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Noble metal halide compounds are an exciting class of materials which display unique crystal chemistry with temperature and pressure. Here we report two new compounds, single-valence formamidinium platinum iodide [(FA) 2 Pt IV I 6 ] and mixed-valence methylammonium gold iodide [(MA) 2 Au I Au III I 6 ]. Structural changes between 300 K and 100 K have been monitored. The compounds crystallize in two different perovskite-related structure classes, with the added complexity of a disordered, “tumbling”, organic cation at 300 K. This tumbling is significantly reduced at 100 K. (FA) 2 Pt IV I 6 undergoes in-phase octahedral tilting similar to related vacancy-ordered perovskite materials. At 100 K, (MA) 2 Au I Au III I 6 undergoes a transition which facilitates stronger Au–I covalent bonding as made evident by a contraction of the unit cell and distances between Au and I atoms in the ab plane. [ABSTRACT FROM AUTHOR]

[Display omitted] • An unsymmetrical mixed-valence oxidovanadium(IV/V) binuclear complex was synthesized. • DFT calculations and EPR spectroscopy indicates a localized mixed-valence. • The bromoperoxidase activity using the phenol red was evaluated. The mixed-valence binuclear complex [{VO(acac)(bpy)}(μ–O){VO(bpy)(ox)}]·2H 2 O (1), where acac− = acetylacetonate, bpy = 2,2-bipyridine and ox2− = oxalate, was synthesized under mild conditions and characterized by elemental analysis and infrared (IR), electron paramagnetic resonance (EPR), and electronic (UV/Vis) spectroscopies. According to single-crystal X-ray diffraction data, the two nonequivalent oxidovanadium centers of the {(VO) 2 (μ-O)}3+ core adopt an anti -angular configuration and differ in the O , O -donor ligands. Density functional theory (DFT) at the ωB97X-D/def2TZVP level was used to optimize the molecular structure and describe the electronic structure of 1 in the solid state, indicating a localized mixed-valence system. Continuous-wave EPR analysis at 77 K suggests the predominance of binuclear species in dmf and dmso solutions of 1 and 1:1 mixtures of these solvents with water. This finding is supported by comparing experimental and calculated rotational radius, g-tensor and vanadium hyperfine couplings. In the presence of KBr and H 2 O 2 , complex 1 acts as a pre-catalyst in a solvent-modulated bromination of phenol red to produce bromophenol blue. Kinetic studies in dmf/H 2 O indicate a first-order dependence on vanadium with a reaction rate constant of 703 mol−2 L2 s−1. The better performance of 1 as a pre-catalyst in dmf/H 2 O than in dmso/H 2 O may be due to a higher formation rate for the active oxidoperoxidovanadium(V) species. [ABSTRACT FROM AUTHOR]

Highlights: [•] One mixed-valence CoIIICoII complex derived from a Robson type macrocyclic ligand. [•] Rare example of an active cobalt catalyst for catechol oxidase activity. [•] Single crystal X-ray structure and ESI-MS spectra. [•] Unique examples of hydrogen bonded metal complex⋯solvent aggregates in gas phase (ESI-MS). [•] Drastic change of properties as a result of slight change in ligand periphery. [ABSTRACT FROM AUTHOR]

Highlights: [•] First tri- and tetra-nuclear Mn complexes with a thiophene-(Th-)carboxylato ligand. [•] Mixed-valence trinuclear Mn compounds with {MnIIMnIII 2(μ-O)(O2CTh)6} core. [•] Homo-valence tetranuclear Mn complexes with {MnIII 4(μ-O)2(O2CAr)9} core. [•] Mixed-valence tetranuclear Mn complex with {MnIIMnIII 3(μ-O)2(O2CTh)7} core. [•] Antiferromagnetic interactions dominate within tetranuclear clusters. [Copyright &y& Elsevier]

Abstract: The electrochemical oxidation of a series of dicobalta–superphanes has been studied. Complexes in which the redox centers are connected by four propano-bridges display two one-electron oxidations, at least one of them being reversible, at potentials close to that of the ferrocene oxidation. The potential separation of the successive anodic processes is suggestive of strong transannular electronic interactions between the two redox sites. Two complexes (6 and 7) having one or both of their cyclopentadienyl caps substituted with a methyl ester, and containing two ethano-bridges and two 1,3-disilapropano-bridges, have been similarly studied and the IR spectra of their oxidation products recorded. The monocation 7 + displays two IR-active νCO bands, indicative of trapped valency, but both bands are shifted from the energies observed for the fully oxidized or reduced redox sites. Combined with the large ΔE 1/2 value for separation of the two one-electron oxidations of 7, the data are taken to denote a spin-localized but charge-delocalized model of the mixed valence state. Approximately 20% of the positive charge is transferred to the “unoxidized” side of the monocation 7 +. Electrochemical data are also presented on the reductions of cobalt and dicobalta–superphanes having cyclobutadienone moieties linked by propano-bridges. [Copyright &y& Elsevier]

Abstract: A homoleptic hexanuclear Cu cluster, [(Cu(DSB)(CBT))2(Cu2Br)2][PPh4]2 (1-PPh4 ) [DSB=2,3-disulfidobenzoate; CBT=3-carboxybenzene-1,2-bis(thiolate)] was synthesized as dark green crystals by the reaction of CuCl2 with 2,3-dimercaptobenzoic acid in acetate buffer solution. The X-ray crystal study of 1-PPh4 revealed its unique structural features: (1) one of two types of crystallographically distinct Cu centers adopted a square planer geometry and the other center had a tetrahedral geometry, and (2) intermolecular H-bonding interactions connected between carboxylic acid group of CBT and the carboxylate group of DSB led to the construction of an unprecedented topologic architecture of a zigzag patterned infinite sheet. In addition, taking into account the total charge of the molecule, which contained 2,3-disulfidobenzoate and 3-carboxybenzene-1,2-bis(thiolate), and the diamagnetic nature of 1-PPh4 , 1-PPh4 led to it is assignment as a mixed-valence Cu(I)/Cu(III) cluster. Such mixed valence states of Cu atoms were also examined by density functional theory calculation. [Copyright &y& Elsevier]

Abstract: Three complexes of composition [Co2 IICo2 III(H2hbhpd)2(H4hbhpd)2(H2O)2]Cl2(CH3OH)4 (1), [Co2 IICo2 III(H2hbhpd)2(H4hbhpd)2(H2O)2](NO3)2(CH3OH)4 (2) and [Ni2(H4hbhpd)2(NO3)](NO3)(CH3OH)1.5 (3) (H5hbhpd=2-(2-hydroxy-benzylamino)-2-hydroxymethyl-propane-1,3-diol) have been synthesized and their structures have been characterized. Complexes 1 and 2 are mixed-valence cobalt clusters and display face-sharing monovacant dicubane structures. In the complexes 1 and 2, one of the three alkyl hydroxyl groups of H5hbhpd ligand is deprotonated instead of deprotonation of phenyl hydroxyl group; thus monoanionic H4hbhpd− ligand displays novel η3, η1, η1, μ3 coordination mode. Complex 3 is binuclear, and the two metal centers of 3 are bridged by two deprotonated phenyl hydroxyl oxygen atoms and iso-orthogonalized by a nitrato group in η1η1-O,O′ coordination fashion. Variable-temperature solid-state dc magnetization studies have been performed in the temperature range 2–300K for compounds 1 and 3. Antiferromagnetic interactions were determined for 1 and ferromagnetic couplings were found for 3. [Copyright &y& Elsevier]

Abstract: The reaction of [(2-Pyridylmethylamino)carbonyl]ferrocene with Cu(ClO4)2 ·6H2O under conventional condition in the absence of base affords a monocopper compound, [Cu(Hpmaf)2(CH3OH)2](ClO4)2] 1, while that under solvothermal condition in the presence of triethylamine gives a dicopper compound, [Cu2(pmaf)2](ClO4) 2, (Hpmaf=[(2-Pyridylmethylamino)carbonyl]ferrocene). Both compounds were characterised by elemental analysis, IR and X-ray diffraction analysis. Compound 2 was further characterised by UV–vis and electron paramagnetic resonance (EPR), and the results indicate that it is a fully delocalised mixed-valence dicopper compound. This is the first example of mixed-valence dicopper compound containing ferrocene group. [Copyright &y& Elsevier]

Abstract: In this article I review the application of the group-theoretical approaches to a wide area of molecular magnetism dealing with metal clusters. The following main aspects are discussed: (1) irreducible tensor operator (ITO) approach that is based on the so-called “spin-symmetry”. Use of this approach in molecular magnetism has given a revolutionary impact on the evaluation of the energy levels, thermodynamic and spectroscopic properties of high-nuclearity metal clusters. ITO approach facilitated development and applications of the isotropic and anisotropic spin-Hamiltonians and the study of the magnetic anisotropy in clusters containing orbitally degenerate metal ions; (2) group-theoretical classification (assignment) of the exchange multiplets based on both spin-symmetry and point symmetry that allows to analyze the non-Heisenberg forms of the exchange interaction and magnetic anisotropy in general terms, establishes selection rules for magnetic resonance transitions and facilitates computation of spin levels. This approach allows also to reveal the selection rules for the active Jahn–Teller coupling and to clear understand the interrelation between spin frustration and structural instabilities; (3) group-theoretical classification of the delocalized electronic and electron-vibrational states of mixed-valence compounds in terms of spin and point symmetries (including delocalization of the electronic pair) that essentially reduces the time of calculations and provides direct assess to the selection rules for different kinds of transitions. This becomes crucial in the dynamical vibronic problems inherently related to mixed-valency even for the truncated basis sets when the calculations become hardly executable not only in the case of strong vibronic coupling but even provided that the vibronic coupling is moderate. The proposed approach includes the design of the symmetry adapted vibronic basis and can enormously extend computational abilities in the dynamical problem of mixed-valency. [Copyright &y& Elsevier]

Abstract: The series of complexes [Co(Q)2(bpy)] n (n =−1, 0, +1) that can be derived by partial reduction or oxidation of complex 1, ls-Co(III) has been synthesized and studied. The results support the theoretical calculations which pointed to an intervalence transfer (IT) from the Cat2− to the SQ− ligand rather than a LMCT transition as the origin for the low-energy band transition centered at 2500nm observed for 1, ls-Co(III). [Copyright &y& Elsevier]

Abstract: The complexes [{Ru(tpy∗)(bpy)}2(μ-adpc)][PF6]2 where tpy∗ is 4,4′,4″-tri-(tert-butyl)-2,2′:6′,2″-terpyridine, bpy is 2,2′-bipyridine, and adpc2− is 4,4′-azo-diphenylcyanamide dianion and trans,trans-[{Ru(tpy∗)(pc)}2(μ-adpc)] where pc− is 2-pyrazine-carboxylato were prepared and characterized by cyclic voltammetry and spectroelectrochemical methods. Intervalence band properties and IR spectroelectrochemistry of the mixed-valence complexes [{Ru(tpy∗)(bpy)}2(μ-adpc)]3+ and trans,trans-[{Ru(tpy∗)(pc)}2(μ-adpc)]+ are consistent with delocalized and valence-trapped mixed-valence properties respectively. The reduction in mixed-valence coupling upon substituting a bipyridine ligand with 2-pyrazine carboxylato strongly suggests that hole-transfer superexchange is the dominant mechanism for metal–metal coupling in these complexes. [Copyright &y& Elsevier]

One novel cyanide-bridged mixed-valence {FeIII 2 (μ -CN) 4 FeII 2 } square cluster exhibits thermally-induced, reversible, complete spin transition behaviour at two out of four metal centers. • One novel cyano-bridged mixed-valence bimetallic {FeIII 2 (μ -CN) 4 FeII 2 } cluster has been prepared. • The square cluster exhibits thermally-induced, reversible, complete spin transition behavior. One novel cyano-bridged mixed-valence bimetallic {FeIII 2 (μ -CN) 4 FeII 2 } cluster, {[(Tp)FeIII(CN) 3 ] 2 [FeII(Py 2 N 2)] 2 }·(PF 6) 2 (1), has been synthesized (Tp = hydrotris(pyrazolyl)borate, Py 2 N 2 = N,N'-bis(2-pyridylmethyl)-N,N'-bis(4-benzyl)-1,2-ethanediamine). The molecular structure has been determined by single-crystal X-ray diffraction. Compound 1 exhibit temperature driven Fe(II) spin crossover behaviour (SCO) associated with the high-spin (HS) ↔ low-spin (LS) transition with the transition temperature of 130 K at two out of four metal centers. The evolution of HS and LS Fe(II) ions with temperature was followed by FT-IR, X-ray crystallography, the variable temperature magnetic susceptibility. [ABSTRACT FROM AUTHOR]