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Abstract: A new compound, LiMn2+Mn3+TeO6, was prepared by solid-state reactions and characterized by powder X-ray diffraction, redox titration, conductivity, magnetic measurements and cycling behaviour in an electrochemical cell with Li counter electrode. It is triclinic, P1, a = 5.1077(1), b = 8.5707(1), c = 5.0589(1), α = 92.515(1)°, β = 92.092(2)°, γ = 89.818(2)°, Z = 2. The structure is based on strongly distorted hexagonal close packing of oxygen anions with cations occupying octahedral voids and represents the ordered variant of orthorhombic Li2TiTeO6 structure, derived from LiSbO3. TeO6 octahedra are almost regular but all four independent MnO6 octahedra display severe distortions. Room-temperature conductivity is unexpectedly low for a mixed-valence compound, 2 × 10−7 S/cm. Together with the observed antiferromagnetic exchange interaction, this is a prerequisite for the colossal magnetoresistance effect. The unit cell volumes of LiMn2TeO6, LiSbO3, Li2M4+TeO6 and LiMM′XO6 series (a total of 21 compounds) correlate well with average cationic radii, but LiMn2SbO6 deviates considerably, and its preparation could not be reproduced. [Copyright &y& Elsevier]

We demonstrate that DFT calculations performed with the local density approximation (LDA) allow for significantly better reproduction of lattice constants, the unit cell volume and the density of Ag(II)SO than those done with generalized gradient approximation (GGA). The LDA+U scheme, which accounts for electronic correlation effects, enables the accurate prediction of the magnetic superexchange constant of this strongly correlated material and its band gap at the Fermi level. The character of the band gap places the compound on the borderline between a Mott insulator and a charge transfer insulator. The size of the band gap (0.82 eV) indicates that AgSO is a ferrimagnetic semiconductor, and possibly an attractive material for spintronics. A bulk modulus of 27.0 GPa and a compressibility of 0.037 GPa were determined for AgSO from the third-order Birch-Murnaghan isothermal equation of state up to 20 GPa. Several polymorphic types compete with the ambient pressure P-1 phase as the external pressure is increased. The P-1 phase is predicted to resist pressure-induced metallization up to at least 20 GPa. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The DFT calculations performed within local density approximation disclose conceivable existence of two novel mixed-valence Ag(I)/Ag(II) fluorides, AgF, i.e., Ag(I)Ag(II)F and AgF, i.e., Ag(I)Ag(II)F. AgF is predicted to crystallize in three equally stable NaCuF-, KAgF-, or CuTeO-type structures, while AgF should be isostructural to NaCuF. The calculated vibration-corrected energies of formation at 0 K of AgF and AgF (in their most stable polytypes) from binary fluorides are negative but small (respectively, -0.09 eV and -0.21 eV per formula unit). Formation of AgF (which, in fact, is a mixed valence Ag(I)/Ag(III) salt) from binary fluorides is much less likely, since the energy of formation is quite positive of about a quarter eV. The predicted volumes per formula unit for all forms of AgF are larger and that for KCuF-type AgF is smaller than the sum of volumes of the corresponding binary fluorides; AgF should not form at high pressure conditions due to a decomposition to the binary constituents. AgF and AgF should exhibit genuine mixed- and not intermediate-valence with quite different coordination spheres of Ag(I) and Ag(II). Nevertheless, they should not be electric insulators. AgF is predicted to be a metallic ferrimagnet with a magnetic superexchange coupling constant, J, of -2 meV while AgF should be a metallic ferromagnet with J of +52 meV. Since AgF and AgF are at the verge of thermodynamic stability, a handful of exothermic reactions have been proposed which could yield these as yet unknown compounds. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Recent results regarding the importance of tunneling-barrier heights for charge transfer between distant redox partners are reviewed. Examples include studies of photoinduced hole transfer in donor–bridge–acceptor systems, as well as work on mixed valence molecules. The barrier heights imposed by different bridging units are discussed. Key examples include the comparison of biphenyl and fluorene spacers, and the comparison of p-xylene and p-dimethoxybenzene bridging units. [Copyright &y& Elsevier]

Abstract: [(SO3)Co(cyclam)(NCS)] and [(SO3)Co(cyclam)-NCS-Ru(NH3)4(NCS)](BF4) complexes were synthesized and characterized by means of X-ray diffraction, electrochemistry, elemental analysis, and spectroscopic techniques. Crystallographic and FTIR data indicated NCS− ligand is coordinated to Co through the nitrogen atom in the monomer species. Electrochemistry and FTIR data of the material isolated after reductive electrolysis of [(SO3)Co(cyclam)(NCS)] hint that NCS− and SO3 2− are released thus forming [Co(cyclam)(L)2]2+, where L is solvent molecules. The formation of the heterobimetallic mixed-valence complex induced a thermodynamic stabilization of Co and Ru metal atoms in the oxidized and reduced states, respectively. According to the Robin and Day classification, a Class II system with a comproportionation constant of 5.78×106 is suggested for the mixed-valence complex based on the electrochemical and UV–Vis–NIR results. [Copyright &y& Elsevier]

Abstract: Absorption-based studies of low-energy atomic edges possess an inherent challenge in distinguishing surface and bulk contributions to the measured signal. The nature of the absorption process itself, being predominantly dipole in character, can also be a limiting factor in understanding electronic structure, particularly for correlated-electron systems. Non-resonant inelastic X-ray scattering (NIXS) provides a complementary means to soft X-ray absorption (XAS) methods in the study of low-energy excitations. The use of higher-energy X-rays (∼10keV) enables bulk-sensitive measurements. Modern instrumentation and synchrotron facilities permit experiments with access to transitions not only in the dipole-transition regime but also those of higher-order. Access to these non-dipole transitions provides an additional perspective into the electronic behavior of materials. Such experiments will be illustrated using rare earth materials and excitations corresponding to M, N and O edges, with emphasis on the sensitivity to 4f-occupation in cerium-based materials. [Copyright &y& Elsevier]

Abstract: NdBaFe2O5 above and below Verwey transition is studied by synchrotron X-ray powder diffraction and Mössbauer spectroscopy and compared with GdBaFe2O5 that adopts a higher-symmetry charge-ordered structure typical of the Sm–Ho variants of the title phase. Differences are investigated by Mössbauer spectroscopy accounting for iron valence states at their local magnetic and ionic environments. In the charge-ordered state, the orientation of the electric-field gradient (EFG) versus the internal magnetic field (B) agrees with experiment only when contribution from charges of the ordered d xz orbitals of Fe2+ is included, proving thus the orbital ordering. The EFG magnitude indicates that only some 60% of the orbital order occurring in the Sm–Ho variants is achieved in NdBaFe2O5. The consequent diminishing of the orbit contribution (of opposite sign) to the field B at the Fe2+ nucleus explains why B is larger than for the Sm–Ho variants. The decreased orbital ordering in NdBaFe2O5 causes a corresponding decrease in charge ordering, which is achieved by decreasing both the amount of the charge-ordered iron states in the sample and their fractional valence separation as seen by the Mössbauer isomer shift. The charge ordering in NdBaFe2O5+w is more easily suppressed by the oxygen nonstoichiometry (w) than in the Sm–Ho variants. Also the valence mixing into Fe2.5+ is destabilized by the large size of Nd. The orientation of the EFG around this valence-mixed iron can only be accounted for when the valence-mixing electron is included in the electrostatic ligand field. This proves that the valence mixing occurs between the two iron atoms facing each other across the structural plane of the rare-earth atoms. [ABSTRACT FROM AUTHOR]

Abstract: The new compound YbGe2.83 was obtained from the reaction of Yb and Ge in liquid indium. The crystal structure of YbGe2.83 adopts the trigonal, P3̄m1 space group with a=b=8.3657(12)Å and c=7.0469(14)Å. The structure of YbGe2.83 is a variant of the CaAl2Si2 structure type with ordered vacancies. Germanium atoms form double layers of puckered hexagons creating slabs that sandwich the Yb atoms. YbGe2.83 can be classified as a Zintl compound with the formula Yb(2+x)+(Ge2.83)(2+x)−. The deficiencies at the Ge sites cause a mixed/intermediate valent state of ytterbium (Yb2.35+). Valence bond sum calculations suggest an average valence of Yb ions in YbGe2.83 of 2.51 consistent with an intermediate valence compound. [ABSTRACT FROM AUTHOR]

Abstract: In this Letter we analyze the peculiarities of the Faraday rotation in the imperfect spinel type crystals for which the lattice irregularities are represented by the mixed valence clusters of transition metal ions. A such kind of complex system with the electronic configuration (for example, ) is considered in detail. The model takes into account the cubic and low symmetry crystal fields acting on the metal ions, migration of the “extra” hole as well as the orientational degeneracy (hidden optical anisotropy). The electric dipole transitions in these types of clusters with migrating hole coupled to the spin core through the double exchange mechanism are shown to lead to a significant magnetooptical activity in the visible range of spectrum. The intensity of these transitions can be comparable or higher than those for the magnetic dipole ones in the same range of frequencies. The electric dipole mechanism of the magnetooptical effects manifests itself in a highly anisotropic character of the spectra. [Copyright &y& Elsevier]

Abstract: Samarium atoms exist in two different electronic configurations, namely, divalent (Sm2+) and trivalent (Sm3+). Up to now, those two electronic configurations have been connected with the existence of Sm atoms in different valence states. Recent theoretical calculations performed by Yakovkin show that both electronic configurations have similar LDOS around the Fermi level, and as a result, should give a similar photoelectron emission in the valence band region, which was identified earlier as the emission from the Sm2+ state. The Sm3+ signal in photoelectron emission could originate from contaminations of Sm by other elements, e.g. oxygen. To check the influence of O on the electronic structure of Sm, the XPS experiments of coadsorption of O and Sm have been performed. [Copyright &y& Elsevier]

In the case of mixed-valence systems whose spin states are situated in the spin crossover region, new types of conjugated phenomena coupled with spin and charge are expected. From this viewpoint, we have investigated the multifunctional properties coupled with spin, charge and photon for the organic-inorganic hybrid system, A[FeIIFeIIIX3](A = (n-CnH2n+1)4N, spiropyran; X = dto(C2O2S2), tto(C2OS3), mto(C2O3S)). A[FeIIFeIII(dto)3] and A[FeIIFeIII (tto)3] undergo the ferromagnetic phase transitions, while A[FeIIFeIII(mto)3] undergoes a ferrimagnetic transition. In (n-CnH2n+1)4N [FeIIFeIII(dto)3](n = 3,4), a new type of phase transition called charge transfer phase transition (CTPT) takes place around 120 K, where the thermally induced charge transfer between FeII and FeIII occurs reversibly. At the CTPT, the iron valence state dynamically fluctuated with a frequency of about 0.1 MHz, which was confirmed by means of muon spin relaxation. The charge transfer phase transition and the ferromagnetic transition for (n-CnH2n+1)4N[FeIIFeIII(dto)3] remarkably depend on the size of intercalated cation. In the case of (SP)[FeIIFeIII(dto)3](SP = spiropyran), the photoinduced isomerization of SP under UV irradiation induces the charge transfer phase transition in the [FeIIFeIII(dto)3] layer and the remarkable change of the ferromagnetic transition temperature. In the case of (n-CnH2n+1)4N[FeIIFeIII(mto)3](mto = C2O3S), a rapid spin equilibrium between the high-spin state (S = 5/2) and the low-spin state (S = 1/2) at the FeIIIO3S3 site takes place in a wide temperature range, which induces the valence fluctuation of the FeS3O3 and FeO6 sites through the ferromagnetic coupling between the low spin state (S = 1/2) of the FeIIIS3O3 site and the high spin state (S = 2) of the FeIIO6 site. [ABSTRACT FROM AUTHOR]

The Bardeen-Cooper-Schrieffer (BCS) model explains superconductivity (SC) as due to correlation between electronic momentum and nuclear momentum (phonons) in a free electron gas. The BCS model lacks chemical specificity, however, since the coupling mechanism is left unspecified. After the discovery of high TC superconductivity in 1986 it was concluded that electron–phonon interactions are insufficient to explain electron pairing. A large part of theoretical research has since been aiming at finding another mechanism that would allow us to consider the superconducting system as a gas of charged free bosons. However, there appears to be no reason to assume free electrons in oxides. In this article the free-electron criterion is therefore replaced by the criterion that a pair of electrons can move freely between sites without resistance, i.e., without activation energy. Electron pair transfer is treated in a many-electron real space approach using standard mixed-valence theories. Mott-Hubbard-U is strictly defined, its dependence on breathing mode coordinates analyzed, and the connection between U and the energy gap for superconductivity clarified. d-wave gap anisotropy is found to be consistent with the general atomic level model presented here. Softening of phonon half-breathing modes in inelastic neutron scattering (INS) is connected to mixed-valency. The fundamental vibronic interaction between spin density wave (SDW) and charge density wave (CDW) states leads to a new phase with energy gap and electron pair carriers that can only be the superconducting phase. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

Abstract: The reaction of 2,6-diethyl-4,8-dimethyl-s-indacenyl-dilithium (Li2Ic′) with [Cp*RuCl]4 gives the organometallic binuclear bis-pentamethylcyclopentadienyl-ruthenium-s-indacene complex, [{Cp*Ru}2Ic′] (1, Ic′=2,4-diethyl-4,8-dimethyl-s-indacene), in high yields. The subsequent oxidation of 1 with a ferricinium salt ([Fc]+[BF4]−) gives the mixed valence compound [{Cp*Ru}2Ic′]+[BF4]− (1 +). Compound 1 was structurally characterized by X-ray crystallography, finding that both {Cp*Ru} fragments are coordinated to opposite sites of the Ic′ ligand. The structural and electronic features of 1 and 1 + have been rationalized by Density Functional Theory (DFT) calculations, which suggest that both metallic centers get closer to the Ic′ and subtle electronic reorganizations occurs when chemical oxidation takes place. Cyclic voltammetry and ESR experiments suggest a high electronic interaction between the metallic centers mediated by the Ic′ bridging ligand. Time dependent DFT (TD-DFT) calculations were carried out to understand and assign the intervalence band present in the mixed-valent specie (1 +). The main achievement of this article is to feature the relationship of the experimental data with the computational results obtained with the Amsterdam Density Functional package (ADF). Both experimental and theoretical facts demonstrate that the mixed valence system (1 +) is a delocalized one, and it can be classified as a Class III system according to the Robin & Day classification. [Copyright &y& Elsevier]

Abstract: The purpose of this review is to examine the fundamental differences between intermolecular self-exchange vs. intramolecular ET in mixed-valence complexes based on similar triruthenium structural units. The role of orbital overlap between ancillary ligands of the electron donor and acceptor are considered in self-exchange reactions which are found to be strongly adiabatic and again in bridged mixed-valence systems. The method of infrared (IR) reflectance spectroelectrochemistry for the determination of extremely fast (1011–1013 s−1) ET rate constants is reviewed as a tool to provide quantitative information about the time scales of localization and delocalization. The role of internal vibrations of the bridging ligand in strongly delocalized mixed-valence ions is investigated by resonance Raman and IR spectroscopies. The role of solvent dipolar relaxation times in determining the rates of ultrafast intramolecular ET reactions is reviewed in the context of inorganic mixed-valence chemistry. Finally, the concept of Robin–Day Class II/III “borderline” complexes is considered, and a concise definition of the localized to delocalized transition is provided in terms of the relative contributions of external solvent and internal complex ion vibrational modes to ET. [Copyright &y& Elsevier]

Reaction of Co(OAc)2 · 4H2O with N-(2-hydroxybenzyl)salicylaldimine (H2La) in dimethylformamide (DMF)-H2O yields a linear trinuclear mixed valence complex [CoIII(μ-La)(μ-Lb)(μ-OAc)]2CoII · 2DMF (1). Here, HLb is salicylaldimine, which is afforded by an in situ transformation of H2La via cleavage of the C-N bond. Complex 1 has been characterized by X-ray crystallography as well as elemental analysis, UV-Vis, and IR spectroscopy. The cathodic and anodic responses of 1 in DMF appeared at -1.46 V (CoIII → CoII, quasi-irreversible) and +0.99 V (CoII → CoIII, irreversible) versus saturated calomel electrode, respectively. The magnetic behavior of 1 has been analyzed by the one-ion approximation with spin-orbit coupling in Oh symmetry giving λ = -121 cm-1. [ABSTRACT FROM AUTHOR]

Abstract: Two batches of poly-crystalline lithium manganate were prepared by a fuel assisted solution combustion method. LiMn2O4(S) was prepared using starch as the fuel and LiMn2O4(P) was prepared using poly vinyl alcohol (PVA) as the fuel. XRD studies indicated a significant and consistent shift in the 2θ values of all the hkl peaks to higher values in LiMn2O4(P) compared to LiMn2O4(S) indicating a lattice contraction in the former. TG/DTA studies indicated a higher formation temperature (∼25°C higher) for LiMn2O4(P). The higher formation temperature most likely promotes the oxidation of some Mn3+ to Mn4+ with a lower ionic radius causing a lattice contraction. This hypothesis is confirmed through XPS studies which indicated the presence of a higher fraction of Mn4+ in LiMn2O4(P) than that present in LiMn2O4(S). A crystal shape algorithm was used to generate the crystal habits of lithium manganate from their XRD data leading to an understanding on the exposed hkl planes in these materials. From the atomic arrangement on the exposed hkl planes it is predicted that LiMn2O4(P) would be less prone to manganese dissolution and hence would possess a higher cycle life when compared to LiMn2O4(S). [Copyright &y& Elsevier]

Abstract: Homobimetallic systems where the metals are linked through a pentalenediide ligand, of the type anti-[Pn{M(CO)3}2] (Pn=pentalenediide), which include transition metals of the group VII with M= 25Mn (1), 43Tc (2), 73Re (3) and 107Bh (4), and the syn-[Pn{M(CO)3}2] isomer with M= 25Mn (s1), 43Tc (s2), 73Re (s3) and 107Bh (s4), were studied with relativistic all-electron density functional (DFT) calculations, including spin-orbit (SO) coupling via the two components ZORA Hamiltonian. The electronic structure was studied in detail in the four systems. Broken symmetry calculations were performed for all the paramagnetic systems to verify their mixed-valence character. The infrared (IR) spectra were obtained at the scalar relativistic regime and the UV–Vis was obtained by time-dependent spin-orbit DFT and compared against the experimental data available (only for 1 and 3). The relative binding energy calculations predict that the not yet reported s1, 2, s2, 4 and s4 complexes may be synthesized. Their optical and vibrational properties are described here. Due to the relativistic indirect effect acting on metal d orbitals there is an increased overlap between the nd and 2π∗ empty carbonyl orbitals, and hence the backbonding effect increases from 1/s1 to 4/s4. The calculated spin-dependent properties of the anionic complexes reveals that the isotropic g tensor decreases down the group, showing that the quenching of the total angular momentum of the unpaired electron increases along the group. [Copyright &y& Elsevier]

The optical absorption spectrum and resonance Raman enhancement of the lowest energy absorption band of K+7,7,8,8-tetracyanoquinodimethane- (TCNQ) are reported and examined in the mixed valence (MV) framework. The absorption spectrum is assigned, in accordance with previous work, using Koopmans-based calculations and the neighboring orbital model is constructed from the adiabatic orbital energies. Calculated fits of the lowest energy absorption band and the corresponding resonance Raman enhancement profiles are made using the time-dependent theory of spectroscopy. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The tetranuclear and pentanuclear mixed-valence coordination compounds Na[(NC)5FeII-μ(CN)-PtIV(NH3)4-μ(NC)-FeII(CN)4-μ(CN)-RuIII(NH3)5], or FePtFeRu, and [RuIII(NH3)5-μ(NC)-FeII(CN)4-μ(CN)-PtIV(NH3)4-μ(NC)-FeII(CN)4-μ(CN)-RuIII(NH3)5](OSO2CF3)2, or RuFePtFeRu, were synthesized and characterized by IR and UV–Vis spectroscopy, electron microprobe analysis (EPMA), inductively coupled plasma (ICP), and cyclic voltammetry (CV). Both molecules exhibit FeII →PtIV intervalent charge transfer (IVCT) absorptions in the 400–450nm range and FeII →RuIII transition(s) between 750 and 950nm. The energies, intensities, and half-widths of these transitions correspond well with those of model compounds. The cyclic voltammogram of FePtFeRu between 0.00 and 0.90V versus SCE exhibits two quasi-reversible Fe waves at 0.56 and 0.74V versus SCE, while that for RuFePtFeRu has only one Fe redox event at 0.72V versus SCE. When the potential of the working electrode is scanned negative of −0.38V versus SCE, however, both complexes undergo an ECE (electrochemical–chemical–electrochemical) mechanism whereby the electrochemical reduction of Ru(III) is followed by a double electron transfer to reduce Pt(IV) to Pt(II). Upon reduction to Pt(II), the cyanide bridges break and the complexes dissociate into smaller fragments. Irradiation of the FeII →PtIV IVCT transition in both compounds leads to a photolysis solution that contains dissociated Fe(II)–Ru(III) as one of its products. Irradiation of the FeII →RuIII IVCT transition yields a similar UV–Vis spectrum, suggesting that the same intermediate is common to both photolysis mechanisms. The implications of this research within the larger context of multiple electron transfer are also discussed. [Copyright &y& Elsevier]

The Pd-Pt(111) and the Ce-Pd-Pt(111) overlayer systems were studied by X-ray photoelectron spectroscopy and low-energy electron diffraction (LEED). Variations in the work function were measured by ultraviolet photoelectron spectroscopy. The Pd overlayer thicknesses were in the range of 1 to 4 monolayers (MLs). The Ce overlayer thicknesses were in the range is of 0.5 to 1.5 MLs. The interfaces were studied for annealing temperatures up to 700°C. Surface alloying or intermixing of Ce, Pd and Pt was observed. Upon deposition at ambient temperatures, Ce forms an overlayer. During annealing, both Pd and Ce were found to dissolve into the Pt substrate. For a Pd coverage of about 1 ML, the Ce-Pd-Pt(111) system was found to be Pt, terminated after annealing to 700°C. For Pd coverage above 1 ML, both Pd and Pt were found to be present at the surface. Cerium was found to be absent from the top surface layer in both cases. [ABSTRACT FROM AUTHOR]

• This paper correlates the magnetic transitions with the temperature dependent Raman Measuremnts. • Mixed valency of Mn is observed in both the synthesized doped manganite. • The Magnetization-Temperature (M-T) reveals the three transition: Paramagnetic to ferromagnetic (P-F) around 275 K, Charge ordered transition (CO) around 140 K and Spin –Glass (SG) around 40 K. The manuscript reports temperature-dependent magnetic transitions correlated to variations in the phonon modes in Nd 1−x Sr x MnO 3. Synthesis of x = 0.4 & 0.5 compounds by the solid-state reaction method was followed by structural/microstructural and electronic characterizations. The crystal structure of both compositions is orthorhombic with Pbnm symmetry, as confirmed by x-ray diffraction. The XPS data confirm the mixed Mn valance with the desired stoichiometry. The phase-separated nature is manifested through the occurrence of various phases, e.g., spin-glass (SG), charge order (CO), ferromagnetic (FM), and paramagnetic (PM), as the temperature is varied from 20 to 300 K. The temperature-dependent Raman measurements reveal that although the material is structurally stable in the studied temperature range of 80–440 K, noticeable discontinuities in the phonon mode shifts were noticed. These phonon mode shifts are found to directly correspond to the magnetic transitions. The change in the frequency of the Raman modes with temperature, which causes the observed shift, could be attributed to various factors such as lattice expansion, anharmonic interactions, spin-phonon coupling, electron-phonon interaction, etc. Here, we have used spin-phonon coupling along with lattice expansion as well as anharmonic interactions to describe the behavior of modes in the FM regime and lattice expansion and anharmonic interaction in the PM phase. [ABSTRACT FROM AUTHOR]

The heteronuclear MM quadruply bonded oxalate bridged compound [(t-BuCO2)3MoW]2(µ-C2O4) (I) has been prepared from the reaction between MoW(O2Ct-Bu)4 and oxalic acid and characterized by elemental analysis, 1H NMR and UV-vis spectroscopy, and electrochemical studies. Single electron oxidation of I by reaction with Ag+PF6– leads to the formation of the kinetically labile radical cation I+, which has been characterized by UV-vis, NIR, and EPR spectroscopy. The latter results are compared with the properties of their related homonuclear Mo4- and W4-oxalate bridged compounds and their respective radical cations. The spectroscopic features of the related radical cations [(t-BuCO2)6MoxWy(µ-C2O4)]+, where x = 1, 2, 3 and y = 4 – x, are also described with the conclusion that the [(t-BuCO2)3Mo2(µ-C2O4)W2(O2Ct-Bu)3]+ and [(t-BuCO2)3Mo2(µ-C2O4)MoW (O2Ct-Bu)3]+ cations are valence trapped on the Robin and Day scheme for the classification of mixed valence compounds. [ABSTRACT FROM AUTHOR]

Abstract: A series of heterobimetallic η6-[(ferrocenyl)indene]-Cr(CO)3 complexes differing for the position of the ferrocenyl group, 1-(ferrocenyl)indene and 2-(ferrocenyl)indene, and the degree of indene methylation (tetramethyl- and hexamethyl-) have been prepared and studied with the aim to stabilise the mono- and dications generated by chemical and electrochemical oxidation, and at same time to tune the metal–metal electronic coupling in the mixed-valence cations. The magnitude of electronic delocalisation and spin density in the cations have been monitored by means of optical techniques (UV–Vis, near-IR, mid-IR) and EPR spectroscopy. The results have been rationalised in the framework of Marcus-Hush theory and at quantum chemistry level by DFT and TD-DFT methods, establishing that a metal-to-metal electronic coupling occurs the magnitude of which depends on the degree of indene methylation. [Copyright &y& Elsevier]

Abstract: Two novel three-dimensional vanadium phosphites |(C10H10N2)| 1 and |(C4H16N3)| 2 have been synthesized hydrothermally in the presence of structure-directing agents. Single-crystal structural analysis reveals that compound 1 has a three-dimensional open-framework with two different types of intersecting channels (monoclinic, P21/n, a =6.3541(14)Å, b =10.460(2)Å, c =14.769(3)Å, β =90.412(5)o, V =981.6(4)Å3, Z =2 with R 1 =0.0523), while compound 2 (orthorhombic, Pbca, a =13.612(3)Å, b =9.5753(19)Å, c =14.022(3)Å, V =1827.6(6)Å3, Z =4 with R 1 =0.0441) presents a three-dimensional open-framework that consists of a novel {V3O14F2} trimer with mixed valence linked by two bridging F atoms. In addition, it is worth noting that the organic templates play important roles in the formation of both novel structures. Further characterization of the two compounds has been performed, including X-ray powder diffraction, ICP, CHN, IR and TG–DTA analyses. [Copyright &y& Elsevier]

The crystal structure of the mineral picotpaulite, TlFe2S3, was solved and refined using single-crystal X-ray diffraction data collected at room temperature. The symmetry is orthorhombic, space group Cmcm, with unit-cell parameters: a = 9.083(6), b = 10.754(6), c = 5.412(4) Å, V = 528.6(6) Å3, Z = 4. The structure was refined to the conventional R factor 0.0532 for 226 independent reflections with I > 2σ(I) and 21 variables. Picotpaulite is isostructural with minerals rasvumite (KFe2S3) and pautovite (CsFe2S3), as well as with a number of synthetic compounds belonging to the CsCu2Cl3 structure type. The structure consists of double chains of FeS4-tetrahedra running along [001] interconnected by TlS10 coordination polyhedra, which form zig-zag chains along the same direction. The Fe-Fe distances between neighbours along the chain direction and perpendicular to it are 2.706(2) and 2.693(6) Å, respectively, indicating strong Fe-Fe interactions. The average oxidation state of Fe is +2.5, achieved by electron transfer over the close Fe sites. Thallium coordination polyhedron can be described as a combination of a square antiprism adjacent to a trigonal prism. The 6s² electrons of Tl behave as an inert pair and the atom is situated in the centroid of its coordination. [ABSTRACT FROM AUTHOR]

We present the first study of the phonon density-of-states (DOS) of mixed-valent (m.v.) Eu metal in the bcc-phase at 10 GPa and in the hcp-phase at 17 GPa using 151Eu nuclear inelastic scattering of synchrotron radiation. In both cases, features in the phonon-DOS exhibit shifts to lower energies when compared with stable divalent or trivalent rare-earth metals with larger molar volumes. These anomalous properties are caused by the strong m.v. state of Eu in both phases, determined independently by 151Eu nuclear forward scattering, and are discussed in conjunction with a recent study of the Sm phonon-DOS in divalent and m.v. SmS. [ABSTRACT FROM AUTHOR]

The electrochemistry of [Cu(OEP)] and [Ni(OEP)] are compared with the mixed-valence π-cations [Cu(OEP)ꔷ/2]2+ and [Ni(OEP)ꔷ/2]2+. These electrochemical studies, carried out with cyclic voltammetry and hydrodynamic voltammetry, show that the mixed valence π-cations have distinct electrochemical properties, although the differences between the [M(OEP)]+/0 and [M(OEP)ꔷ/2]2+/0 processes are subtle. [Copyright &y& Elsevier]

Abstract: Reaction of Mn(II) with phenoxyalkanoic acids and di-2-pyridyl ketone oxime (Hpko) leads to neutral tetranuclear complexes of the general formula Mn4(O)(pko)4(phenoxyalkanoato)4 (phenoxyalkanoic acids: H-mcpa=2-methyl-4-chloro-phenoxy-acetic acid, H-2,4,5-T=2,4,5-trichloro-phenoxy-acetic acid or H3,4-D=3,4-dichloro-phenoxy-acetic acid). The compounds were synthesized by adding di-2-pyridyl ketone oxime to MnCl2 in the presence of the sodium salts of the alkanoic acids in methanol. The crystal structure of Mn4(II/II/II/IV)(O)(pko)4(2,4,5-T)4 ·2.5CH3OH·0.25H2O 1 shows that the complex consists of a [Mn4(μ4-O)]8+ core with a Mn(IV) and 3 Mn(II) ions in octahedral environment and a μ4-O atom bridging the four manganese ions. Spectroscopic studies of the interaction of these tetranuclear clusters with DNA showed that these compounds bind to dsDNA. The binding strength of the Mn4(II/II/II/IV)(O)(pko)4(2,4,5-T)4 complex for calf thymus DNA is equal to 1.1×104 M−1. Among the deoxyribonucleotides they bind preferentially to deoxyguanylic acid (dGMP). Competitive studies with ethidium bromide (EthBr) showed that the Mn4(II/II/II/IV)(O)(pko)4(2,4,5-T)4 complex exhibited the ability to displace the DNA-bound EthBr indicating that the complex binds to DNA via intercalation in strong competition with EthBr for the intercalative binding site. Additionally, DNA electrophoretic mobility experiments showed that all three complexes, at low cluster concentration, are obviously capable of binding to pDNA causing its cleavage (relaxation) at physiological pH and temperature. At higher cluster concentration, catenated dimer forms of pDNA was formed. [Copyright &y& Elsevier]

Abstract: The 119Sn Mössbauer spectra have been measured for the intermediate valent CeSn3 (stoichiometric) and CeSn3.1 (slightly non-stoichiometric) high-quality single crystals in the temperature range from 300 to 30K with an aim to look into the local surrounding of the Sn site and its valence state in these crystals. The spectra clearly indicate a para-magnetic ground state throughout the temperature range. Two different doublets with a quadrupole interaction that we associate with two different paramagnetic S1 and S2 sites, result from our first attempt to fit the experimental spectra, the ratio between these sites S1/S2 being around 3/1. The magnitudes of isomer shift reveal a 2+ valence state for the Sn, that does not show any change for either the S1 or the S2 sites, in the whole investigated temperature range. The different values of quadrupole splitting ΔE Q for S1 and S2 again confirm that the Sn atoms have different atomic coordinations. [Copyright &y& Elsevier]

Abstract: The mixed valence (MV) phenomenon has been observed so far in a large number of various compounds but containing only lanthanides. These properties are usually associated with the mixing of the localised f-state and the band states. The usual valence state for magnetic uranium intermetallics is the trivalent state 5f3 or hybridised 5f2 6d1, both are nearly degenerate in energy and can compete for a stability of the compound. In some cases a gain in an energy minimum may be achieved by very fast fluctuating between these two states with a time of 10−14 s, which does not allow to yield the ordered state even if the exchange interactions (favourite the U–U distances) would be able for that. The latter cases seem to concern the described here intermetallics: one ternary compound based on Co, UCoGa5, and the two uranium ternary compounds based on Ru, namely U2Ru2Sn and U2RuGa8 which all crystallize in a tetragonal unit cell. All these compounds show a maximum in their temperature dependences of the magnetic susceptibility measured along and perpendicular to the c-axis. Such a behaviour, which is reminiscent of a number of Ce, (Sm, Eu) and Yb compounds for which χ(T) has in the past been considered by Sales and Wohlleben (SW) by applying their ICF model or by Lawrance et al. following their scaling procedure. It turned out that these phenomenological models can also be applied to the considered here two Ru-based uranium ternaries from which some reliable energy parameters could be found. In order to further support the mixing valence scenario for the first such cases in uranium compounds presented here, the transport and thermodynamic properties are also discussed. However, some of the most important results confirming the MV state, e.g., in U2RuGa8, has recently been achieved from the inelastic neutron scattering performed in the Rutherford Appleton Laboratory on the ISIS facility. From these measurements a characteristic gap of 60meV has been estimated in the magnetic spectrum of this compound. [Copyright &y& Elsevier]

Abstract: The studies of the thermoelectric power and band structure calculations for CeNi4Si are reported. These studied are supported by magnetic susceptibility, electrical resistivity, specific heat and X-ray photoemission spectroscopy measurements. CeNi4Si is paramagnetic down to 2K and follows the Curie–Weiss law with μ eff =0.52μ B/f.u. and the paramagnetic Curie temperature θ P =−2K. This effective paramagnetic moment is lower than the free Ce3+ value. The obtained values for the f occupancy n f and for the coupling Δ of the f level with the conduction states are in good agreement with the values found for mixed valence compounds. Below the Fermi energy the total density of states contains mainly the d states of Ni atoms. The narrow peaks of the f states of Ce atoms were found above the Fermi level. CeNi4Si is characterized by γ =16mJmol−1 K−2 and θ D =335K. [Copyright &y& Elsevier]

Abstract: Two new geometrical isomers of [Cr(py)2(chrySQ)(chryCat)] (chrySQ=chrysenesemiquinonate; chryCat=chrysenecatecholate; py=pyridine) were synthesized by two different synthetic procedures. In the first, an acetonitrile solution containing a stoichiometric mixture of Cr(CO)6, chrysenequinone and pyridine was photolyzed with a Hg-lamp. The second procedure was based on substituting one of the chrysenesemiquinonate ligand in the tris-[Cr(chrySQ)3] complex with two pyridine ligands. In both procedures two isomeric forms of [Cr(py)(chrySQ)(chryCat)] were isolated with the trans-isomer obtained in higher yield. The structures of the two isomers have been modeled using parameterized PM3 semiempirical method. Theoretical harmonic vibrational frequencies of the cis- and trans-isomers have been computed and compared with the experimental vibrational frequencies. Variable-temperature magnetic susceptibility has been studied for the two isomers in the 10–300K temperature range. Theoretical modeling of the magnetic data indicated strong antiferromagnetic exchange interaction between CrIII (S =3/2) and chrySQ (S =1/2) with J =−365±6 and −395±4cm−1 for the cis- and trans-isomers, respectively. The electrochemical behavior of cis- and trans-[Cr(py)2(chrySQ)(chryCat)] complexes were studied by cyclic voltammetry in acetonitrile solvent. Both complexes showed two one-electron redox processes attributable to reversible reduction and oxidation of the chrySQ and chryCat ligands. Reduction of the Cr(III) to Cr(II) was observed for both complexes near−1300mV. The electronic spectra of the two isomers were dominated by charge-transfer (LMCT, MLCT and ILCT) transitions. In addition, a low-energy intervalence charge-transfer (IVCT) transition was observed for the cis-isomer at 1085nm. Theoretical studies of the electronic spectra by ZINDO/S-CI method were useful in interpreting the observed electronic transitions. [Copyright &y& Elsevier]

Abstract: The use of ferrocene-1,1′-dicarboxylic acid (fdcH2) in Mn cluster chemistry has led to a family of ferrocene-rich Mn7, Mn8 and Mn13 clusters. The complexes are all mixed-valence. Solid-state DC and AC magnetic susceptibility studies have established the Mn7, Mn8 and Mn13 complexes to possess S =2, 5 and 9/2 ground states, respectively. [Copyright &y& Elsevier]

Temperature dependence of the specific heat for CeNi4Si was analyzed. These studies were supported magnetic susceptibility, electrical resistivity and X-ray photoemission spectroscopy measurements. CeNi4Si is paramagnetic and follows the Curie-Weiss law with μeff = 0.52 μB/f.u. and θp = -2 K. This effective paramagnetic moment is lower than that for the free Ce3+. The f-occupancy nf and coupling A between the f level and the conduction state are derived to be about 0.91 and 36 meV, respectively. Both susceptibility data and the XPS spectra have shown that Ce ions are in intermediate valence state. The specific heat has been analyzed considering the electronic contribution, the Schottky anomaly, and the lattice contributions within the Debye model. The scheme of the energy levels created by the crystal electric field split is determined from the Schottky contribution to the specific heat. [ABSTRACT FROM AUTHOR]

The Rieske-type [2Fe&bond;2S] cores of electron-transfer (ET) proteins in the mitochondrial respiratory chain have unusual properties, such as redox potentials and spectroscopy. In this study, part IV of a series, the inherent molecular structures and characteristic electronic structures of the Rieske-type [2Fe&bond;2S] clusters are investigated using broken-symmetry hybrid density functional theory (BS-HDFT). Geometry optimizations for the oxidized and reduced states were performed and their characteristic vibrational modes are assigned. Magnetic properties are investigated using model Hamiltonians to describe the electron delocalization and the unsymmetric property. The parameters of the model Hamiltonian, such as exchange coupling J, valence delocalization B, and potential energy difference Δ, are evaluated from the BS-HDFT calculations. The valence localization and excitation energy (ΔE) of the Rieske-type [2Fe&bond;2S] cluster are discussed. The chemical bond nature is characterized by chemical indices from natural orbital analysis. Our theoretical results are reasonably consistent with experimental results. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [ABSTRACT FROM AUTHOR]

Abstract: Perovskite oxides LaTi1−x Li x O3 (x =0.2, 1/3) were synthesized using high-pressure and high-temperature method. This new synthesis route has some advantages. XRD analysis showed that the x =0.2 sample belongs to cubic perovskite-type structure and the x =1/3 sample belongs to orthorhombic perovskite-type structure. EPR measurement indicated that Ti ions were in mixed valence of +3 and +4. IR measurement indicated that the vibration frequency and width of BO6 octahedron stretching vibration absorption band decreases with the increasing of x. Valence of Ti ions can be altered by high-pressure and high-temperature. [Copyright &y& Elsevier]

Abstract: The preparation and characterization by spectroscopic and electrochemical techniques of new dinuclear complexes of the type [(tpm)(bpy)RuII(L)RuII/III(NH3)5]4+/5+ (bpy=2,2′-bipyridine), tpm=tris(1-pyrazolyl)methane, L=pz (pyrazine), 4,4′-bpy (4,4′-bipyridine), BPE (trans-1,2-bis(4-pyridyl)ethylene) and PCA (=4-pyridinecarboxaldehyde azine), are described in this work. The analysis of the visible spectral data for the metal-to-metal charge transfer (MMCT) bands in the corresponding mixed-valent species (Rub =Ru bonded to bpy; Rua =Ru bonded to NH3) allows the determination of the reorganization energies λ and electronic coupling elements H AB for the intramolecular electron transfers mediated by L. An increased transmission of the metal-to-metal electronic interaction is disclosed for this series, when comparing the distance dependence of H AB to that of the analogous series with trpy (2,2′:6′,2″-terpyridine) acting as a spectator ligand instead of tpm. [Copyright &y& Elsevier]

Abstract: 151Eu and 57Fe Mössbauer spectroscopy, differential scanning calorimetry, and high-intensity high-resolution synchrotron powder diffraction were used to determine the extent of long- and short-range charge ordering below the first-order Verwey-type transition in , the oxygen content of which was homogenized by annealing in sealed ampoule. The diffraction gives 0.68(5) valence unit of charge separation at 100K. Interpretation of this value as 68% of iron being long-range charge ordered correlates with the total transition entropy per formula of about 0.7 of the theoretical value that would be valid for all iron atoms being fully charge ordered. For long- and short-range order combined, 57Fe Mössbauer spectroscopy suggests that about 90% of iron atoms occur as charge-ordered integer and . The residual 10% are the and that did not find the way to order. Local oxygen non-stoichiometry defects that revert the direction of the charge order are suggested as one of the origins of the short-range charge order. Accordingly, the long-range charge order seen by diffraction is highest in the portion of the sample that converts last upon heating, having the most ideal valence ratio. [Copyright &y& Elsevier]

Abstract: Mixed-valence exhibits a robust Verwey-type transition. The trend in the volume change suggests a first-order transition up to the nonstoichiometry level of about . 57Fe Mössbauer spectroscopy, differential scanning calorimetry and synchrotron X-ray powder diffraction are used to study the valence mixing and charge ordering in as a function of the nonstoichiometry parameter w. 151Eu Mössbauer spectroscopy is used as a selective probe into the ferromagnetic valence-mixing coupling along c above the Verwey transition, and reveals that increasing w destroys this coupling in favor of a G-type magnetic order in parallel with the progressive removal of the valence-mixed iron states accounted for by 57Fe Mössbauer spectroscopy. This removal proceeds according to a probability scheme of mixing between ferromagnetically coupled divalent and trivalent neighbor iron atoms along c across the R layer. In contrast, the concentration decrease of the orbital- and charge-ordered states in is found to be a linear function of w. Valence mixing and charge ordering are therefore two separate cooperative phenomena. The enthalpy of the Verwey-type transition between these two cooperative systems is a linear function of w, which suggests that it originates from the latent heat of freezing into the long-range ordered orbital- and charge-ordered state. The enthalpy becomes zero at the nonstoichiometry level of about . [Copyright &y& Elsevier]

The nature of chemical bonds in a ferredoxin-type [2Fe–2S] cluster has been investigated on the basis of natural orbitals and several bond indices developed in Parts I and II of this study. The broken-symmetry hybrid density functional theory (BS-HDFT) with spin projection approach has been applied to elucidate the natural orbitals and occupation numbers for a model compound [Fe2S2(SCH3)4] (1), which is used to calculate the indices. The molecular structure, vibration frequencies, electronic structures, and magnetic properties in both oxidized and reduced forms of 1 have been calculated and compared with the experimental values. The optimized molecular structures after approximate spin projection have been in good agreement with experimental data. The structure changes upon one-electron reduction have been slight (<0.1 Å) and only limited around one side of the Fe atom. Raman and infrared (IR) spectra have been calculated, and their vibration modes have been assigned using the bridging 34S isotope substitution. Their magnetic properties have been examined in terms of spin Hamiltonians that contain exchange interactions and double exchange interactions. The BS-HDFT methods have provided the magnetic parameters; i.e., effective exchange integral (J) values and valence delocalization (B) values, which agree with the experimental results. It is found that large charge transfer (CT) from the bridging sulfur to the iron atoms has led to the strong antiferromagnetic interactions between iron atoms. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [ABSTRACT FROM AUTHOR]

Density-functional theory (DFT) calculations have been carried out for the radical anions 1,4-[Mes2B-(C6H4)-BMes2]·-(1) (Mes, mesityl), and for [B6Cl6]·-(2a), [B6Br6]·-(2b) and [B6I6]·-(2c). Previous EPR experiments had indicated significant spin delocalisation based on 1H, 10B and 11B hyperfine structure (1) and on g factor anisotropy (2a - c). Starting from optimized geometries the calculations confirmed this notion and yielded quantitative information on the spin distribution. While 1 with about 1/3 of spin density on each of the B atoms and on the organic bridge can be well-formulated as a delocalised (Class III) diboron(III,II) mixed-valent species with a p-phenylene spacer, similarly as the p-phenylenediamine radical cations, the paramagnetic anions 2 are trigonally Jahn-Teller distorted octahedral clusters with variable contributions from the halide substituents to the accommodation of the unpaired electron. While the chloride substituents in 2a participate rather little at the spin distribution, the iodide 2c is calculated with about equal contributions of 8% from individual B and I atoms to the singly occupied MO (SOMO). [ABSTRACT FROM AUTHOR]

A linear, trinuclear mixed valence complex [CoII{(μ-L)(μ-OAc)CoIII(NCS)}2] has been prepared and its molecular structure has been elucidated on the basis of X-ray crystallography [H2L=salen=1,6-bis(2-hydroxyphenyl)-2,5-diazahexa-1,5-diene]. The complex contains a high-spin CoII and two terminal low-spin CoIII, i.e., it is a CoIII(S =0)—CoII(S =3/2)—Co III(S =0) trimer. [Copyright &y& Elsevier]

The valence states and thermoelectric properties of two Ru-based uranium ternaries, namely U2Ru2Sn and U2RuGag, have been studied. Intermediate-valence behaviour manifests itself in broad peaks in the susceptibility, largely negative values of the paramagnetic Curie temperature, and in the occurrence of maxima in the thermoelectric power. At the same time, specific heat data show no transition at low temperatures for both studied compounds. Experimental results are fitted to equations given in the literature relevant to valence fluctuating states. The studied compounds are unique examples of such a state, found for the first time among the huge family of uranium compounds known to be magnetically ordered at low temperatures. [ABSTRACT FROM AUTHOR]

Accurate ab initio density-functional calculations are performed to understand structural stability, electronic structure, and magnetic properties of the ACr3O8( A = H, Li, Na, K, Rb, Cs) series. The ground-state structures for the compounds with A = Li−Rb take the same KCr3O8-type atomic arrangement (space group C2/ m), whereas CsCr3O8adopts a modified atomic architecture (prototype; space group Pnma), in agreement with available experimental findings. The hypothetical compound HCr3O8is found to stabilize in an LiV3O8-type structure (space group P21/ m), with an unexpectedly large equilibrium volume. The electronic structures of the ACr3O8compounds are analyzed using density-of-states, charge-density, and electron-localization-function plots, and all are found to exhibit semiconducting (insulating at 0 K) properties with very narrow band gaps. The Cr atoms occur in two different valence states and all compounds (except NaCr3O8) are found to exhibit antiferromagnetic ordering of magnetic moments at 0 K. [ABSTRACT FROM AUTHOR]

Abstract: The homocalixarenes p-tert-butyltetrahydroxy[3.1.3.1]metacyclophane (H4L1) and p-tert-butylhexahydroxy[2.1.2.1.2.1]metacyclophane (H6L2) react with UCl4 to give new polyphenoxide uranium complexes which have been characterized by X-ray diffraction. In the mononuclear compound [Hpy][UCl2(L1)]·2.5py (2), the UV centre is bound to the four phenoxide groups and two chlorine atoms. Further inclusion of hydrogen bonded counter-ions and solvent molecules in the macrocycle cavity results in dimerization through weak interactions. The tetranuclear complex [U4Cl2O2(L2)2(H2O)(thf)]·3thf (3) is a mixed valence compound comprising two UIV and two UV centres bound to three or four phenoxide groups each and bridged by two μ3-oxo, two chlorine and two phenoxide groups. The localization of the UIV and UV ions is indicated by the differing bond lengths. The crystal structure of the uncomplexed macrocycle H6L2 ·5py (1) is also reported. [Copyright &y& Elsevier]

Abstract: Electrons, electron holes, or excitations in finite or infinite ‘multimer systems’ may be localized or delocalized. In the theory of Hush, localization depends on the ratio Δ/λ (Δ/2=coupling; λ =reorganization energy). The latter theory has been extended to the infinite system [S. Larsson, A. Klimkāns, Mol. Cryst. Liq. Cryst. 355 (2000) 217]. The metal/insulator transition often takes place abruptly as a function of Δ/λ. It is argued that localization in a system with un-filled bands cannot be determined on the basis of Mott–Hubbard U alone, but depends on the number of accessible valence states, reorganization energy λ and coupling Δ (=2t). In fact U =0 does not necessarily imply delocalization. The analysis here shows that there are many different situations for an insulator to metal transition. Charge transfer in doped NiO is characterized by Ni2+ −Ni3+ exchange while charge transfer in pure NiO is characterized by a disproportionation 2Ni2+ →Ni+ +Ni3+. In spite of the great differences between these two cases, U has been applied without discrimination to both. The relevant localization parameters appear to be Δ and λ in the first case, with only two oxidation states, and U, Δ and λ in the second case with three oxidation states. The analysis is extended to insulator-metal transitions, giant magnetic resistance (GMR) and high T c superconductivity (SC). λ and Δ can be determined quite accurately in quantum mechanical calculations involving only one and two monomers, respectively. [Copyright &y& Elsevier]

Abstract: In this review the interaction between metal centers in dinuclear complexes based on azole and azine containing bridging ligands is reviewed. The focus of the review is on the manner in which the interaction pathway can be manipulated by variations in the nature of both the direct bridging unit and the peripheral substituents. Ruthenium polypyridyl type complexes will form the basis of this overview with particular attention paid to the electrochemical and spectroelectrochemical investigation of mixed valence compounds. [Copyright &y& Elsevier]

Abstract: A new three-dimensional open framework structure of mixed valence ethylenediamine–vanadium phosphate [C2H10N2][(HVIVO3)(HVVO2)(PO4)] (1), has been synthesized under mild hydrothermal conditions and characterized by elemental analyses, IR, fluorescent spectrum, TG-DTA and single crystal X-ray diffraction. Compound 1 exhibits a novel three-dimensional (3D) vanadium phosphate anion framework composed of vanadium, phosphate, and oxygen atoms through covalent bonds, with the diprotonated ethylenediamine [NH3CH2CH2NH3]2+ cations residing in the channels along c-axis. The organic diprotonated ethylenediamine cations interact with the O atoms in the inorganic network through hydrogen bonds. The electrochemical behavior of 1 has also been studied in detail by cyclic voltammograms, which is very important for practical applications in electrode modification. Furthermore, the strong photoluminescence property of compound 1 is also measured at room temperature. [Copyright &y& Elsevier]

Abstract: The reaction of the cross-bridged cyclam ligand H2CBC with divalent ytterbium precursors, Yb[N(SiMe3)2]2[L]2 (L=THF or Et2O) or Yb(C5Me5)2(OEt2) afforded polymeric [Yb(CBC)] n (1), as the primary product. In addition, the Yb[N(SiMe3)2]2[L]2 reactions also afforded a small amount of an unusual mixed valence salt containing a trinuclear Yb(III) cluster cation featuring a triply bridging NH group and a mononuclear Yb(II) anion, {[Yb(CBC)]3[μ3-NH]}+ {Yb[N(SiMe3)2]3}− (2). A related cluster containing an iodide counterion, {[Yb(CBC)]3[μ3-NH]}+ I− (3), was also isolated in one case. The structures of salts 2 and 3 were determined by X-ray crystallography. Reaction of [Yb(CBC)] n with p-tolyldisulfide, (C6H4MeS)2, produced burgundy crystals of [Yb(CBC)(S-p-C6H4Me)] n (4). The 1H NMR spectra of 2 suggests that the trinuclear cation remains intact in THF-d8 solution. [Copyright &y& Elsevier]