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Two polynuclear, mixed-valence, sandwich dodecanuclear manganese clusters [MnII4MnIII4MnII4(μ4-O)2(μ3-O2CH)2(thme)4(MeCO2)10(H2O)4]·4H2O (1) and [MnII4MnIII4MnII4(μ4-O)2(μ3-O)2(thmp)4(MeCO2)10(H2O)4]·10H2O (2) are reported by the reaction of 1,1,1-tris(hydroxymethyl)ethane (H3thme) or 1,1,1-tris(hydroxymethyl)propane (H3thmp) with manganese(II) salts in methanol under reflux conditions. 1 and 2 were characterized by single-crystal X-ray diffraction, PXRD, cyclic voltammetry (CV), and variable temperature magnetic studies. 1 and 2 crystallize in the monoclinic (P21/n) and triclinic (P-1) systems, respectively, and each structure consists of a dodecanuclear mixed-valent sandwich core. Magnetic data confirmed that both complexes show dominant antiferromagnetic interactions between metal centers. The fascinating features of the non-covalent supramolecular contacts have been explored. The interplay of O⋯H interactions (i.e. O-H⋯O and C-H⋯O contacts) gives rise to the consolidation of discrete units of 1 and 2 into supramolecular architecture. Catecholase activity data show that the present clusters catalyze the oxidation of 3,5-DTBC to 3,5-DTBQ with efficient Kcat values. [ABSTRACT FROM AUTHOR]

We report the synthesis of a Co(III) complex with the five-coordinate salen-type ligand (N,N′-bis(3,5-di-tert-butyl-2-hydroxybenzyliden)-1,7-diamino-4-methyl-4-azaheptane). This complex is stable in air with a trigonal bipyramidal geometry and we show spectroscopically and computationally that a high-spin triplet ground state is preferred. This spin state is readily modulated by introduction of an exogenous ligand (pyridine, acetonitrile) to yield a six-coordinate complex with low-spin ground state. The five-coordinate complex exhibits solvent- and ligand-dependent electrochemical behavior in solution for the CoII/IIItransition and undergoes a one-electron ligand oxidation to generate a phenoxyl radical species that is relatively stable in the absence of oxygen. We show that this phenoxyl radical species is a Class I mixed-valence compound that can undergo photoinduced inner-sphere charge transfer with the neighboring phenoxide. This process is mediated by the Co(III) center which acts as a bridge. Understanding this behavior will lead to a better understanding of a dicobalt bis-salen analog previously reported by our group as a proton reduction catalyst. [ABSTRACT FROM AUTHOR]

The reduction of CoIIIin the tetraamine-encapsulating ligand complex [CoIII{(μ-ET)(Me2)cyclen}(H2O)2]3+by [FeII(CN)6]4−has been studied kinetico-mechanistically at different pH, temperatures, and pressures. The process agrees with the expected outer-sphere redox mechanism, with the value of the encounter-complex equilibrium constant large enough to allow for kinetic determination of the first-order electron transfer reaction rate constant. The value of the encounter-complex equilibrium constant,Kpre-eq, is not only dependent on the charge of the redox partners, but also on the establishment of an important network of hydrogen bonds. These can also explain the differences obtained in the activation volumes determined for the diaqua andbis-hydroxo complexes. Neither the leaching of CoIInor the presence of [FeIII(CN)6]3−is observed in the final reaction medium, which indicates that a fast sequence involving substitution on the transient CoIIcomplex followed by a fast inner-sphere electron transfer takes place. This sort of mechanism has already been established for encapsulating pentaamine ligand complexes, but this is the first example of such a sequential reaction occurring on a tetradentate ligand complex. Preliminary UV–Vis and electrochemical characterization experiments have been conducted on the final reaction mixtures, suggesting the formation of a stable cyanide-bridged CoIII/FeIImixed-valence complex of the same type reported in the literature for encapsulating {CoIII(N)5} skeletons. The kinetics of formation of a new cyanido-bridged mixed-valence CoIII/FeIIcomplex has been studied at different temperatures and pressures. [ABSTRACT FROM AUTHOR]

Reaction of Na12[α-P2W15O56] · 18H2O with Mn(CH3COO)2 · 4H2O in the presence of K2S2O8 in acidic aqueous solution leads to isolation of a { } cluster-containing sandwich-type compound: αββα-K3Na11{ (H2O)2(P2W15O56)2} · 40H2O (1). Single-crystal X-ray diffraction analysis revealed that 1 shows the well-known Weakley-type sandwich-type structure consisting of two trivacant [α-P2W15O56]12− Dawson moieties linked by a central symmetric rhomb-like mixed-valence manganese cluster via W–O–Mn and P–O–Mn connections. Mixed-valence Mn-cluster-substituted sandwich-type complexes based on trivacant Dawson units are rarely observed in polyoxometalate chemistry. Further, the sandwich-type polyoxoanions were connected by [K3Na2] clusters into a 44-layer. Magnetic study indicates that antiferromagnetic interactions exist in this compound. [ABSTRACT FROM AUTHOR]

Two 2-D layered mixed-valence vanadium materials, [H2N(CH2)4NH2]4[VIVOPO4VVO(OH)PO4]4 (1) and [H2N(CH2)4NH2]2[V8O20] (2), have been synthesized under hydrothermal conditions and characterized by infrared spectroscopy, SEM, fluorescence spectroscopy, and single-crystal X-ray diffraction. The layer structure of 1 is composed of VIVO6 octahedra, PO4 tetrahedra, and VVO5 tetragonal pyramids sharing corners. Compound 2 has a 2-D framework constructed from [VO5] square pyramids sharing edges and corners. Adjacent [VO5] layers are connected through the rings to generate a spiral-like inorganic framework with eight-membered ring channels. SEM shows morphology of 1 and 2. Compounds 1 and 2 show intra-ligand fluorescence emission. [ABSTRACT FROM AUTHOR]

The binuclear complexes, trans-(isn)(NH3)4RuNCFe [image omitted] (n = 2-, 1-, 0), were prepared both in aqueous solutions and as isolated salts. Their properties, particularly that of the mixed-valence species (M), were characterized by UV-Vis, infrared, electrochemical and kinetic studies. The results suggested that Ru(III)-Fe(II) was both thermodynamically and kinetically stable oxidation states. The extent of delocalization of M was estimated by analysis of the intervalence band on the basis of Hush's theory. The stabilization of M with respect to its oxidation state isomer (M') was investigated and it was found that the electrostatic effect associated with the net charges of metal moieties constituted the dominant factor governing the stability of M. [ABSTRACT FROM AUTHOR]

Abstract: Lipid-packaged, mixed-valence linear platinum complexes are dispersed in chloroform, chlorocyclohexane and in methylcyclohexane. They show indigo-colors, which are identical to solid samples. These lipid-complexes display supramolecular thermochromism, resulting from heat-induced dissociation and recovery of coordination chains. Unexpectedly, reassembled samples show altered CT absorption spectra. In chloroform, the reassembled complex gives indigo-color, while the chlorocyclohexane and methylcyclohexane dispersions show blue and red-colors, respectively. These color changes indicate enhanced solvation of lipid-packaged platinum complexes after the heat treatment. The thermal re-assembly also affects the aggregate morphology, and leads to the formation of nanowires, nanofibers and nanoparticles depending on the solvents employed. The conversion of pseudo one-dimensional (1D) inorganic complexes to lipophilic supramolecular assemblies thus gives solvatochromic properties, which are elements not existing in the conventional solid-state inorganic chemistry. [Copyright &y& Elsevier]

Abstract: In this manuscript we review the structure of the novel 1-D chain complex, {[PtRh(PVM)2(NH3)2Cl2.5]2[Pt2(PVM)2(NH3)4]2(PF6)6·2MeOH·2H2O} n (4) (PVM=pivalamidate), consisting of mixed-valence dimeric complexes with appreciably extended metal–metal bondings. Compound 4 is made up of octameric segments, each of which consists of two platinum-rhodium dinuclear complexes and a tetrameric platinum unit. The charge of 19+ for the Pt6Rh2 octameric segment in 4 was deduced from the number of the independent PF6 − counter ions, and is the supporting evidence for one unpaired electron per one octameric segment. The tetrameric platinum unit in 4 is the structural motif that is observed in [Pt2(PVM)2(NH3)4](PF6)2·H2O (2) and [Pt4(PVM)4(NH3)8](PF6)4(ClO4)·2H2O (3=“platinum blue” with one electron delocalized over the four platinum atoms). On the basis of the EPR, magnetic susceptibility, and electrical conductivity results, the nature of the unpaired electron in 4 is discussed. [Copyright &y& Elsevier]

Two cyano-bridged copper(II)–copper(I) mixed-valence assemblies, Cu(EAM) 2 [Cu(CN) 2 ] 2 1 (EAM  =  ethanolamine) and Cu(DETA)[Cu(CN) 2 ] 2 ·0.5H 2 O 2 (DETA  =  diethylenetriamine), have been prepared and structurally and magnetically characterized. IR spectra indicate the presence of bridging cyano groups in both 1 and 2, confirmed by structure analyses; Cu(I)–CN–Cu(II), Cu(I)–CN–Cu(I) and Cu(I)–Cu(I) metal bond linkages are evident. In the lattice, a 3D network is formed by two [Cu(CN) 2 ]   - units and one [Cu(EAM) 2 ] 2+ unit for 1. Variable temperature magnetic susceptibilities, measured in the 5–300  K range, indicate weak antiferromagnetic exchange interactions in complex 1. [ABSTRACT FROM AUTHOR]

The dinuclear complex cis , cis -[(bpy) 2 ClRu(μ-bim)RuCl(bpy) 2 ] n + (bpy = 2,2′-bipyridine; bim = benzimidazolate; n = 1, 2, or 3) was synthesized, isolated as a hexafluorophosphate salt, and investigated in organic solutions by cyclic voltammetry and UV/visible/NIR spectroelectrochemistry. The mixed-valent species ( n = 2) displays significant metal-metal electronic coupling in the ground state but exhibits localized Ru(III) and Ru(II) oxidation states, as deduced from its intervalence charge transfer (IVCT) band and redox parameters. On the basis of the resonance energy ( H AB ) estimated in the context of Hush's semiclassical theory, the extent of intermetallic communication was found to be larger than that recently reported for the bta-bridged analog (bta = benzotriazolate). Some differences between the IVCT features of these systems have been rationalized in terms of the degree of σ,π-basic character of the bridging ligands, according to an electron superexchange mechanism of the "hole-transfer" type. The stabilization of the mixed-valent complexes is attributed mainly to cooperative metal-to-ligand/ligand-to-metal charge-transfer effects. The combined π-acceptor and σ,π-donor abilities of the ancillary (bpy) and bridging (bim or bta) ligands, respectively, are also responsible for the high stability of the fully oxidized (Ru III -L-Ru III ) and fully reduced (Ru II -L-Ru II ) isovalent species. [ABSTRACT FROM AUTHOR]