived from the experimental data: either the energy of spin reversal barrier, Ueff = 10.4 K, and the relaxation time, τ0 = 5.69 × 10(-9) s using the Debye model, or Ueff = 21.4-40.3 K and τ0 = 0.248-58.3 × 10(-9) based on a simplified model.

The gadolinium (Gd) member of a new type of heteropolytungstates that contain one lanthanide and two transition metal ions in a triangular arrangement is reported. The compound NaK6Gd0.33 [((VO)2Gd(H2O)4K2(H2O)2(Na)(H2O)2)(α-B-AsW9O33)2]·24H2O (1) was prepared from acidified aqueous solutions of Na2WO4·2H2O, As2O3 and VOSO4·5H2O to which Gd3+ ions were added. The single crystal X-ray structure analysis (monoclinic, space group P21/m) shows that the anion consists of two [α-B-AsIIIW9O33]9− trilacunary Keggin-type units linked by two VO2+, one Gd3+ as well as weakly by two K+ and one Na+ ions, resulting in a sandwich-type structure with idealized C 2v symmetry. The problem of positioning crystal lattice and special polyoxometalate sites with different cations is discussed also in connection with supramolecular chemistry aspects and as an option for further research. A fit of the magnetic susceptibility yielded exchange coupling constants of J VV = −2.55 cm−1 (anti-ferromagnetic) between the vanadium ions and J GdV = 0.6 cm−1 (ferromagnetic) between the Gd and each of the two vanadium ions. The complete magnetochemical analysis also revealed a partial occupancy of the Na+ sites in the counter-cation–water system by Gd3+ ions (0.33 Gd3+ ions in total).

We report three dinuclear cobalt(II) complexes, [Co(L)Cl2]2 (L = bpy, mbpy, and dmpbt), that are bridged solely by chloride ions. High-field electron paramagnetic resonance and magnetometric measurements were applied to investigate the magnetic intramolecular Co–Co interactions. Simulation results based on the multispin model reveal that the complexes are weakly ferromagnetically coupled and that the isotropic exchange coupling constants differ slightly for the three complexes. Moreover, the competing effects of zero-field splitting and magnetic coupling on the temperature-dependent magnetic susceptibility were analyzed.

The azide anion is widely used as a ligand in coordination chemistry. Despite its ubiquitous presence, controlled synthesis of azido complexes remains a challenging task. Making use of click-derived tripodal ligands, we present here various coordination motifs of the azido ligands, the formation of which appears to be controlled by the peripheral substituents on the tripodal ligands with otherwise identical structure of the coordination moieties. Thus, the flexible benzyl substituents on the tripodal ligand TBTA led to the formation of the first example of an unsupported and solely μ1,1-azido-bridged dicobalt(II) complex. The more rigid phenyl substituents on the TPTA ligand deliver an unsupported and solely μ1,3-azido-bridged dicobalt(II) complex. Bulky diisopropylphenyl substituents on the TDTA ligand deliver a doubly μ1,1-azido-bridged dicobalt(II) complex. Intriguingly, the mononuclear copper(II) complex [Cu(TBTA)N3]+ is an excellent synthon for generating mixed dinuclear complexes of the form [(TBTA)...

A synthetic protocol to synthesize 2-bromobenzo-1,3,2-dithiaboroles in one step from easily accessible benzene bis(isopropyl thioether)s has been developed. The reaction is remarkably specific in converting substrates with two adjacent (i)PrS moieties while leaving isolated thioether functions and other functional groups intact. On the basis of the spectroscopic detection or isolation of reaction intermediates, a mechanistic explanation involving a neighbor-group-assisted dealkylation as a key step is proposed. The resulting products featuring one or two dithiaborole units were isolated in good yields and fully characterized. Subsequent methanolysis, which was carried out either as a separate reaction step or in the manner of a one-pot reaction, gave rise to functionally substituted benzenedithiols. The feasibility of a methylphosphoryl-substituted benzenedithiol to act as a dianionic S,S-chelating ligand was demonstrated with the formation of paramagnetic Ni(III) and Co(III) complexes. Selective reduction of the phosphoryl group afforded a rare example of a phosphino dithiol which was shown to act as a monoanionic P,S-bidentate ligand toward Pd(II). All complexes were characterized by spectral data and X-ray diffraction studies, and the paramagnetic ones also by superconducting quantum interference device magnetometry.

The newly obtained complexes [NiII8LnIII6(Piv)16(teaH)6(OCH3)2(CO3)2(H2O)2] Ln = Gd, Dy, show a remarkable μ5-carbonate bridged octanuclear planar {Ni4Ln4} core further capped with embedded {Ni3Ln} cubane motifs to afford a rod shaped nano-sized molecule of about 1.2 × 2.8 nm. Unusual MCE behaviour has been found due to multiple low lying excited states arising from competing ferromagnetic and anti-ferromagnetic Ni-Ni and Ni-Ln exchange interactions. Fil: Guarda, Eliana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Bader, Katharina. Universität Stuttgart; Alemania Fil: Van Slageren, Joris. Universität Stuttgart; Alemania Fil: Alborés, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina

The reaction of the hexacyanometalates K3[M(1)(CN)6] (M(1) = Cr(III), Fe(III), Co(III)) with the bispidine complexes [M(2)(L(1))(X)](n+) and [M(2)(L(2))(X)](n+) (M(2) = Mn(II), Ni(II), Cu(II); L(1) = 3-methyl-9-oxo-2,4-di-(2-pyridyl)-7-(2-pyridylmethyl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylic acid dimethyl ester; L(2) = 3-methyl-9-oxo-7-(2-pyridylmethyl)-2,4-di-(2-quinolyl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylic acid dimethyl ester; X = anion or solvent) in water-methanol mixtures affords trinuclear complexes with cis- or trans-arrangement of the bispidine-capped divalent metal centers around the hexacyanometalate. X-ray structural analyses of five members of this family of complexes (cis-Fe[CuL(2)]2, trans-Fe[CuL(1)]2, cis-Co[CuL(2)]2, trans-Cr[MnL(1)]2, trans-Fe[MnL(1)]2) and the magnetic data of the entire series are reported. The magnetic data of the cyanide bridged, ferromagnetically coupled cis- and trans-Fe[ML]2 compounds (M = Ni(II), Cu(II)) with S = 3/2 (Cu(II)) and S = 5/2 (Ni(II)) ground states are analyzed with an extended Heisenberg Hamiltonian which accounts for anisotropy and zero-field splitting, and the data of the Cu(II) systems, for which structures are available, are thoroughly analyzed in terms of an orbital-dependent Heisenberg Hamiltonian, in which both spin-orbit coupling and low-symmetry ligand fields are taken into account. It is shown that the absence of single-molecule magnetic behavior in all spin clusters reported here is due to a large angular distortion of the [Fe(CN)6](3-) center and the concomitant quenching of orbital angular momentum of the Fe(III) ((2)T2g) ground state.

The generation of molecular platforms, the properties of which can be influenced by a variety of external perturbations, is an important goal in the field of functional molecular materials. We present here the synthesis of a new quinonoid ligand platform containing an [O,O,O,N] donor set. The ligand is derived from a chloranilic acid core by using the [NR] (nitrogen atom with a substituent R) for [O] isoelectronic substitution. Mononuclear FeII and CoII complexes have been synthesized with this new ligand. Results obtained from single crystal X-ray crystallography, NMR spectroscopy, (spectro)electrochemistry, SQUID magnetometry, multi-frequency EPR spectroscopy and FIR spectroscopy are used to elucidate the electronic and geometric structures of the complexes. Furthermore, we show here that the spin state of the FeII complex can be influenced by temperature, pressure and light and the CoII complex displays redox-induced spin-state switching. Bistability is observed in the solid-state as well as in solution for the FeII complex. The new ligand presented here, owing to the [NR] group present in it, will likely have more adaptability while investigating switching phenomena compared to its [O,O,O,O] analogues. Thus, such classes of ligands as well as the results obtained on the reversible changes in physical properties of the metal complexes are likely to contribute to the generation of multifunctional molecular materials., Dalton Transactions, 45 (20), ISSN:1477-9226, ISSN:1477-9234

The zero-field splitting parameters of two non-integer spin state single molecule magnets were determined using frequency domain magnetic resonance spectroscopy: D = −0.454 ± 0.004 cm −1 , B 4 0 = ( + 1 . 01 ± 0 . 05 ) × 10 - 5 cm - 1 for [Mn 12 ] − , and D = −0.247 ± 0.005 cm −1 , B 4 0 = ( + 4 . 6 ± 0 . 1 ) × 10 - 6 cm - 1 for [Mn 9 ]. The linewidth of the magnetic resonance lines is determined by distributions in the zero-field splitting parameters in the case of [Mn 9 ], leading to a Gaussian lineshape. Interestingly, the resonance line is homogeneously broadened in the case of [Mn 12 ] − , which is one of the few examples in single molecule magnetism. This means that the linewidth is determined by the excited spin state lifetime, which can be calculated to be 50–58 ps depending on the temperature.

A new family of tetranuclear Ni complexes [Ni(4)(ROH)(4)L(4)] (H(2)L = salicylidene-2-ethanolamine; R = Me (1) or Et (2)) has been synthesized and studied. Complexes 1 and 2 possess a [Ni(4)O(4)] core comprising a distorted cubane arrangement. Magnetic susceptibility and inelastic neutron scattering studies indicate a combination of ferromagnetic and antiferromagnetic pairwise exchange interactions between the four Ni(II) centers, resulting in an S = 4 spin ground state. Magnetization measurements reveal an easy-axis-type magnetic anisotropy with D approximately -0.93 cm(-)(1) for both complexes. Despite the large magnetic anisotropy, no slow relaxation of the magnetization is observed down to 40 mK. To determine the origin of the low-temperature magnetic behavior, the magnetic anisotropy of complex 1 was probed in detail using inelastic neutron scattering and frequency domain magnetic resonance spectroscopy. The spectroscopic studies confirm the easy-axis-type anisotropy and indicate strong transverse interactions. These lead to rapid quantum tunneling of the magnetization, explaining the unexpected absence of slow magnetization relaxation for complex 1.

Crystallographically characterised 3,6-bis(2′-pyridyl)pyridazine (L) forms complexes with {(acac)2Ru} or {(bpy)2Ru2+} via one pyridyl-N/pyridazyl-N chelate site in mononuclear RuII complexes (acac)2Ru(L), 1, and [(bpy)2Ru(L)](ClO4)2, [3](ClO4)2. Coordination of a second metal complex fragment is accompanied by deprotonation at the pyridazyl-C5 carbon {L → (L − H+)−} to yield cyclometallated, asymmetrically bridged dinuclear complexes [(acac)2RuIII(μ-L − H+)RuIII(acac)2](ClO4), [2](ClO4), and [(bpy)2RuII(μ-L − H+)RuII(bpy)2](ClO4)3, [4](ClO4)3. The different electronic characteristics of the co-ligands, σ donating acac− and π accepting bpy, cause a wide variation in metal redox potentials which facilitates the isolation of the diruthenium(III) form in [2](ClO4) with antiferromagnetically coupled RuIII centres (J = −11.5 cm−1) and of a luminescent diruthenium(II) species in [4](ClO4)3. The electrogenerated mixed-valent RuIIRuIII states 2 and [4]4+ with comproportionation constants Kc > 108 are assumed to be localised with the RuIII ion bonded via the negatively charged pyridyl-N/pyridazyl-C5 chelate site of the bridging (L − H+)− ligand. In spectroelectrochemical experiments they show similar intervalence charge transfer bands of moderate intensity around 1300 nm and comparable g anisotropies (g1 − g3 ≈ 0.5) in the EPR spectra. However, the individual g tensor components are distinctly higher for the π acceptor ligated system [4]4+, signifying stabilised metal d orbitals.

High-frequency (190 GHz) EPR spectra are reported, that were recorded on an exchange coupled, trimeric copper cluster, octachlorodiadeniniumtricopper(II). The lines in the rhombic spectra shift as a function of temperature. This can be traced to the presence of two close lying spin doublet states, with different g tensors, that interconvert quite rapidly. Therefore, the lines observed in the spectrum have the Boltzmann weighted average of the two g values. The interesting observation is that signals due to the excited spin doublet are observed. This means that the interconversion rate is of the same order of magnitude as the Electron Paramagnetic Resonance experiment. Previous experiments at X-band frequency (9 GHz) could only ascertain that the interconversion rate was faster than that frequency.

The electronic absorption and luminescence properties of electron-rich organometallic platinum(II) complexes with aromatic α-diimine ligands [(α-diimine)PtR2] (R = alkyl, alkynyl, Ph or Mes, Mes = 2,4,6-trimethylphenyl) were examined. The crystal and molecular structures of [(bpy)PtMe2], [(tap)PtPh2] and [(tmphen)PtMes2] were determined from single-crystal XRD and discussed in view of intermolecular interactions that influence the emission behaviour. The combination of theoretical calculations (DFT) and spectroscopic techniques (absorption and emission) revealed the character of electronic transitions and excited states. In particular they showed that the co-ligand involvement in the frontier orbitals is small for R = Me, but large in case of R = alkynyl, Ph or Mes. Depending on the chelate ligand and its substitution pattern, the emission efficiencies of the complexes cover a wide range from strong emission in fluid solution at ambient temperature to very weak emission in rigid matrices (glasses) at low temperatures with no emission at ambient temperature. The emission lifetimes, determined at low temperature in solvent glasses, mainly depend on the chelate ligand and not on the co-ligands. The emission quantum yields of the complexes in solution at room temperatures are much larger for R = Mes than for R = Ph or Me. The emission bands for the complexes with unsaturated co-ligands show slight structuring at low temperatures in contrast to the alkyl-substituted ones. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The photochemical reactivity, photophysical properties and redox behavior of the complexes trans , cis -[Ru(X)(X′)(CO) 2 (α-diimine)] and their derivatives are strongly dependent on the complex geometry, the nature and electronic properties of the α-diimine ligand and, most importantly, on the axial ligands X and X′ (alkyl, halide, phosphine, donor solvent, etc.). This paper deals mainly with comparison of reduction pathways for several different types of the trans , cis -[Ru(X)(X′)(CO) 2 (α-diimine)] complexes, also presenting some new results in this field. An equally important goal has been the comparison and discussion of the photo- and redox reactivity of these complexes from the viewpoint of the frontier orbitals involved and character of the RuX/X′ bonding.

This paper reviews the photochemical PtC bond homolysis reactions of metalcarbon bonded platinum compounds. Three types of complexes are considered: [Pt(R) 2 (COD)], [Pt(R) 2 (α-diimine)] and [Pt(Me) 4 (α-diimine)]. This photoreactivity originates in the involvement of the σ-bonded co-ligands in low-lying excited states. This involvement was proved by time-dependent density-functional theory (TD DFT) calculations and resonance Raman (rR) spectroscopy. In the case of the platinum(II) complexes, the contribution of the co-ligand to the high-lying filled orbitals increases with increased σ-donor strength of this ligand. Concurrently, the photoreactivity increases dramatically in the case of the [Pt(R) 2 (COD)] complexes. The corresponding α-diimine analogues are much less reactive due to the smaller co-ligand participation in high-lying filled orbitals. The platinum(IV) complexes [Pt(Me) 4 (α-diimine)] are very photoreactive, due to the fact that the HOMO has almost exclusively σ(C ax PtC ax ) character.

The multiple emission from [W(CO) 4 (phen)] and [W(CO) 4 (tmp)] (phen=1,10-phenanthroline, tmp=3,4,7,8-tetramethyl-1,10-phenanthroline) was studied by nanosecond time-resolved emission spectroscopy, measured from a 2-MeTHF glass at 80 K. Two emission bands were observed for each complex. The low-energy emission decays with double-exponential kinetics: τ ≅150 and 487 ns for [W(CO) 4 (phen)]; 612 and 2684 ns for [W(CO) 4 (tmp)]. The high-energy emission decays much faster, τ ≤40 ns. The energies and characters of the singlet and triplet excited states were calculated for both complexes, using time-dependent density functional theory and were used to interpret the emission spectra. The low-energy emission band was attributed to the radiative decay of two unequilibrated W→phen/tmp 3 MLCT states, presumably 3 A 1 and 3 B 2 . The high-energy emission is due predominantly to W→CO 3 MLCT state(s). Involvement of emissive 3 LF excited states, assumed previously, has been excluded. The emission behavior is qualitatively similar for both [W(CO) 4 (phen)] and [W(CO) 4 (tmp)], despite the different characters of their LUMOs; b 1 and a 2 , respectively.

A new kind of organometallic polymer of osmium(0) [Os0(bpy)(CO)2]n (bpy = 2,2′-bipyridine) has been prepared as a thin film on an electrode surface by electrochemical reduction of the mononuclear trans(Cl)-[OsII(bpy)(CO)2Cl2] precursor complex. This modified electrode proves to be a good electrocatalyst for the reduction of CO2 in aqueous media.

The spectroscopic and photochemical properties of a series of 1,5-cyclooctadiene platinum complexes of the type [(COD)Pt(R)2] (R=alkyl, alkynyl, or aryl) were examined. The observed photoreactivity is wavelength dependent and observed reaction rates correlate with the donor-strength of the R group. For strongly donating substituents like adamantylmethyl, benzyl or iso-propyl rates were increased by factors of about 100 for a given model reaction compared to the dimethyl derivative. The products were determined by NMR spectroscopy. Different reaction pathways were found depending on the substituents R. Theoretical calculations (DFT) on the electronic structure revealed the character of optical transitions and excited states.

The synthesis, structure and photochemistry of the novel rhodium(III) complexes cis,cis -[Rh(R) 2 (I)(CO)(dmb)] (R=Me ( 1 ), i Pr ( 2 )) are reported. Although many di- and trimethyl–rhodium(III) complexes are known, cis,cis -[Rh( i Pr) 2 (I)(CO)(dmb)] ( 2 ) is the first diisopropyl–rhodium(III) compound. Single-crystal X-ray diffraction studies revealed the structure of 1 . Resonance Raman spectra were obtained by excitation into the lowest-energy allowed electronic transition of the complexes. These spectra show that this transition has halide-to-ligand charge transfer (XLCT) character. Upon irradiation in solution, both 1 and 2 give rise to Rh–R bond homolysis as evidenced by IR, UV–vis and spin-trap EPR investigations. The photoreaction is proposed to occur after crossing from the XLCT state to the reactive sigma-bond-to-ligand charge transfer (SBLCT) state. For the i Pr-complex homolysis is observed at longer wavelength irradiation than for the methyl derivative, indicating that in the former case the reactive state is lower in energy.

The photophysical, photochemical and redox properties of the title complexes were investigated. Resonance Raman measurements revealed the lowest-energy electronic transition to possess σπ* character. At low temperatures, long-lived near-IR emission was observed. Irradiation in solution results in homolytic splitting of a Ru–Ru bond as the primary step, followed by secondary reactions of the radical fragments depending on the experimental conditions. (Spectro)electrochemical investigations of the title species proved that the axial [RuCp(CO)2] groups exert a stabilising influence on the corresponding radical cations, while destabilising the corresponding radical anions, compared to the redox behaviour of other ruthenium complexes of this type.

A novel family of paramagnetic tetranuclear ferrous cubanes is reported. Two complexes from this family are described and their magnetic properties are discussed in relation to their structures. © The Royal Society of Chemistry 2012

We report the synthesis, structures and magnetic properties of a series of chromium(III) metal-centered triangle (or >star>) clusters, [Cr 4{RC(CH2O)3}2(4,4′- R′2-bipy)3Cl6] [R = Et, R′ = H (2); R = HOCH2, R′ = H (3); R = Et, R′ = tBu (4)], prepared by two-step solvothermal reactions starting from [CrCl 3(thf)3]. The product of the first stage of this reaction is the salt [Cr(bipy)2Cl2]2[Cr 2Cl8(MeCN)2] (1). In the absence of the diimine, a different family of tetrametallics is isolated: the butterfly complexes [Cr4{EtC(CH2O)3}2{NH(C(R) NH)2}2Cl6] (R = Me (5), Et (6), Ph (7)] where the chelating N-acetimidoylacetamidine NH(C(R)NH)2 ligands are formed in situ via condensation of the nitrile solvents (RCN) under solvothermal conditions. Magnetic measurements show the chromium stars to have an isolated S = 3 ground state, arising from antiferromagnetic coupling between the central and peripheral metal ions, analogous to the well-known Fe(III) stars. Bulk antiferromagnetic ordering is observed at 0.6 K. The butterfly complexes have a singlet ground state, with a low-lying S = 1 first excited state, due to dominant wing-body antiferromagnetic coupling. © 2011 The Royal Society of Chemistry., The Spanish MICINN (contracts MAT2009-13977-C03 and CSD2007-00010) for funding.

The fixation of CO(2) at ambient temperature has been achieved by the reaction of Ni(cod)(2) and TMEDA in CO(2) saturated THF that yields a novel hexanuclear nickel(II) mu(3)-carbonato bridged complex [Ni(6)(mu(3)-CO(3))(4)(TMEDA)(6)(H(2)O)(12)](OH)(4) in 59% yield. The complex was characterised by MS analysis and the structure corroborated by single-crystal X-ray crystallography. The complex exhibits a rare carbonato binding mode for Ni(II) complexes and moderately strong antiferromagnetic interactions.

9 pages; International audience; Reaction of 2,4-(2,20-dipyridylamino)-6-(2-pyridylhydrazino)-1,3,5-triazine, abbreviated dppht (5), with copper(II) chloride in methanol yields a mixed-valent CuII 4CuI compound (6), also involving the presence of a radical anion. The single-crystal structure determination for [Cu5(5M)(5MR)Cl8] (6) reveals that the original dppht ligand (5) has been monochlorinated at one of its pyridine rings and oxidized at its hydrazyl moiety, generating the ligand 2,4-(2,20-dipyridylamino)-6-(2-(5- chloropyridyl)azo)-1,3,5-triazine (5M). Moreover, the molecular structure of 6 indicates that one of the two coordinated ligands 5M is in a radical-anion state, symbolized as 5MR, characterized by a typical N-N bond length of about 1.33A° for a one-electron reduced azo group. The nature of this unique [CuII 4CuI(radical)] assembly is corroborated by X-ray absorption spectroscopy, electron paramagnetic resonance, and magnetic susceptibility measurements. Density-functional theory calculations are consistent with the unprecedented structural features and support the spectroscopic data.

A new type of heteropolytungstate is reported that contains in a triangular arrangement one lanthanide f element and two d transition metals in form of heteroatoms. The first example in this series is the monoclinic Na3K5[((VO)(2)Dy(H2O)(4)K-2(H2O)(2)Na(H2O)(2))(alpha-B-AsW9O33)(2)] center dot a23H(2)O (1) which was prepared from an acidified aqueous solution of Na2WO4 center dot 2H(2)O, As2O3 and VOSO4 center dot 5H(2)O to which Dy3+ ions were added. The single crystal X-ray structure analysis shows that the anion 1a consists of two [alpha-B-(AsW9O33)-W-III](9-) trilacunary Keggin type units linked by two VO2+, one Dy3+ as well as two K+ stop and one Na+ ion, resulting in a sandwich-type structure with idealized C-2v symmetry. The complete magnetochemical analysis shows very interesting magnetic properties, which will be considered in the full series together with the properties of the homologous compounds in due course.

The cluster {(Mo)Mo-5}(12)Fe-30(III) 1 a present in compound 1 (cluster diameter 2.3 nm), which belongs to the family of nanoscale spherical porous {(Mo)Mo-5}(12){Linker}(30) capsules that allow a new type of nanochemistry inside their cavities as well as unprecedented aggregation processes under gaseous, solution, and solid-state conditions, is the starting material for the present investigation. In solution it reacts with LnCl(3)center dot-nH(2)O (Ln=Ce, Pr) thereby replacing six Fe-III ions with Ln(III) ions to form compounds 2 (Ce) and 3 (Pr). During metal-cation exchange, some of the pentagonal {(Mo)Mo5O21(H2O)(6)}(6-) units, which are connected to the Fe-III, centers in 1 a, decompose, thus leading to a temporary capsule opening and uptake of the formed smaller molybdate units into the capsule cavities. In 2 and 3, the pentagonal units are connected via 24 Fe-III and six Ln(III)-type linkers/spacers representing together the capsule skeletons, which are structurally well-defined in contrast to the capsule contents. The new capsules self-associate into single-layer blackberry-type structures, thus extending the variety of these types of assemblies; the assembly process, that is, the size of the final species, can be controlled by the pH, which allows the generation of differently sized nanoparticles. Magnetic properties of the two new nanomaterials 2 and 3 are also determined.

Recent work in designing and synthesising molecules displaying the phenomenon of “single molecule magnet” (SMM) behaviour has shown how a propeller motif with four paramagnetic metal centres can both stabilise non-zero ground spin states and display slow relaxation of the hysteresis: the signature of an SMM. Having thus identified the structural elements required it should be straightforward to produce new examples and learn how to enhance the SMM characteristics. Here we report on an attempt to do this with the surprising result that a molecule specifically designed to display SMM behaviour proves not to, posing the question as to why this should be.

The reaction of [H2AsIII-W18O60](7-) with VO2+ and SO42- ions in aqueous solution leads to a V-IV/V-V mixed-valence cluster anion containing the {AS(4)M(40)O(140)}-type cryptand which has a high formation tendency. An important result is that it exhibits a new type of reactive internal cavity shell. The correspondingly obtained compound Na(NH4)(20)[{((VO)-O-IV(H2O))((VVO)-V-IV)(2)- (SO4)(2)}{((AsW9O33)-W-III)(2)((AsW7.5V1.5O31)-W-III-O-V)(2)-(WO2)(4)}]- 40H(2)O (1), which can also be synthesized from a precursor with the preorganized cryptand, was characterized by elemental and thermogravimetric analyses (determination of crystal water content), redox titrations (determination of the number of V-IV centers), electronic absorption as well as vibrational spectra, single-crystal X-ray structure analysis (including bond valence sum calculations), and magnetic susceptibility measurements. The relatively small central cavity-formed by the linking of four {AsM9}-type lacunary units (M=W/V) by four WO6 octahedra-allows positioning of a variety of cationic as well as anionic "guests" under confined conditions according to a new approach: replacement of some of the W by V atoms leads to high reactivity of the internal cavity shell as a result of relatively weak VO bonds compared to the WO bonds. This allows an interesting "encapsulation chemistry" with new options. In the present case the cavity contains besides an arrangement of three V-IV centers, two sulfate groups that replace O atoms of the {AsM9} units as well as an interesting hydrogen bond situation.

The new redox systems [(acac)(2)Ru(u-Q(1))Ru(acac)(2)](n) (1(n)) and [(acac)(2)Ru(mu-Q(2))Ru(acac)(2)](n) (2(n)) with Q(1) = 1,10-phenanthroline-5,6-dione and Q(2) = 1,10-phenanthroline-5,6-diimine were studied for n = +, 0, -, and 2- using UV-Vis-NIR spectroelectrochemistry, and, in part, EPR and susceptometry. The ligands can bind the first metal (left) through the phenanthroline nitrogen atoms and the second metal (right) at the o-quinonoid chelate site. The neutral compounds are already different: Compound 1 is formulated as a Ru-II(mu-Q(1))(center dot-) Ru-III species with partially coupled semiquinone and ruthenium(III) centers. In contrast, a Ru-III(mu-Q(2))(2-) Ru-III structure is assigned to 2, which shows a weak antiferromagnetic spin-spin interaction (J = -1.14 cm(-1)) and displays an intense half-field signal in the EPR spectrum. The one-electron reduced forms are also differently formulated as Ru-II(mu-Q(1))(2-) Ru-III for 1(-) with a Ru-III-typical EPR response and as Ru-II(mu-Q(2))(center dot-) Ru-II for 2- with a radical-type EPR signal at g = 2.0020. In contrast, both 1(2-) and 2(2-) can only be described as Ru-II(mu-Q)(2-) Ru-II species. The monooxidized forms 1(+) and 2(+) show very similar spectroscopy, including a Ru-III-type EPR signal. Although no unambiguous assignment was possible here for the alternatives Ru-II(mu-Q)Ru-0(III), Ru-III(mu-Q)(2-) Ru-IV or Ru-III(mu-Q)(center dot-) Ru-III, the last description is favored. The reasons for identical or different oxidation state combinations are discussed.

A family of complexes of general formula [Co(CTH)(Phendiox)]Y·solv (CTH=tetraazamacrocycle; Phendiox=catecholato or semiquinonato form of 9,10-dioxophenanthrene; Y=PF 6 , I, BPh 4 ; solv=H 2 O, CH 2 Cl 2 , C 6 H 5 CH 3 ) were found to undergo valence tautomeric equilibria in the solid state. The interconversion involves an intramolecular electron transfer between a six-coordinated diamagnetic cobalt(III) metal ion and the coordinated polyoxolene ligand yielding a cobalt(II)–semiquinonato complex, the metal ion being in high spin configuration. All the synthesised complexes are diamagnetic at low temperature and high pressure and paramagnetic at high temperature and low pressure. These complexes were designed following electrochemical data. The critical interconversion temperature was found to depend on the nature of the counterion Y and on the nature of the solvent trapped in the lattice. No hysteresis was detected in the interconversion processes. However significant hysteresis effects were detected by substituting solvent from the lattice with its deuterated analogue and by using a partially deuterated ancillary macrocyclic ligand. The observed results are totally unpredictable and show how the emerging properties of a given set of molecules can be deeply influenced by very subtle and not controlled factors. Studies on closely related complexes were carried out for elucidating the electronic properties of these systems. In particular it was found that the [Co II (Me 4 cyclam)(SQ)]Y complexes (Me 4 cyclam=tetraazamacrocycle; SQ=semiquinonato radical ligand) are characterised by a weak anti-ferromagnetic coupling between the high-spin cobalt(II) ion and the paramagnetic ligand. In addition it was shown that the valence tautomeric interconversion could be photoinduced, the process involving two separate steps. DFT calculations show that in addition to the cobalt(III)–catecholato and hs -cobalt(II)–semiquinonato species which are involved in the thermal equilibrium, the third valence tautomer ls -cobalt(II)–semiquinonato species could be important from a photomagnetic point of view.

Resonance Raman spectra of heteroatom substituted ruthenium(II)-all enylidene complexes, obtained by irradiation into the second electronic absorption band, clearly prove the d(Ru) -> 1t*(CCC) MLCT character of the corresponding electronic transition . The complexes are not significantly luminescent at room temperature, but in solv ent glasses at 77 K, emission is observed. Only some of the complexes studied are luminescent upon irradiation into their lowest-energy absorption band. The striking finding of this study is that almost a ll complexes are luminescent on irrad iation into their second absorption band. The emission was shown to originate from a higher lying 3MLCT state, which shows that internal conversion to the lowest excited state is very inefficient in these complexes.

The conceptually simple mixed-valent diiron compound (NEt(4))(5)[(NC)(5)Fe(mu-tz)Fe(CN)(5)] with the 1,2,4,5-tetrazine (tz) bridging ligand was obtained as a thermally and air-stable material that displays large and highly variable electrochemical comproportionation constants between about 10(8) (in water) and 10(19.0) (in acetonitrile). Strong metal-metal interaction is also evident from spectroscopic results obtained for the solid and for the dissolved species. The rather intense intervalence charge-transfer band occurs around 2400 nm; infrared and Mossbauer spectra reveal the high spectroscopic symmetry of the system according to an (Fe(2.5))(2) formulation. DFT calculations on the [(NC)(5)Fe(mu-tz)Fe(CN)(5)](6-) ion confirm the presence of very low-lying pi(tz) and high-lying d(Fe) orbitals.

The ruthenium(II) organometallic and coordination complexes of type Ru(X)(Y)(CO)2(i-Pr-DAB) (i-Pr-DAB = 1,4-diisopropyl-1,4-diaza-1,3-butadiene; X, Y = Cl, Br, I, Me, Et, i-Pr, neo-Pe, Ph3Sn, Me3Sn, Ph3Pb, Ph3Ge, Mn(CO)5, RuCp(CO)2) have been analyzed by means of 99Ru NMR spectroscopy. The 99Ru NMR resonances for these compounds are generally sharp, allowing scalar couplings to group 14 nuclei to be observed. Correlation times τc have been determined from NOE factors and 13C T1 values for selected compounds and were found to parallel the molecular weight of the compounds studied. The M−Ru−M‘ and M−Ru−X complexes have 99Ru NMR resonances in distinct chemical shift regions. In the series M−Ru−M‘ a correlation between the inverse of the crystal field splitting energy ΔE and δ(99Ru) exists. These complexes have a HOMO which is delocalized over the M−Ru−M‘ σ system and a LUMO which has predominantly π*-DAB character; therefore, (ΔE)-1 is dominant in the paramagnetic shielding of the ruthenium nucleus. The diff...

The synthesis, structural and magnetic characterisation of trinuclear manganese cluster, [Mn(3)O(O(2)C-anth)(6)(HOCH(3))(3)] 1 (where O(2)C-anth = 9-anthracenecarboxylate), with crystallographic three-fold (C(3)) symmetry, are described. The cluster was prepared by a carboxylate exchange reaction between HO(2)C-anth and [Mn(12)O(12)(O(2)CMe)(16)(H(2)O)(4)] with concomitant fragmentation of the dodecanuclear Mn core of the starting material to form a trinuclear Mn(3)(μ(3)-O) cluster capped by six carboxylate ligands. Bond valence sum calculations and SQUID magnetometric measurements establish the oxidation states of the metal ions as Mn(II)·2 Mn(III) which are antiferromagnetically coupled.

A Magnetic Circular Dichroism (MCD) spectroscopic study of the antiferromagnetic ring [Cr8F8Piv16] (Piv = pivalate) is reported. From the splitting of the MCD bands, the single ion anisotropy parameters in the cluster spin ground state at different fields were determined to be dCr = −0.33 ± 0.02 cm−1, eCr = 0.11 ± 0.01 cm−1. Analysis of the MCD intensity as a function of field and temperature revealed the influence of spin mixing effects and yielded independent estimates of the single ion anisotropies (dCr = −0.19 cm−1, eCr = 4.3 × 10−4 cm−1), as well as yielding the isotropic exchange interaction strength (J = −6.00 cm−1). Thus it is shown that MCD is a powerful method to unravel the relation between single-ion and cluster anisotropy, furthering the design of molecular magnets with desired properties.

A series of homoleptic complexes with non-innocent ligands derived from N,N'-bis(pentafluorophenyl)-o-phenylenediamine (H(2)(F)pda) are reported. [Ni(II)((F)sbqdi)(2)] (1), [Pd(II)((F)sbqdi)(2)] (2), [Co(II)((F)sbqdi)(2)] (3), and [Cu(II)((F)sbqdi)(2)] (4) were synthesized, where ((F)sbqdi)(1-) represents a radical anion formed by one-electron oxidation of the doubly deprotonated H2(F)pda. The oxidation states of ligands and metals in complexes 1-4 were assigned by single crystal X-ray crystallography performed at low temperatures. Complex 4 is the first Cu(II) complex where both o-phenylenediamine derived ligands are monoanionic radicals. The bulky N-C6F5 substituents force the complexes 1, 3, and 4 to adopt a twisted geometry (intermediate between square-planar and tetrahedral). The electronic structures of the neutral compounds 1-4 and of some of their cationic and/or anionic neighboring redox states were probed using EPR and UV-VIS-NIR spectroelectrochemistry. The twisted geometry of the complexes results in considerable changes in their electronic structures compared to the well known square-planar complexes while the strongly electron withdrawing N-C6F5 groups have a great influence on redox properties.