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The reactions of the ditopic ligand 1,4-bis(2,2':6',2-terpyridin-4'-yl)benzene (1) as well as the monotopic ligands 4'-phenyl-2,2':6',2-terpyridine (2) and 2,2':6',2-terpyridine (3) with Fe2+, Co2+, and Ni2+ in solution are studied. While the reaction of 1 with Fe2+, Co2+, and Ni2+ results in metallo-supramolecular coordination polyelectrolytes (MEPEs), ligands 2 and 3 give mononuclear complexes. All compounds are analyzed by UV/vis and fluorescence spectroscopy. Fluorescence spectroscopy indicates that protonation as well as coordination to Zn2+ leads to an enhanced fluorescence of the terpyridine ligands. In contrast, Fe2+, Co2+, or Ni2+ quench the fluorescence of the ligands. The kinetics of the reactions are studied by stopped-flow fluorescence spectroscopy. Analysis of the measured data is presented and the full kinetic rate laws for the coordination of the terpyridine ligands 1, 2, and 3 to Fe2+, Co2+, and Ni2+ are presented. The coordination occurs within a few seconds, and the rate constant increases in the order Ni2+ < Co2+ < Fe2+. With the rate constants at hand, the polymer growth of Ni-MEPE is computed. [ABSTRACT FROM AUTHOR]

Seven new coordination polymers based on the redox-active tetra(4-pyridyl)-tetrathiafulvalene ligand (TTF(py)4) and different transition-metal ions, namely, {[Cu(hfac)2][TTF(py)4]·2(CH2Cl2)}n (1), {[Co(acac)2][TTF(py)4]0.5·(CHCl3)}n (2), {[Mn(hfac)2][TTF(py)4]0.5}n (3), {[Cu2(OAc)4][TTF(py)4]0.5·1.5(CHCl3)·0.5(H2O)·(CH3CN)}n (4), {[Mn(SCN)2][TTF(py)4]·6(CH2Cl2)}n (5), {[Mn(SeCN)Cl][TTF(py)4]}n (6), and {Cu2[TTF(py)4]2·(ClO4)2·2.5(CH2Cl2)·1.5(CH3CN)}n (7), were synthesized and characterized. The tetrapyridyl ligand coordinates to metal ions in a bidentate or tetradentate fashion, forming complexes 1-7 with different structures. Complex 1 exhibits a one-dimensional chain structure. Complexes 2, 3, and 4 possess similar (4,2)-connected binodal two-dimensional networks, while complexes 5 and 6 have similar (4,4)-connected binodal two-dimensional networks with two different rings. Complex 7 shows a 2-fold interpenetrated (4,4)-connected binodal PtS-type three-dimensional framework. Meanwhile, these complexes feature diverse nonclassical hydrogen bonding interactions. In addition, magnetic and solid-state electrochemical properties for typical complexes have been studied. [ABSTRACT FROM AUTHOR]

The reaction of 1,2,4-triazole and NaF with M(ox) (M = transition-metal dication; ox = oxalate dianion) under hydrothermal conditions has led to the isolation of a variety of hybrid organic–inorganic coordination polymers. Four structurally different 3D networks were obtained, depending on the transition metal, with stoichiometry [M2(H2O)(μ2-ox)][M2(μ3-trz)6] [M = Fe (1), Co (2), Ni (3)], [Zn2(H2O)(μ3-trz)2(μ2-ox)] (4), [Mn3(μ3-trz)2(μ6-ox)(μ3-F)2] (5), and [Fe3(μ3-trz)2(μ6-ox)(μ2-F)2] (6). In all cases, the magnetic behavior is dominated by antiferromagnetic exchange interactions between paramagnetic centers. Remarkably, 5 and 6 present a novel magnetic connectivity around the oxalate anion: a μ6-bridging mode. This magnetic geometry promotes multiple triangular arrangements among antiferromagnetically coupled spin carriers, resulting in a complex magnetic network because of the presence of competing interactions. These materials exhibit spontaneous magnetization below 9 and 66 K, respectively. [ABSTRACT FROM AUTHOR]

Superoxide dismutase (SOD) catalyzes the disproportionation of superoxide (O2•-) into H2O2 and O2(g) by toggling through different oxidation states of a first-row transition metal ion at its active site. Ni-containing SODs (NiSODs) are a distinct class of this family of metalloenzymes due to the unusual coordination sphere that is comprised of mixed N/S-ligands from peptide-N and cysteine-S donor atoms. A central goal of our research is to understand the factors that govern reactive oxygen species (ROS) stability of the Ni--S(Cys) bond in NiSOD utilizing a synthetic model approach. In light of the reactivity of metal-coordinated thiolates to ROS, several hypotheses have been proffered and include the coordination of His1-Nδ to the Ni(II) and Ni(III) forms of NiSOD, as well as hydrogen bonding or full protonation of a coordinated S(Cys). In this work, we present NiSOD analogues of the general formula [Ni(N2S)(SR')]-, providing a variable location (SR' = aryl thiolate) in the N2S2 basal plane coordination sphere where we have introduced o-amino and/or electron-withdrawing groups to intercept an oxidized Ni species. The synthesis, structure, and properties of the NiSOD model complexes (Et4N)[Ni(nmp)(SPh-o-NH2)] (2), (Et4N)[Ni(nmp)(SPh-o-NH2-p-CF3)] (3), (Et4N)[Ni(nmp)(SPh-p-NH2)] (4), and (Et4N)[Ni(nmp)(SPh-p-CF3)] (5) (nmp2- = dianion of N-(2-mercaptoethyl)picolinamide) are reported. NiSOD model complexes with amino groups positioned ortho to the aryl-S in SR' (2 and 3) afford oxidized species (2ox and 3ox) that are best described as a resonance hybrid between Ni(III)-SR and Ni(II)-•SR based on ultraviolet-visible (UV-vis), magnetic circular dichroism (MCD), and electron paramagnetic resonance (EPR) spectroscopies, as well as density functional theory (DFT) calculations. The results presented here, demonstrating the high percentage of S(3p) character in the highest occupied molecular orbital (HOMO) of the four-coordinate reduced form of NiSOD (NiSODred), suggest that the transition from NiSODred to the five-coordinate oxidized form of NiSOD (NiSODox) may go through a four-coordinate Ni-•S(Cys) (NiSODox-Hisoff) that is stabilized by coordination to Ni(II). [ABSTRACT FROM AUTHOR]

We systematically studied the solvothermal reactions of transition-metal ions and H4abtc ligand and successfully isolated five metal-organic frameworks with various characterized tools, which are formulated as {[Mn2(abtc)(DMA)2.75]·1.25(DMA)}n (1), {[NH2(CH3)2][Co3(COOH)2.5(abtc)(H2O)2]2·H2O}n (2), {[Zn3(abtc)1.5(DMF)3]·1.75(DMF)}n (3), {[Zn2(abtc)(H2O)0.75(DMA)0.5]·3(DMA)·(H2O)}n (4), and {[Cd2(abtc)(DMA)2]·2(DMA)}n (5), (H4abtc = 3,3',5,5'-azobenzenetetracarboxylic acid, DMF = N,N-dimethylformamide, and DMA = N,N-dimethylacetamide). 1-5 all consist of {Mn(CO2)4}-type clusters and H4abtc ligands; however, they exhibit four distinct architectures resulting from different coordinated modes of H4abtc ligand. A pair of Mn2+ions in 1 forms a {Mn2(CO2)4} cluster, which further results in the "PtS"-type three-dimensional (3D) framework. In 2, three independent CO2+ ions are bridged by COOH- groups to afford a {Co3} core, and {Co3} cores are connected by abtc2- to generate a "ZSW1"-type topology. Two types of {Zn2(CO2)4} secondary building units in 3 linked by abtc2- give the 3D "NbO"-type cage. When DMF is replaced by DMA and CH3OH, the scarce "nou"-type topology of 4 is obtained. And 5 is isomorphous to 1. Photoluminescence properties of 1-5 were characterized. Magnetic measurements demonstrate that dominant antiferromagnetic interactions exist in 1 and 2. In addition, 3 exhibits significant adsorption capability of CO2 and highly selective sorption of CO2 over n2. [ABSTRACT FROM AUTHOR]

2-Amino-2-hydroxymethyl-propane-1,3-diol, or tris(hydroxymethyl)aminomethane (Tris), is probably the most common biochemical buffer used alone or in combination with other buffers because it is stable, unreactive, and compatible with most proteins and other biomolecules. Being nontoxic, it has even found applications in medicine. Tris is known, however, to coordinate transition metal ions, Cu(II) among them. Although often ignored, this feature affects interactions of Cu(II) ions with biomolecules, as Tris is usually used in high molar excess. Therefore, it is important to have precise knowledge on the stoichiometry, stability, and reactivity of cupric Tris complexes. The literature data are incoherent in this respect. We reinvestigated the complex formation in the Tris-Cu(II) system by potentiometry, UV-vis, ESI-MS, and EPR at a broad range of concentrations and ratios. We found, contrary to several previous papers, that the maximum stoichiometry of Tris to Cu(II) is 2 and at neutral pH, dimeric complexes are formed. The apparent affinity of Tris buffer for Cu(II), determined by the competitivity index (CI) approach [Krężel, A.; Wójcik, J.; Maciejczyk, M.; Bal, W. Chem. Commun. 2003, 6, 704-705] at pH 7.4 varies between 2 × 106 and 4 × 104 M-1, depending on the Tris and Cu(II) concentrations and molar ratio. [ABSTRACT FROM AUTHOR]

We present the first comparative investigation of the Nuclear Magnetic Resonance (NMR) relaxivity of a series of nanosized cyano-bridged coordination networks stabilized in aqueous solution. These Ln3+/[Fe(CN)6]3- (Ln = Gd, Tb, Y) and M2+/[Fe(CN)6]3- (M = Ni, Cu, Fe) nanoparticles with sizes ranging from 1.4 to 5.5 nm are stabilized by polyethylene glycols (MW = 400 or 1000), polyethylene glycol functionalized with amine groups (MW = 1500), or by N-acetyl-d-glucosamine. The evaluation of NMR relaxivity allowed estimation of the Magnetic Resonance Imaging (MRI) contrast efficiency of our systems. The results demonstrate that Gd3+/[Fe(CN)6]3- nanoparticles have r1p and r2p relaxivities about four times higher than the values observed in the same conditions for the commercial Contrast Agents (CAs) ProHance or Omniscan, regardless of the stabilizing agent used, while nanoparticles of Prussian blue and its analogues M2+/[Fe(CN)6]3- (M = Ni, Cu, Fe) present relatively modest values. The influence of the chemical composition of the nanoparticles, their crystal structure, spin values of lanthanide and transition metal ions, and stabilizing agent on the relaxivity values are investigated and discussed [ABSTRACT FROM AUTHOR]

The reaction of first row transition MII ions with KSCN in various solvents form tetrahedral (NMe4)2[MII(NCS)4] (M = Fe, Co), octahedral trans-MII(NCS)2(Sol)4 (M = Fe, V, Ni; Sol = MeCN, THF), and K4[MII(NCS)6] (M = V, Ni). The reaction of M(NCS)2(OCMe2)2 (M = Cr, Mn) in MeCN and [Co(NCMe)6](BF4)2 and KSCN in acetone and after diffusion of diethyl ether form M(NCS)2(Sol)2 that structurally differ as they form one-dimensional (1-D) (M = Co; Sol = THF), two-dimensional (2-D) (M = Mn; Sol = MeCN), and three-dimensional (3-D) (M = Cr; Sol = MeCN) extended structures. 1-D Co(NCS)2(THF)2 has trans-THFs, while the acetonitriles have a cis geometry for 2- and 3-D M(NCS)2(NCMe)2 (M = Cr, Mn). 2-D Mn(NCS)2(NCMe)2 is best described as MnII(μN,N-NCS)(μN,S-NCS)(NCMe)2 [= Mn2(μN,N-NCS)2(μN,S-NCS)2(NCMe)4] with the latter μN,S-NCS providing the 2-D connectivity. In addition, the reaction of Fe(NCS)2(OCMe2)2 and 7,7,8,8-tetracyanoquino-p-dimethane (TCNQ) forms 2-D structured FeII(NCS)2TCNQ. The magnetic behavior of 1-D Co(NCS)2(THF)2 can be modeled by a 1-D Fisher expression (H = -2JSi·Sj) with g = 2.4 and J/kB = 0.68 K (0.47 cm-1) and exhibit weak ferromagnetic coupling. Cr(NCS)2(NCMe)2 and FeII(NCS)2TCNQ magnetically order as antiferromagnets with Tc's of 37 and 29 K, respectively, while Mn(NCS)2(NCMe)2 exhibits strong antiferromagnetic coupling. M(NCS)2(THF)4 and K4[M(NCS)6] (M = V, Ni) are paramagnets with weak coupling between the octahedral metal centers. [ABSTRACT FROM AUTHOR]

We describe the synthesis, crystal structures, and optical absorption spectra of transition metal-substituted spiroffite derivatives, Zn2-xMxTe3O8 (MII = Co, Ni, Cu; 0 < x ≤ 1.0). The oxides are readily synthesized by solid state reaction of stoichiometric mixtures of the constituent binaries at 620 °C. Reitveld refinement of the crystal structures from powder X-ray diffraction (XRD) data shows that the Zn/MO6 octahedra are strongly distorted, as in the parent Zn2Te3O8 structure, consisting of five relatively short Zn/MII-O bonds (1.898-2.236 Å) and one longer Zn/MnII-O bond (2.356- 2.519 Å). We have interpreted the unique colors and the optical absorption/diffuse reflectance spectra of Zn2-xMxTe3O8 in the visible, in terms of the observed/irregular coordination geometry of the Zn/MII-O chromophores. We could not however prepare the fully substituted M2Te3O8(MII = Co, Ni, Cu) by the direct solid state reaction method. Density Functional Theory (DFT) modeling of the electronic structure of both the parent and the transition metal substituted derivatives provides new insights into the bonding and the role of transition metals toward the origin of color in these materials. We believe that transition metal substituted spiroffites Zn2-xMxTe3O8 reported here suggest new directions for the development of colored inorganic materials/pigments featuring irregular/distorted oxygen coordination polyhedra around transition metal ions. [ABSTRACT FROM AUTHOR]

8-Hydroxyquinolines (8HQ) have found widespread application in chemistry and biology due to their ability to complex a range of transition metal ions. The family of 2- substituted 8HQs has been proposed for use in the treatment of Alzheimer's disease (AD). Most notably, the therapeutic PBT2 (Prana Biotechnology Ltd.) has been shown to act as an efficient metal chaperone, disaggregate metal-enriched amyloid plaques comprised of the Aβ peptide, inhibit Cu&/A#946; redox chemistry, and reverse the AD phenotype in transgenic animal models. Yet surprisingly little is known about the molecular interactions at play. In this study, we show that the homologous ligand 2-[(dimethylamino)methyl]-8-hydroxyquinoline (HL) forms a CuL complex with a conditional (apparent) dissociation constant of 0.33 nM at pH 6.9 and is capable of forming ternary Cu2+ complexes with neurotransmitters including histamine (HA), glutamic acid (Glu), and glycine (Gly), with glutathione disulfide (GSSG), and with histidine (His) side chains of proteins and peptides including the Aβ peptide. Our findings suggest a molecular basis for the strong metal chaperone activity of PBT2, its ability to attenuate Cu2+/Aβ interactions, and its potential to promote neuroprotective and neuroregenerative effects. [ABSTRACT FROM AUTHOR]

Metal chelators are potential therapeutic agents for treating diseases such as Wilson's and Alzheimer's where the pathology involves an excess of metal-ions (Cu(II) and Zn(II)/Cu(II)/Fe(II/III), respectively). In addition to the high affinity of the metal-ion to the chelators, metal selectivity of the chelators is essential to achieve the therapeutic goal, that is, the successful removal of excess of harmful metal-ions in a physiological extracellular medium rich in alkali and alkali earth metal-ions. For this purpose, we synthesized a novel chelator, methylenediphosphonotetrathioate (MDPT) which is the tetrathio analogue of methylenediphosphonic acid (MDP). MDPT was synthesized from bis-methylene(phosphonicdichloride) in a 3-step synthesis and a 31% overall yield. MDPT formed a stable complex with Zn(II) (log K = 10.84), which is 10(7) times more stable than the corresponding Ca(II) complex. Moreover, the MDPT-Zn(II) complex was 50-fold more stable than the MDP-Zn(II) complex. In addition, MDPT was found to inhibit the Cu(I)-catalyzed Fenton reaction (IC50 26 µM) 2.5 times more potently than a Fe(II)-catalyzed Fenton reaction, and 2.5 times more potently than EDTA (IC50 64 µM) in the Cu(I)/H2O2 system, as monitored by electron spin resonance (ESR). Furthermore, MDPT was found to be relatively stable in both acidic (pD 1.9, t1/2 = 71.5 h) and basic media (pD 12.4, t1/2 = 81 h) as monitored by (31)P/(1)H NMR. However, MDPT was not stable in air because of intramolecular oxidation and disulfide formation (33% oxidation after 27 h). In conclusion, MDPT was found to be a water-soluble chelator showing a clear preference to soft/borderline metal-ions and a remarkable selectivity to those metal-ions vs Ca(II) ions. The relative sensitivity of MDPT to oxidation may limit its use; however, the application of MDPT in acidic or basic media will increase its lifetime. [ABSTRACT FROM AUTHOR]

A series of six mixed-valence Mn(II)/Mn(III) dinuclear complexes were synthesized and characterized by X-ray diffraction. The reactivity of the complexes was surveyed, and structures of three additional trinuclear mixed-valence Mn(III)/Mn(II)/Mn(III) species were resolved. The magnetic properties of the complexes were studied in detail both experimentally and theoretically. All dinuclear complexes show ferromagnetic intramolecular interactions, which were justified on the basis of the electronic structures of the Mn(II) and Mn(III) ions. The large Mn(II)-O-Mn(III) bond angle and small distortion of the Mn(II) cation from the ideal square pyramidal geometry were shown to enhance the ferromagnetic interactions since these geometrical conditions seem to favor the orthogonal arrangement of the magnetic orbitals. [ABSTRACT FROM AUTHOR]

A series of new mixed-metal oxalates containing U4+ and divalent transition metal cations, Na²U²M(C²O4)6(H²O)4 (M = Mn2+, Fe2+, Co2+, and Zn2+), were synthesized via a hydrothermal route and structurally characterized by single crystal X-ray diffraction. All of the materials are triclinic, with space group P¯1. The three-dimensional structure of these isostructural uranates consists of oxalate bridged UO(10) and MO6 polyhedra. The U4+ cation is surrounded by five oxalate ligands, while the M2+ cations are bonded to two oxalate ligands and four water molecules. The magnetic susceptibility data of these mixed metal oxalates were measured as a function of temperature and result in a value of the effective magnetic moment of 3.50 ÎB for U4+ cation in the Zn member, while the total effective moment of the Mn2+, Fe2+, and Co2+ members are 6.01, 5.46, and 5.06 ÎB, respectively. For all materials, negative Weiss constants were observed revealing that the materials exhibited local antiferromagnetic interactions. The U4+ cation exhibits a singlet ground state at low temperature. The materials were further characterized by infrared, UV-vis reflectance spectroscopy, and thermal analysis. [ABSTRACT FROM AUTHOR]

A new dibenzotetraaza[14]annulene bearing two 3,3-dimethylindolenine fragments at the meso positions (LH2), has been synthesized through a nontemplate method. X-ray crystallography shows that the whole molecule is planar. The basicity of the indolenine ring permits the macrocycle to be protonated external to the core and form LH42+-2Cl-. Yet another structural modification having strong C--H···π interactions was found in the chloroform solvate of LH2. The latter two modifications are accompanied by a degree of nonplanar distortion. The anti aromatic core of die macrocycle can accommodate a number of metal ions, MnIII, FeIII, CoII, NiII and CuII, to form complexes of [Mn(L)Br], [Mn(L)Cl], [Fe(LH2)Cl2]+·Cl-, [Co(L)], [Ni(L)], and [Cu(L)]. In addition, the reaction of LH2 with the larger PdII ion leads to the formation of [Pd2(LH2)2(OAc)4] wherein the macrocycle acts as a semiflexible ditopic ligand to coordinate pairs of metal ions via its indolenine N atoms into dinuclear metallocycles. The compounds LH2, [Co(L)], and [Ni(L)] are isostructural and feature close π-stacking as well as linear chain arrangements in the case of the metal complexes. Variable temperature magnetic susceptibility measurements showed thermally induced paramagnetism in [Ni(L)]. [ABSTRACT FROM AUTHOR]

The reaction mechanism of the dinuclear cobalt enzyme arginase is investigated using density functional theory. As an arginase-containing binuclear Mn2 2+ cluster, it catalyzes the hydrolysis of L-arginine in L-ornithine and urea. The bridging hydroxide is capable of performing nucleophilic attack on the iminium carbon ion from its bridging position, resulting in the formation of a tetrahedral intermediate, as was already obtained in a previous theoretical study on the manganese enzyme. Our theoretical investigation allows us to obtain an accurate potential energy profile and corifirms that the coordination mode of the substrate to the dimetallic center is quite similar to that present in die manganese enzyme. In agreement with the experimental observations, our results show that both Mn- and Co-containing enzymes catalyze die same reaction with quite comparable energy barriers. [ABSTRACT FROM AUTHOR]

Fluorescent detecting and tracking of zinc ions in living cells has become more and more important because the physiological and pathological functions of zinc are highly associated with the timing and discrete distribution of subcellular zinc ion. For the detection of subcellular zinc concentrations with high spatial and temporal reliability, we report the design, synthesis, properties, and bioimaging evaluation of a fluorescent probe, DQZn4, composed of a quinoline scaffold as the ratiometric signaling unit for Zn2+ and a dimethylethylamino group as the targeting anchor for lysosomes. In acidic aqueous solution (pH = 5.2), DQZn4 features fluorescence emission maximum at 542 nm due to the resonance charge transfer in 4-alkoxy substituted quinoline. Upon binding Zn2+, the probe displays significant fluorescent tum-on and ratiometric detection of Zn2+ with blue shift of 47 nm and remarkable fluorescence ratio changes (R = F495/F542 nm, R/R0 = 5.1). Confocal imaging experiments establish that DQZn4 is able to localize to lysosomes and respond to lysosomal zinc changes in living cells by using fluorescence ratiometry. [ABSTRACT FROM AUTHOR]

The spin reorientation (SR) phenomenon of the square-lattice antiferromagnets RMnAsO (R = Ce, Nd) was investigated by analyzing the spin-exchange interactions between the rare-earth and the transition-metal ions (R3+ and Mn2+, respectively) on the basis of density functional calculations. It is found tliat the symmetry and strength of the Dzyaloshinskii--Moriya (DM) interaction are determined primarily by the partially filled 4f states of the R3+ ions and that the DM and biquadratic (BQ) exchanges between the R3+ and the Mn2+ ions are unusually strong and control tlie observed spin reorientation phenomenon. Below their SR temperature, the Mn2+ and Ce3+ moments are orthogonal in CeMnAsO but are a)Uinear in NdMnAsO, because the DM interaction dominates over the BQ_interaction for CeNfaAsO, while the opposite is the case for NdMnAsO. Experiments designed to test the implications of our findings are proposed. [ABSTRACT FROM AUTHOR]

In this work, the high-pressure behavior of Pmn21-Li2MnSiO4 and Pbn21-Li2CoSiO4 is followed by in situ X-ray diffraction at room temperature. Bulk moduli are 81 and 95 GPa for Pmn21-Li2MnSiO4 and Pbn21-Li2CoSiO4, respectively. Regardless of the moderate values of the bulk moduli, there is no evidence of any phase transformation up to a pressure of 15 GPa. Pmn21-Li2MnSiO4 shows an unusual expansion of the a lattice parameter upon compression. A density functional theory investigation yields lattice parameter variations and bulk moduli in good agreement with experiments. The calculated data indicate that expansion of the a lattice parameter is inherent to the crystal structure and independent of the nature of the transition-metal atom (M). The absence of pressure-driven phase transformation is likely associated with the incapability of the Li2MSiO4 composition to adopt denser structures while avoiding large electrostatic repulsions. [ABSTRACT FROM AUTHOR]

[DyIII(HBpz3)2]2+ moieties (HBpz3- = hydrotris(pyrazolyl)borate) and a 3d transition-metal ion (FeIII or CoIII) have been rationally assembled using an dithiooxalato dianion ligand into 3d-4f [MDy3(HBpz3)6(dto)3]·4CH3CN·2CH2Cl2 (M = Fe (1), Co (2) complexes. Single-crystal X-ray studies reveal that three eight-coordinated DyIII centers in a square antiprismatic coordination environment are connecting to a central octahedral trivalent Fe or Co ion forming a propeller-type complex. The dynamics of the magnetization in the two isostructural compounds, modulated by the nature of the central MIII metal ion, are remarkably different despite their analogous direct current (dc) magnetic properties. The slow relaxation of the magnetization observed for 2 mainly originates from isolated Dy ions, since a diamagnetic CoIII metal ion links the magnetic DyIII ions. In the case of 1, the magnetic interaction between S = 1/2 FeIII ion and the three DyIII magnetic centers, although weak, generates a complex energy spectrum of magnetic states with low-lying excited states that induce a smaller energy gap than for 2 and thus a faster relaxation of the magnetization. [ABSTRACT FROM AUTHOR]

Reactions of a tripodal ligand, N,N′,N″-tris(3-pyridinyl)phosphoric triamide (TPPA), and a series of transition-metal ions result in the assembly of five discrete M6L8 coordination cages [M6(TPPA)8(H2O)12](ClO4)12·57H2O [M = Ni2+ (1), Co2+ (2), Zn2+ (3), Cd2+ (4)] and [Pd6(TPPA)8]Cl12·22H2O (5). X-ray structural analyses reveal that the cages have large internal cavities and flexible windows. The flexible ligand TPPA adopts the syn conformation in cages 1-4, but it transforms to the anti conformation in cage 5. Because of the conformational transformation, the sizes of the windows and the volume of the internal cavity of cage 5 are increased. 1H NMR and electrospray mass spectrometric studies show that cage 5 maintains its structural integrity in solution. Additionally, compounds 3 and 4 exhibit strong blue fluorescent emissions, which are 1 order of magnitude higher than that of the free ligand. [ABSTRACT FROM AUTHOR]

A complete potentiometric and NMR relaxometric solution study on the heptadentate 2,2',2?,2'?-[(6-piperidinyl-1,3,5-triazine-2,4-diyl)dihydrazin-2-yl-1-ylidene]tetraacetic acid (PTDITA) ligand has been carried out. This ligand is based on the 1,3,5-triazine ring with two hydrazine-N,N-diacetate groups in positions 2 and 4 and a piperidine moiety in position 6. The introduction of the triazine ring into the ligand backbone is expected to modify its flexibility and then to affect the stability of the corresponding complexes with transition-metal and lanthanide ions. Thermodynamic stabilities have been determined by pH potentiometry, UV spectrophotometry, and 1H NMR spectroscopy for formation of the complexes with Mg2+, Ca2+, Cu2+, Zn2+, La3+, Gd3+, and Lu3+ ions. PTDITA shows a good binding affinity for Gd3+ (logK = 18.49, pGd = 18.6) and an optimal selectivity for Gd3+ over the endogenous Ca2+, Zn2+, and Cu2+ (Ksel = 6.78 × 107), which is 3 orders of magnitude higher that that reported for Gd(DTPA) (Ksel = 2.85 × 104). This is mainly due to the lower stability of the CuII- and ZnII(PTDITA) complexes compared to the corresponding DTPA complexes, which suggests an important role of the triazine ring on the selectivity for the Gd3+ ion. The relaxometric properties of Gd(PTDITA) have been investigated in aqueous solution by measuring the 1H relaxivity as a function of the pH, temperature, and magnetic field strength (nuclear magnetic relaxation dispersion profile). Variable-temperature 17O NMR data have provided direct information on the kinetic parameters for exchange of the coordinated water molecules. A simultaneous fit of the data suggests that the high relaxivity value (r1 = 10.2 mM-1 s-1) is a result of the presence of two inner-sphere water molecules along with the occurrence of relatively slow rotation and electronic relaxation. The water residence lifetime, 298τM = 299 ns, is quite comparable to that of clinically approved magnetic resonance imaging contrast agents. The displacement of the inner-sphere water molecules by bidentate endogeneous anions (citrate, phosphate, and carbonate) has also been evaluated by 1H relaxometry. In general, the binding interaction is markedly weak, and only in the case of citrate, a ca. 35% decrease in relaxivity was observed in the presence of 60 equiv of the anion. Phosphate and carbonate also interact with the paramagnetic ion, likely as monodentate ligands, but formation of the ternary complex is accompanied by a modest increase of r1 due to the contribution of second-sphere water molecules. [ABSTRACT FROM AUTHOR]

New pentaquinone derivatives 5 and 8 having rhodamine moieties have been designed and synthesized that undergo through-bond energy transfer (TBET) in the presence of Hg2+ ions among the various cations (Cu2+, Pb2+, Fe2+, Fe3+, Zn2+, Ni2+, Cd2+, Co2+, Ag+, Ba2+, Mg2+, K+, Na+, and Li+) tested in mixed aqueous media. [ABSTRACT FROM AUTHOR]

Dark red crystals of Y8S14.8, Tb8S14.8, Dy8S14.9, and Ho8S14.9 have been obtained following different reaction routes. The isostructural title compounds adopt the Gd8Se15 type, a 24-fold superstructure of the ZrSSi-type and can be described in space group A112 (non standard setting of C121, no. 5) with lattice parameter of a = 11.505(1) Å, b = 15.385(1) Å, c = 15.726(1) Å, and γ = 90.21(2)° for Y8S15-x; a = 11.660(1) Å, b = 15.468(2) Å, c = 15.844(2) Å, and γ = 90.19(2)° for Tb8S15-x; a = 11.584(1) Å, b = 15.340(2) Å, c = 15.789(2) Å, and γ = 90.34(2)° for Dy8S15-x; and a = 11.538(1) Å, b = 15.288(2) Å, c = 15.740(2) Å, and γ = 90.23(1)° for Ho8S15-x, respectively. The structure consists of an alternating stacking of puckered [RES] (RE, rare-earth metals) double slabs and planar sulfur layers along [001]. The planar sulfur layers have a complex arrangement of S22- dinuclear dianions, isolated S2- ions, and vacancies. All compounds contain trivalent rare-earth metal ions, for Tb8S15-x and Dy8S15-x antiferromagnetic order was found at TN = 5.4(2) K and 3.8(1) K, respectively. Short wavelength cutoff optical band gaps of 1.6 to 1.7 eV were determined. [ABSTRACT FROM AUTHOR]

The ligand N,N′-bis(2-pyridylmethyl)-bis(ethylacetate)-1,2-ethanediamine (debpn) coordinates divalent transition metal ions in either a pentadentate or hexadentate fashion. The coordination number correlates with the ionic radius of the metal ion, with larger cations being heptacoordinate as assessed by solid-state analysis. With Mn(II), the debpn ligand is hexadentate and remains bound to the oxophilic metal ion, even when dissolved in water. The ligand's incomplete coordination of the manganous ion allows water molecules to coordinate to the metal center. These two properties, coupled with the high paramagnetism associated with the S = 5/2 metal center, enable [Mn(debpn)(H2O)](ClO4)2 to serve as a stable and effective magnetic resonance imaging contrast agent despite the ligand's lack of both a macrocyclic component and an anionic charge. [ABSTRACT FROM AUTHOR]

A new tumor-seeking tridentate topology consisting of a phosphino dithioether ((HOCH2)2PCH2CH2S(CH2)nCH2SR; PS2) ligand framework for the production of kinetically inert and in vivo stable facial [99mTc(CO)3(PS2)]+ or [Re(CO)3(PS2)]+ is described. The X-ray crystal structure of fac-Re(CO)3(PS2)PF6 is reported. The bioconjugation strategies for incorporating bombesin (BBN) peptides on to the PS2 tripodal framework and, thereby, de novo designing of GRP receptor-seeking Tc(PS2-BBN)(CO)3 are developed. [ABSTRACT FROM AUTHOR]

The nature of the products of the reactions of [Ru3(CO)12] with diaminogermylenes depends upon the volume and the cyclic or acyclic structure of the latter. Thus, the triruthenium cluster [Ru3{μ-Ge(NCH2CMe3)2C6H4}3(CO)9], which has a planar Ru3Ge3 core and an overall C3h symmetry, has been prepared in quantitative yield by treating [Ru3(CO)12] with an excess of the cyclic 1,3-bis(neo-pentyl)-2-germabenzimidazol-2-ylidene in toluene at 100 °C, but under analogous reaction conditions, the acyclic and bulkier Ge(HMDS)2 (HMDS = N(SiMe3)2) quantitatively leads to the mononuclear ruthenium(0) derivative [Ru{Ge(HMDS)2}2(CO)3]. Mixtures of products have been obtained from the reactions of [Ru3(CO)12] with the cyclic and very bulky 1,3-bis(tert-butyl)-2-germaimidazol-2-ylidene under various reaction conditions. The Ru3Ge3 and RuGe2 products reported in this paper are the first ruthenium complexes containing diaminogermylene ligands. [ABSTRACT FROM AUTHOR]

The substitution of nucleobases in nucleic acid duplexes with ligands that have high affinity for transition metal ions creates metal-binding sites at specific locations within the duplexes. Several studies on the incorporation of metal ions into DNA and peptide nucleic acid (PNA) duplexes have suggested that the stability constant of the metal complex formed within the duplexes is a primary determinant of the thermal stability of the duplexes. To understand this relationship, we have synthesized two PNA monomers that carry the same ligand, namely 8-hydroxyquinoline, but have this ligand attached differently to the PNA backbone. The PNA monomers have been incorporated into PNA duplexes. UV and CD spectroscopy and calorimetric studies of the 8-hydroxyquinoline-PNA duplexes showed that the effect of the stability of the metal complex on the PNA duplexes was significantly modulated by the steric relationship between the complex and the duplex. This information is useful for the construction of hybrid inorganic-nucleic acid nanostructures. [ABSTRACT FROM AUTHOR]

Two copper(II) complexes, 1 and 2 with L1 and L2 [L1 = 2- aminomethyl pyridine; L2 = bis-(2-aminoethyl)amine], respectively, in degassed acetonitrile solvent, on exposure to NO gas, were found to form a thermally unstable [CuII-NO] intermediate which then resulted in the reduction of the copper(II) centers. The formation of the [CuII-NO] intermediate was evidenced by UV-visible, FT-IR, and EPR spectroscopic studies. The reduction of the copper(II) centers by nitric oxide afforded ligand transformation through diazotization at the primary amine coordination site, in both cases. The modified ligands, in each case, were isolated and characterized. [ABSTRACT FROM AUTHOR]

A series of coordination polymers with anionic, cationic, and neutral metal-carboxylate frameworks have been synthesized by using a flexible tetrapodal ligand tetrakis[4-(carboxyphenyl)oxamethyl] methane acid (H4X). The reactions between divalent transition-metal ions and H4X ligands gave [M3X2]·[NH2(CH3)2]2·8DMA (M = Co (1), Mn (2), Cd(3)) which have anionic metal-carboxylate frameworks with NH2(CH3)2+ cations filled in channels. The reactions of trivalent metal ions Y(III), Dy(III), and In(III) with H4X ligands afforded cationic metal-carboxylate frameworks [M3X2·(NO3)·(DMA)2·(H2O)]·5DMA·2H2O (M = Y(4), Dy(5)) and [In2X·(OH)2]·3DMA·6H2O (6) with the NO3− and OH− serving as counterions, respectively. Moreover, a neutral metal-carboxylate framework [Pb2X·(DMA)2]·2DMA (7) can also be isolated from reaction of Pb(II) and H4X ligands. The charged metal-carboxylate frameworks 1−5 have selectivity for specific counterions in the reaction system, and compounds 1 and 2 display ion-exchange behavior. Moreover, magnetic property measurements on compounds 1, 2, and 5 indicate that there exists weak antiferromagnetic interactions between magnetic centers in the three compounds. [ABSTRACT FROM AUTHOR]

A new three-dimensional magnesium formate polymorph, namely, γ-[Mg3(O2CH)6] has been synthesized via in situ formate anion generation method. γ-Mg-formate crystallizes in space group Pbcn, and structural determination by X-ray single crystal diffraction reveals a three-dimensional network of Mg2+ linked by formate anions. All formate anions possess similar binding mode to the metal center with one oxygen of a particular formate anion binds to one metal center (μ1 oxygen) and other oxygen binds to two metal centers (μ2 oxygen). N2 adsorption studies indicate that the framework displays permanent porosity. The specific surface area of γ-Mg-formate (BET, 120 m2 gm-1) is lower than the α- polymorph (BET, 150 m2 gm-1). However, the initial hydrogen uptake of γ-Mg-formate reached almost 1.0 wt % when the adsorbate pressure approached 760 Torr at 77 K. This is higher than the hydrogen uptake of α-Mg-formate (0.6 wt %). γ-Mg-formate, shows a moderate affinity and capacity for CO2 (3.4 Å kinetic diameter) at 298 K. The CO2 uptake at 760 Torr is 2.01 mmol gm-1(47.0 cc gm-1). Although this CO2 uptake is somewhat modest, it compares well with the CO2 uptake of several Mg-MOFs and ZIFs reported in the literature. [ABSTRACT FROM AUTHOR]

Density functional theory calculations have been performed for the terminal borylene, alylene, and gallylene complexes [(η5-C5H5)(CO)3M(ENR2)] (M = V, Nb; E = B, Al, Ga; R = CH3, SiH3, CMe3, SiMe3) using the exchange correlation functional BP86. The calculated geometry parameters of vanadium borylene complex [(η5-C5H5)(CO)3V{BN(SiMe3)2}] are in excellent agreement with their available experimental values. The M-B bonds in the borylene complexes have partial M-B double-bond character, and the B-N bonds are nearly B-N double bonds. On the other hand, the M-E bonds in the studied metal alylene and gallylene complexes represent M-E single bonds with a very small M-E π-orbital contribution, and the Al-N and Ga-N bonds in the complexes have partial double-bond character. The orbital interactions between metal and ENR2 in [(η5-C5H5)(CO)3M(ENR2)] arise mainly from M ← ENR2 σ donation. The π-bonding contribution is, in all complexes, much smaller. The contributions of the electrostatic interactions ΔEelstat are significantly larger in all borylene, alylene, and gallylene complexes than the covalent bonding ΔEorb; that is, the M-ENR2 bonding in the complexes has a greater degree of ionic character. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) doped with transition-metal ions (M) has potentially broad applications in photocatalysis, photovoltaics, and photosensors. One approach to these materials is through controlled hydrolysis of well-defined transition-metal titanium oxo cage compounds. However, to date very few such cages have been unequivocally characterized, a situation which we have sought to address here with the development of a simple synthetic approach which allows the incorporation of a range of metal ions into titanium oxo cage arrangements. The solvothermal reactions of Ti(OEt)4 with transition-metal dichlorides (MIICl2, M = Co, Zn, Fe, Cu) give the heterometallic transition-metal titanium oxo cages [Ti4O(OEt)15(MCl)] [M = Co (2), Zn (3), Fe (4), Cu (5)], having similar MTi4(μ4-O) structural arrangements involving ion pairing of [Ti4O(OEt)15]- anion units with MCl+ fragments. In the case of the reaction of MnCl2, however, two MnII ions are incorporated into this framework, giving the hexanuclear Mn2Ti4(μ4-O) cage [Ti4O(OEt)15(Mn2Cl3)] (6) in which the MCl+ fragments in 2-5 are replaced by a [ClMn(μ-Cl)MnCl]+ unit. Emphasizing that the nature of the heterometallic cage is dependent on the metal ion (M) present, the reaction of Ti(OEt)4 with NiCl2 gives [Ti2(OEt)9(NiCl)]2 (7), which has a dimeric Ni(μ-Cl)2Ni bridged arrangement arising from the association of [Ti2(OEt)9]- ions with NiCl+ units. The syntheses, solid-state structures, spectroscopic and magnetic properties of 2-7 are presented, a first step toward their applications as precursor materials. [ABSTRACT FROM AUTHOR]

Systematic explorations of the new phases in the PbII/BIII-TM(do/d1)-SeIV-O systems by hydrothermal syntheses led to tive new quatemary phases whose structures are composed ot three different asymmetdc building units, namely, Pb2VV2Se2O11 (1), Pb2VIV3Se5O18 (2), Pb2Nbv2Se4O16 (3), Bi2V2Se4O16 S4+ and Bi2MoVI2Se2O3)2]2 (5). The structure ot 1 textures a 3D network built by 3D anionic chains ot [V2O5(SeO3)2] - interconnected by Pb ± ions with six-membered-ring (MR) tunnelx along the b axis. The structure of 5 textures a 3D anionic framework network composed of V1"Ou octahedra corner-sharing with 5eO3 anions, with the Pb2+ ions located at the resultant 8-MR tunnels. The oxidation state ot the vanadium cation ix 4+ due to the partial oxidation ot V203 by 5e02 at high temperature. The structure ot 3 textures novel t D double chains ot [Nb2O3(SeD3)4]4 that are interconnected by Pb2+ ions, tornrin% a 3D network with t 2-MR tunnels along the cxxix. 4 textures a 3D tramework composed ot 2D layem ot [Bi2(SeD3)2] ± and 1 D [(VO2)2(SeO3)2]2 double chains. The structure ot 5 textures a 3D network composed ot bismuth(l II) selenite with large 10-MR tunnels along the a axis that are occupied by MO2O10 dimers. The results of optical diffuse-retlectance spectrum measurements and electronic structure calculations based on density tunctional theory methods indicate that all tive compoundx are wide-band-gap semiconductors. Luminescent property measurements tor compounds 1 -5 and magnetic measurements tor compound 2 were also made. [ABSTRACT FROM AUTHOR]

The preparation of a new trisodium triborate, Na3[B3O4(OH)4], and its complete characterization in terms of molecular structure and thermal behavior are reported. Synthesis of this compound was achieved either by NaBH4 hydrolysis or by thermal treatment of Na3B3O4(OH)4] 2H2O. The crystal structure was determined by singlecrystal X-ray diffraction. The trisodium triborale crystallized in the monoclinic system (a = 12.8274(6) A, b = 7.7276(4) A, C = 6.9690(3) A, and = 98.161 (3)°), space group Cc, Z= 2. The structure of Na3[B3O4(OH)4] comprised [B3O4 (OH)4]3 polyanions, based on 6-0-containing rings with two tetracoordinated boron atoms and one tricoordinated boron atom in the fragments BO 2(OH)2 and BO3, respectively. These polyanions are interconnected by four intermolecular hydrogen bonds and presented a tilt of 10.470 (4)° compared to the a axis. Thus, they are stacked by rotation of about 1800 around an axis defined by the three-coordinated boron atoms and parallel to the c axis. Such polyanions were only observed previously in two synthetic compounds, M3[B3 O4(OH)4].2H2O with M = K and Rb, which were isostructural. The originality of the present work was the synthesis and the description of a different crystallographic structure containing this polyanion. Characteristic peaks ranging from 500 to 1500 cm-1 and around 3300 cm -1 highlighted the presence of the 6-0 rings and hydroxyf groups, respectively. The decomposition temperature To 155°C was obtained by thermogravimetric analysis, and the following equivalent formula in lerms of hydration degree was proposed: NaBO2-2/3H2 O. Na3[B3O4(OH)4] decomposed into Na3[B3O5(OH)2] in equilibrium with its vapor. [ABSTRACT FROM AUTHOR]

We report that 1-(2-picofyl)-1,2,3-trtazole (dick triazole) tons stable complexes with transition-metal ions in which the coordination involves the triazole N2 nitrogen atom and the pendant 2-picotyt group. This is exemplified by model compound 1-(2-picolyl)-4-phenyt-1H-1,2,3-triazole (Lx) and its complexes wtth transition-metal ions ot PtII, PdII, CuII, RuII, and AgI. The coordination was investigated espedmentally and theoretically. Ligand Lx easily reacted at room temperature with cis-[PtCl2(DMSO)2], [Pd(CH3CN)4]BF4)2, CuCI2, [RuCl(μ-Cl)η6-p-cymene)]2, and AgNO3 to give stable chelates [PtCI2Lx] (1), [Pd(Lx)2](BF4)2 (2), [CuCl2(Lx)2] (3), [RuCI(η6-p-cymene)Lx]OTf (4), and [Ag2(Lx)2(NO3)2] (5), respectively, in 60-98% yield. The structures ot 1-5 were unambiguously confirmed by NMR spectroscopy and single-crystal X-ray diffraction analysis. Density functional theory calculations were carried out in order to theoretically investigate the stabilization factors in 1-5. A comparison ot the chelating properties ot ligand Lx was made with structurally similar and isomeric 1-(2-aminoethyt)-substituted 1,2,3-triazole (Ly) and 4-(2-aminoethyt)-substituted 1,2,3-triazole (Lz). The complexation affinity ot Lx was attributed to &#x-back-donation from the metal to the pendant pyddine side arm, whereas the stability of the complexes invoMng Ly and Lz mainly originates from efficient π-back-donation to the triazole ring. [ABSTRACT FROM AUTHOR]

Zeolites containing transition-metal ions (TMIs) often show promising activity as heterogeneous catalysts in pollution abatement and selective oxidation reactions. In this paper, two aspects of research on the TMIs Cu, Co, and Fe in zeolites are discussed: (i) coordination to the lattice and (ii) activated oxygen species. Allow loading, TMls preferably occupy exchange sites in six-membered oxygen rings (6MR), where the TMls preferentially coordinate with the O atoms of Al tetrahedra. High TMI loadings result in a variety of TMI species formed at the zeolite surface. Removal of the extralattice O atoms during high temperature pretreatments can result in autoreduction. Oxidation of reduced TMI sites often results in the formation of highly reactive oxygen species. In Cu-ZSM-5, calcination with O2 results in the formation of a species, which was found to be a crucial intermediate in both the direct decomposition of NO and N2O and the selective osidation of methane into methanol. An activated oxygen species, called α-O, is formed in Fe-ZSM5 and reported to be the active site in the partial oxidation of methane and benzene into methanol and phenol, respectively. However, this reactive α-O can only be formed with N2O, not with O2. O2-activated Co intermediates in faujasite (FAU) zeolites can selectively oxidize α-pinene and epoxidize styrene. In Co-FAU, CoIII superoxo and peroxo complexes are suggested to be the active cores, whereas in Cu and Fe-ZSM-5, various monomeric and dimeric sites have been proposed, but no consensus has been obtained. Very recently, the active site in Cu ZSM-5 was identified as a bent [Cu—O—Cu]2+ core (Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 18908—18913). Overall, O2 activation depends on the interplay of structural factors such as the type of zeolite and sizes of the channels and cages and chemical factors such as the Si/Al ratio and the nature, charge, and distribution of the charge-balancing cations. The presence of several different TMI sites hinders the direct study of the spectroscopic features of the active site. Spectroscopic techniques capable of selectively probing these sites, even if they only constitute a minor fraction of the total amount of TMI sites, are thus required. Fundamental knowledge of the geometric and electronic structures of the reactive active site can help in the design of novel selective oxidation catalysts. [ABSTRACT FROM AUTHOR]

We report the synthesis, crystal structures, and magnetic properties of two new metal-radical chains built up tram a new class at organic radical-based ligands, the polychlorinated triphenylmethyl (PTM) radicals. Crystal structures of two new 1D coordination polymers, [Cu2(PTMDC)2(py)5(∙3EtOH))-3EtOH (1) and [Co2(PTMDC)2(DMF)2(H2O)6]5DMF (2) (where PTMDC is a PTM radical functionalized with two carboxylic groups), show similar chain-like structures, in which each of the PTMDC radicals are connecting two Cu(ll) or Co(ll) metal ions. Therefore, from a magnetic point of view, both structures describe a magnetic chain model based on the PTMDC-M(ll) unit. In this manuscript, the magnetic exchange coupling constants between both metal ions and the bridging PTM radicals have been determined. In both cases, the temperature dependence of the magnetic susceptibility reveals antiferromagnetic exchange coupling constants between the PTMDC radicals and Cu(ll) (J/kB -42 K) and Co(ll) (J/kB = -14.6 K) ions based on the exchange Hamiltonian H = -JΣSA1SA1-1. [ABSTRACT FROM AUTHOR]

First-row transition metal complexes of the tris(pyrrolyl)ethane (tpe) trianion have been prepared. The tpe ligand was found to coordinate in a uniform η1,η1,η1-coordination mode to the divalent metal series as revealed by X-ray diffraction studies. Magnetic and structural characterization for complexes of the type [(tpe)MII(py)][Li(THF)4] (M: Mn, Fe, Co, Ni) reveal each divalent ion to be high-spin and have a distorted trigonal-monopyramidal geometry in the solid state. The pyridine ligand binds significantly canted from the molecular C3 axis due to a stabilizing p-stacking interaction with a ligand mesityl substituent. Cyclic voltammetry on the [(tpe)MII(py)]- series reveals a common irreversible oxidation pathway that is entirely ligand-based, invariant to the divalent metal bound. This latter observation indicates that fully populated ligand-based orbitals from the tpe construct are energetically most accessible in the electrochemical experiments, akin to their dipyrromethane analogues. Chemical oxidation of [(tpe)FeII(py)]- yields a product in which the ligand has dissociated one pyrrole (following tpe oxidation and H-atom abstraction) and binds a second equivalent of pyridine to form the neutral, tetrahedral FeII species (κ2-tpe)Fe(py)2. Similarly, chemical oxidation of the Zn(II) analogue shows evidence for tpe oxidation by electron paramagnetic resonance spectroscopy (77 K, toluene glass) with an isotropic signal for the organic radical at g = 2.002. Density functional theory analysis on this family of complexes reveals that the highest lying molecular orbitals are completely ligand-based, corroborating our proposed electronic structure assignment. [ABSTRACT FROM AUTHOR]

High-frequency electron paramagnetic resonance (HF-EPR) spectroscopy was employed to examine the oxidation slate and local structure of Ni and Mn ions in Ni,Mn-codoped LiCoO2. The assignment of EPR signals was based on Mg,Mn-codoped LiCoO2 and Ni-doped LiCoO2 used as Mn4+ and low-spin Ni3+ EPFI references. Complementary information on the oxidation state of transition-metal ions was obtained by solid-state 6.7Li NMR spectroscopy. For slightly doped oxides (LiCo1-xNixMnxO2 with x < 0.05), nickel and manganese substitute for cobalt in the CoO2 layers and are stabilized as Ni3+ and Mn4+ ions. The local structure of Mn4+ ions was determined by modeling of the axial zero-field-splitting parameter in the framework of the Newman superposition model, It has been found that the local trigonal distortion around Mn4+ is smaller in compadson with that of the host site. To achieve a local compensation of Mn4+ charge, several detect models are discussed. With an increase in the total dopant content (LiCO1-xNixMnxO2 and 0.05 ⩽ x ⩽5 0.10), a saturation in the Ni3+ amount (up to x < 0.05) is attained, while the Mn4+ content increases gradually. Ni3+ ions are surrounded by Co3+ ions only in the whole concentration range (0< x 5 0.10). The first metal coordination sphere of Mn4+ ions undergoes a transformation with an increase in the total Ni and Mn contents due to a progressive replacement of Co3+ by Mn4+ and Ni2+ ions. For highly doped oxides (LiCo1-xNixMnxO2 wilh x = 0.10), nickel and manganese achieve, with respect to the local charge compensation, their usual oxidation states of 2+ and 4+. [ABSTRACT FROM AUTHOR]

The as-piepareddouble-perovsldte Ba2LaNbO6 (space group I2/m at ambient temperatures) exhibited an unexpected well-resolved red luminescence, which was found to arise from parts-per-million impurity of Mn4+. The ions Mn4+ or Cr3+ doped into this host are situated at Nb5+ sites with slightly distorted octahedral symmetry, with the distortion greater for the case of greater charge mismatch. The Stokes luminescence spectra of the dopant ions comprise v3, v4, and v6 moiety mode vibronic origins, and the high vibrational frequency ratio v4/v3 signals the stiffness of the O-M-O (M = Mn, Cr) angle in the double perovskite. The site symmetry at the La3+ site of lanthanide Ions doped into Ba2LaNbO6 comprises a 2-fold axis at most. All dopant sins exhibit concentration quenching in this lattice. [ABSTRACT FROM AUTHOR]

The wavelength dependence of the cubic nonlinearity of ligated platinum-terminated polyynes trans,trans-((p-MeC[sub6]H[sub4])[sub3]P)2(p-MeC[sub6]H[sub4])Pt(C≡C)[subn]Pt(p-C[sub6]H[sub4]Me)(P(p-C[sub6]H[sub4]Me)[sub3])[sub2] (n 3-6, 8, 10, 12) has been examined by femtosecond Z-scan studies in the wavelength range 520-1500 nm and the results rationalized by density functional theory calculations on the model complexes trans,trans-(H[sub3]P)[sub2](C[sub6]H[sub5])Pt(C≡C)[subn]Pt(C[sub6]H[sub5])(PH[sub3])[sub2] (n = 2-8, 10, 12). Although the final states for one- and two-photon transitions are not the same in these centrosymmetric molecules, the Z-scan studies reveal coincidences in one-photon absorption with features in the frequency dependencies of both real and imaginary parts of the cubic hyperpolarizability, as well as inflections in the frequency dependencies of the real part of γ that correspond to resonances in the imaginary part of γ. The theoretical studies suggest that the linear absorption spectra are dominated by X[sup1]A[subg] → n[sup1]B[sub3u] transitions, with the first state of B[sub3u] symmetry playing a steadily diminishing role upon oligoyne chain lengthening. The theoretical studies also predict a red-shift of two-photon absorption (TPA) profile with increasing conjugation length, and a significant enhancement on proceeding from the shortest to the longest chromophore, trends that are observed experimentally. The experimental low-energy TPA maxima for these complexes can be approximated by a simple Gaussian profile. The sp-carbon chain-length dependence of linear and nonlinear absorption maxima enable an estimate (neglecting saturation) of 660 and 1000 nm for the infinite carbon chain, carbyne. [ABSTRACT FROM AUTHOR]

We have synthesized a new type of acyclic bis(N2O2 chelate) ligand that affords a C-shaped O6 site by the metalation of the N2O2 salamo sites. UV-vis titration clearly showed that complexation of H4L with MII (MnII; CoII, and NiII) affords the 1:3 complex [LM3]2+ in a cooperative fashion, whereas complexation with copper(II) gave two or more complexes in a stepwise fashion. The manganese(ll) complex [LMn3(OAc)2(MeOH)2] crystallizes in the triclinic system, space group PT, with unit cell parameters a = 9.584(6) Å, b = 13.666(9) Å, c = 15.566(10) Å, α = 1 08.702(8)°, β = 95.255(4)°, γ = 101.023(8)°, and Z = 2, and the cobalt(II) complex [LCo3(OAc)2(EtOH)2] · 2CHCl3 crystallizes in the triclinic system, space group P1, with unit cell parameters a = 13.291(6) Å, b = 13.913(7) Å, C = 14.599(8) Å, α = 88.27(2)°, β = 67.391(15)°, γ = 73.90(2)°, and Z = 2. In the crystal structures, three metal ions occupied both the N2O2 and 06 sites of the ligand L4-. The resultant trinuclear complexes have a C- or S-shaped structure depending on the metal employed. The different nature of the N2O2 and O6 sites of the ligand H4L leads to the site-selective introduction of two different d-block transition metals. An X-ray crystallographic analysis revealed the structures of the two heterotnnuclear complexes, [LZN2Mn(OAc)2(MeOH)2] and [LCu2Zn(OAc)2(H2O)]. [ABSTRACT FROM AUTHOR]

A new bis tridentate ligand 2,2′-bipyridine-3,3′-[2-pyridinecarboxamide] H2L1 which can bind transition metal ions has been synthesized via the condensation of 3,3′-diamino-2,2′-bipyridine together with 2-pyridine carbonyl chloride. Two copper(II) coordination compounds have been prepared and characterized: [Cu2(L1)(hfac)2]·3CH3CN·H2O (1) and [Cu2(L1)Cl2]·CH3CN (2). The single-crystal X-ray structures reveal that complex 1 crystallizes in the triclinic space group P1, with the unit cell parameters a = 12.7185(6) Å, b = 17.3792(9) Å, c = 19.4696(8) Å, α = 110.827(2)°, β = 99.890(3)°, γ = 97.966(3)°, V= 3868.3(3) Å3, Z = 4, R= 0.0321 and Rw = 0.0826. Complex 2 crystallizes in the monoclinic space group P21/n with the unit cell parameters a = 12.8622(12) Å, b = 9.6100-(10) Å, c = 19.897(2) Å, β = 102.027(3)°, V = 2405.3(4) Å3, Z = 4, R = 0.0409 and Rw = 0.1005. In both complexes the ligand is in the dianionic form and coordinates the divalent CuII ions via one amido and two pyridine nitrogen donor atoms: In 1, the coordination geometry around both CuII ions is best described as distorted trigonal bipyramidal where the remaining two coordination sites are satisfied by hexafluoroacetylacetonate counterions. In 2 both CuII ions adopt a (4 + 1) distorted square pyramidal geometry. One copper forms a longer apical bond to an adjacent carbonyl oxygen atom, whereas the second copper is chelated to a neighboring Cu—Cl chloride ion to afford a μ-Cl-bridged dimerized [Cu2(L1)Cl2]2 complex. The magnetic susceptibility data for 1 (2 -270 K), reveal the occurrence of weak antiferromagnetic interactions between the CuII ions. In contrast, variable-temperature magnetic susceptibility measurements for 2 reveal more complex magnetic properties, with the presence of a weak antiferromagnetic exchange (J = -10.1 K) between the copper ions in each dinuclear copper complex and a stronger ferromagnetic exchange interaction (J = 32.9 K) between the CuII ions of the Cu(μ-Cl)2Cu dimeric bridging units. [ABSTRACT FROM AUTHOR]

The use of the (NBu4)2[ReIVCl4(ox)] mononuclear species as a ligand toward divalent first row transition metal ions in the presence of imidazole affords the new trinuclear compounds of formula (NBu4)2[{ReIVCl4(µ-ox)}2MII(Him)2] [NBu4+ = tetra-n-butylammonium cation, ox = oxalate dianion, Him = imidazole; M = Mn (1), Co (2), Ni (3), Cu (4)] whose preparation, crystal structures, and magnetic properties are reported. 1-4 are isostructural complexes which are made up of discrete trinuclear [{ReIVCl4(µ-ox)}2MII(Him)2]2- anions and bulky NBu4+ cations. The Re and M atoms exhibit somewhat distorted octahedral surroundings which are built by four chloro and two oxalate oxygens (Re) and two imidazole nitrogen and four oxalate oxygen atoms (M), the central M atom being linked to the two peripheral Re atoms through bis-bidentate oxalate. The values of the Re⋯M separation across bridging oxalate vary in the range 5.646(2) (M = Ni) to 5.794(2) Å (M = Mn). Magnetic susceptibility measurements on polycrystalline samples of 1-4 in the temperature range 1.9-300 K show the occurrence of significant intramolecular antiferro- (1) and ferromagnetic (2-4) interactions. The nature and magnitude of the magnetic coupling in 1-4 are qualitatively understood through orbital symmetry considerations. [ABSTRACT FROM AUTHOR]

PhenHDO3A is a ditopic ligand featuring a tetraazacyclododecane unit substituted by three acetate arms and one 6-hydroxy-5,6-dihydro-1,10-phenanthroline group (PhenHDO3A = rel-10-[(5R,6R)-5,6-dihydro-6-hydroxy-1,10-phenantholin-5-yl)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid). This ligand was specially designed so as to obtain highly stable heteropolymetallic assemblies. PhenHDO3A has been prepared starting from phenanthroline epoxide and either a triprotected tetraazacyclododecane or tert-butyl triester of N,N′,N′-tetraazacyclododecane-triacetic acid. The latter yields PhenHDO3A in a single step. PhenHDO3A forms kinetically stable lanthanide complexes (acid-catalyzed kinetic constant kH = (1.2 ± 0.2) × 10-3 S-1 M-1) whose solution structure has been deduced from a quantitative analysis of the paramagnetic shifts and the longitudinal relaxation times of the proton nuclei of YbPhenHDO3A. The alcohol group of the dihydro-phenanthroline unit remains coordinated to the encapsulated metal ion despite the steric crowding brought about by this group. Furthermore, the complexes are monohydrated, as shown by luminescence lifetime measurements on EuPhenHDO3A solutions. Relaxivity titrations at 20 MHz clearly indicate that the phenanthroline unit of GdPhenHDO3A is available for the spontaneous formation of highly stable tris complexes with the Fe2+ and Ni2+ ions. The water-exchange times and the rotational correlation times of GdPhenHDO3A and Fe(GdPhenHDO3A)32+ have been deduced from variable temperature 17O NMR studies and from nuclear relaxation dispersion curves. Despite rather slow water-exchange rates (τm0 = 1.0–1.2 × 10-6 s), relaxivity gains of 90% have been observed upon the formation of the heterometallic tris complexes. The latter rotate about four times more slowly (τr0 = 398 ps) than the monomeric unit (τr0 = 105 ps) and their relaxivity is, accordingly, twice as high. The relaxivity of the tris complexes between 10 and 50 MHz is comparable to relaxivities reported for Gd3+-containing dendrimers of much higher molecular weights. The high relaxivity of the tris-PhenHDO3A lanthanide complexes is attributed to their internal rigidity. [ABSTRACT FROM AUTHOR]

Investigates the potential energy surfaces corresponding to the dehydration reaction of NH[sub 3] by VO[sup +] and FeO[sup +] metal oxide cations within the framework of the density functional theory in its B3LYP formulation. Use of optimized basis sets for iron and vanadium; Occurrence of the reaction through two hydrogen shifts from the nitrogen to the oxygen atom giving rise to multicentered transition states; Possible spin crossing between surfaces at different spin multiplicities.

The solid-state chelation of transition metal ions (Co[sup 2+], Ni[sup 2+,] and Cu[sup 2+]) from aqueous solutions into the lithium aluminum layered double hydroxide ([LiAI[sub 2](OH)[sub 6]]CI·0.5H[sub 2]O or LDH) which has been pre-intercalated with EDTA (ethylenediaminetetraacetate) ligand has been investigated. The intercalated metal cations form [M(edta)][sup 2-] complexes between the LDH layers as indicated by elemental analysis, powder X-ray diffraction, and IR and UV-vis spectroscopies. If metal chloride or nitrate salts are used in the reaction with the LDH then co-intercalation of either the CI[sup -] or NO[sub 3, sup -] anions is observed. In the case of metal acetate salts the cations intercalate without the accompanying anion. This can be explained by the different intercalation selectivity of the anions in relation to the LDH. In the latter case the introduction of the positive charge into LDH structure was compensated for by the release from the solid of the equivalent quantity of lithium and hydrogen cations. Time-resolved in-situ X-ray diffraction measurements have revealed that the chelation/intercalation reactions proceed very quickly. The rate of the reaction found for nickel acetate depends on concentration as ∼k[Ni(Ac)[sub 2]]³. [ABSTRACT FROM AUTHOR]

Examines the magnetic properties of the coordination polymers between transition metal ions and the radical anion of tetracyanoethylene. Identification of the anisotropic magnetic moments of rare earth ions; Occurrence of rare earth radical interaction; Antiferromagnetic coupling of gadmium ions.

Examines the properties of heterodinuclear complexes containing transition metal and lanthanide ions. Application of the heterodinuclear complexes in bimetallic catalyst designs; Observation of intramolecular ferromagnetic interaction in the complex; Magnetic behavior of the complex.

Focuses on the synthesis, structures and properties of supramolecules containing transition metal ions. Formation of a trinuclear complex; Creation of a central metal ion in a strong ligand field; Analysis on the high-spin configuration of Fe(II).