Mixed-valence Structure Research Articles

Valence structure and magnetic interaction in MMX-type 1D complexes, A 4[Pt 2I(P 2O 5H 2) 4]· nH 2O, studied by 31P solid NMR

31P MAS-NMR spectra and spin-lattice relaxation time T 1 in solid were measured on A 4 [Pt 2 I(P 2 O 5 H 2 ) 4 ].nH 2 O (A: Cs, Rb, K, Na and Li). Continuous spectrum changes in both line and splitting widths were observed with changing the cation size and the number of crystalline water. Complexes with A: Cs (n=0) and Rb (n=2) afforded two kinds of 31 P resonance lines with chemical shifts close to those in the Pt 3+ and Pt 2+ monomer complexes indicating a mixed valence structure. On the other hand, complexes with A: Na (n=2) and Li (n=4) yielded a broad single line suggesting the formation of paramagnetic Pt sites with an averaged valence of Pt 2.5+ . An analogous continuous change was observed in 31 P T 1 in consistent with the above analysis. The observed spectra and T 1 depending on the cation size and the H 2 O number suggest valence fluctuation due to spin jumps in and between Pt-Pt units sensitively influenced by crystal packings and hydrogen bonding.

Crystal Chemical Aspects of Vanadium: Polyhedral Geometries, Characteristic Bond Valences, and Polymerization of (VOn) Polyhedra

The distribution of bond lengths in (V3+O6) polyhedra shows a maximum between 1.98 and 2.04 Å, and limits of 1.88 and 2.16 Å, respectively. The bond lengths in (V4+On) and (V5+On) (n = 5, 6) polyhedra show distinct populations which allow us to define the following types of bonds: (1a) vanadyl bonds in (V4+On) polyhedra, shorter than 1.74 Å; (1b) vanadyl bonds in (V5+O5) polyhedra, shorter than 1.76 Å; (1c) vanadyl bonds in (V5+O6) polyhedra, shorter than 1.74 Å; (2a) equatorial bonds in (V4+On) polyhedra, in the range 1.90 to 2.12 Å; (2b) equatorial bonds in (V5+O5) polyhedra, longer than 1.76 Å; (2c) equatorial bonds in (V5+O6) polyhedra with one vanadyl bond, in the range 1.74 to 2.10 Å; (2d) equatorial bonds in (V5+O6) polyhedra with two vanadyl bonds, in the range 1.80 to 2.00 Å; (3a) trans bonds in (V4+O6) polyhedra, longer than 2.10 Å; (3b) trans bonds in (V5+O6) polyhedra with one vanadyl bond, longer than 2.15 Å; (3c) trans bonds in (V5+O6) polyhedra with two vanadyl bonds, longer than 2.025 Å. The average equatorial bond length in (V4+On) and (V5+On) polyhedra can be used to calculate the mean valence state of V in mixed-valent structures. We define characteristic bond valences for vanadyl, equatorial, and trans bonds in different coordinations and examine which binary linkages are possible and which linkages occur in minerals and synthetic compounds. Here, V5+−O−V5+, V5+−O−V4+, and V4+−O−V4+ linkages between vanadyl−trans and equatorial−equatorial bonds occur often in synthetic compounds, whereas the corresponding V4+−O−V4+ linkages are rare in minerals.

The Mixed Valence Structure of “R-NiF3”

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The Mixed Valence Structure of “R–NiF3”

XAS at the nickel K-edge and UV-visible studies of rhombohedral nickel trifluoride indicate that the compound has a mixed valence composition Ni[NiF6] and is isostructural with Pd[PdF6]. XAS data are reported for NiF2, [NiF6]2–, [NiF6]3–, Pd[PdF6], CoF3 and RhF3 in support of the Ni[NiF6] study. New data from refinements of X-ray powder diffraction of CoF3 and IrF3 are reported in the context of the distortion from hexagonal close packing of rhombohedral trifluorides. Die Struktur von gemischt-valentem „R–NiF3” Rontgen-Absorptionsspektren (XAS) an der Nickelkante und UV-Vis-Untersuchungen an rhomboedrischem Nickeltrifluorid zeigen, das diese Verbindung, Ni[NiF6], eine gemischt-valente Zusammensetzung hat und isostrukturell mit Pd[PdF6] ist. XAS-Daten von NiF2, [NiF6]2–, [NiF6]3–, Pd[PdF6], CoF3 und RhF3 werden zur Bestatigung der Untersuchung an Ni[NiF6] mitgeteilt. Neue Daten der Verfeinerung von Rontgen-Pulverdiffraktogrammen von CoF3 und IrF3 werden im Zusammenhang mit der Verzerrung der hexagonal-dichtesten Packung der rhomboedrischen Trifluoride mitgeteilt.

Supramolecular Soft−Soft Interactions of Diiodo(tert-butyl)(isopropyl)phosphonium Cations with μ2- to μ5-Bridging Iodide Anions. Formation of Chains, Helices, and Columnar Structures

tert-Butyl(isopropyl)iodophosphane (1) reacts with 1 equiv of iodine in dichloromethane furnishing yellow tert-butyl(isopropyl)diiodophosphonium iodide t-Bu(i-Pr)PI3 (2). A byproduct is red crystalline t-Bu(i-Pr)PI3.25 (3). Stepwise addition of iodine to 1 provides 2 and the tert-butyl(isopropyl)diiodophosphonium iodide/triiodides t-Bu(i-Pr)PI4 (4) and t-Bu(i-Pr)PI4.33 (5). NMR spectra from solutions prepared by adding various amounts of iodine to 1 always show only one 31P-NMR signal and one set of 1H-NMR resonances; chemical shifts and coupling constants, which depend on the amount of iodine added to 1, indicate rapid exchange equilibria in solution and decreasing cation−anion interactions with increasing iodine content. The solid state structures of 2−5 were determined by X-ray crystallography. 2 (orthorhombic, space group Pbcn, Z = 8, a = 13.413(3) Å, b = 14.693(3) Å, c = 14.240(3) Å) consists of helical chains of tert-butyl(isopropyl)diiodophosphonium ions bridged by μ2-iodide anions through iodine−iodine interactions. t-Bu(i-Pr)PI3.25 (3) (tetragonal, space group P4/ncc, Z = 16, a = 19.730(3) Å, c = 14.485(4) Å) is [t-Bu(i-Pr)PI2]4(μ2-I)2(μ4-I)[I(I2)x] (mixed-valence columnar structure, x ≈ 0.5): 16-membered rings from four t-Bu(i-Pr)PI2−I moieties are connected in a spiro fashion by μ4-iodide anions; each channel between four of these cationic stacks is occupied by iodine ([I(I2)x]-, disordered). The backbone of the chain structure of crystalline 4 (orthorhombic, space group P212121, Z = 4, a = 9.462(2) Å, b = 11.130(3) Å, c = 30.228(6) Å) is formed by [−P−I−I−I−] units from tert-butyl(isopropyl)diiodophosphonium ions and μ3-donor iodide ions, each of which is connected with one iodine atom of a further side chain tert-butyl(isopropyl)diiodophosphonium ion. The other iodine atom of this side chain cation is coordinated by a terminal triiodide ion. 5 (monoclinic, space group P21/c, Z = 4, a = 23.874(9) Å, b = 21.858(7) Å, c = 9.477(3) Å, β = 94.30(3)°) contains a double chain backbone of μ2-acceptor phosphonium ions and μ5-bridging donor iodide ions. Four I···I contacts of these μ5-bridging donor iodide ions are within the double chain, and the fifth is to a side chain tert-butyl(isopropyl)diiodophosphonium ion, which is also connected to a terminal triiodide anion by an I···I interaction. A further triiodide anion within the unit cell has no soft−soft interaction with the cationic network.

Mixed-valence states and crystal structure of biferrocene derivatives with long alkyl chains

Mixed-valence states have been investigated for a series of binuclear ferrocenium salts with long alkyl chains. In the triiodide salts with layered structures, an interesting even-odd character in the number of carbon atoms of the alkyl chain is observed in the relationship between the inter-layer distance and the mixed-valence state. 1′, 1‴-didodecylbiferrocenium triiodide is found to be most interesting because this salt has a large potential for application to molecular-based devices.

ChemInform Abstract: Syntheses and Chemical Properties of Platinum Blues

Since the first report in 1908, a class of platinum compounds called “platinum blues” have attracted interests of chemists because of their unusual dark blue color. However, because of the difficulty in isolating and crystallizing the complexes, their formulas and structures have been left unclarified till a decade ago. About ten years ago when it turned out that the famous anti-tumor complex cis-Pt (NH3) 2CL2 effects its activity by binding to DNA and obstructing the DNA duplication, a study regarding the coordination reaction of cis-Pt (NH3) 2Cl2 with pyrimidine bases started and the platinum pyrimidine blues found in the study again aroused interest of chemists. In the course of intensive studies, the first crystal structure determination of platinum blue was carried out for a compound with α-pyridone as a pyrimidine model and the tetranuclear 5+ mixed-valent chain structure of [Pt4 (NH3) 8 (C5H4NO) 4] was revealed.In the present article, syntheses, structures and chemical properties of platinum blues and several other related multinuclear platinum complexes containing hetero metal atoms are surveyed with an emphasis on the specific nature of amidate ligands that stabilize unusually high oxidation state of metals.

白金ブルー錯体の合成とその性質

Since the first report in 1908, a class of platinum compounds called “platinum blues” have attracted interests of chemists because of their unusual dark blue color. However, because of the difficulty in isolating and crystallizing the complexes, their formulas and structures have been left unclarified till a decade ago. About ten years ago when it turned out that the famous anti-tumor complex cis-Pt (NH3) 2CL2 effects its activity by binding to DNA and obstructing the DNA duplication, a study regarding the coordination reaction of cis-Pt (NH3) 2Cl2 with pyrimidine bases started and the platinum pyrimidine blues found in the study again aroused interest of chemists. In the course of intensive studies, the first crystal structure determination of platinum blue was carried out for a compound with α-pyridone as a pyrimidine model and the tetranuclear 5+ mixed-valent chain structure of [Pt4 (NH3) 8 (C5H4NO) 4] was revealed.In the present article, syntheses, structures and chemical properties of platinum blues and several other related multinuclear platinum complexes containing hetero metal atoms are surveyed with an emphasis on the specific nature of amidate ligands that stabilize unusually high oxidation state of metals.

Supramolecular phenomena in organic redox films at electrodes: Part I. The methylene blue/leucomethylene blue redox couple at the platinum electrode

It is possible to generate conductive multilayer structures by reduction of methylene blue cations at the interface: clean surface of a platinum electrode/1 M aqueous electrolyte solution. The characteristics of the multilayer ordered phase generated in fluoride and nitrate solutions are presented and the mechanism of a fast charge transfer between electrode/organic film and organic film/aqueous solution interfaces is discussed. The conductivity of the film is interpreted by postulating formation of a mixed valence structure with the generation of a cation radical intermediate which is favoured in the solid state at characteristic potentials.

P4W8O32: a mixed-valence tunnel structure built up of ReO3-type slabs connected through PO4 tetrahedra

P4W8O32: a mixed-valence tunnel structure built up of ReO3-type slabs connected through PO4 tetrahedra

Mössbauer study of Co and Fe spinels acting as sources and absorbents

Mössbauer spectra and X-ray powder diagrams of synthetic 57Co and 57Fe oxides having the two lattice-site spinel structure have been obtained. The distribution of iron and cobalt atoms between the octahedral and tetrahedral lattice sites has been determined by means of isomer shift and quadrupole splitting measurements. A new mechanism is proposed in order to explain the distribution of 57Fe as well as its charge state when it enters the lattice as an impurity. At high temperature a mixed valence structure of Co 3O 4 was found. It is argued that the charge state of the daughter iron depends on the vacancy concentration in the environment of those sites where the corresponding decay takes place. Single line sources are obtained under well determined conditions.

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A novel mixed valence tellurium oxide, TiGa0.67Te2.33O8, was synthesized and its crystal structure determined using the X-ray powder diffraction technique. The obtained oxide was found to crystallize in a cubic unit-cell, Ia3¯ space group, with the lattice parameter a = 10.9557(1) Å. Rietveld refinement of the structure led to ultimate confidence factors Rp = 7.63 and Rwp = 6.71. This structure was based on slabs containing groups of (Te/Ga)O4 joined by the metal cations Ti4+. The structure analysis showed a cation ordering of Te4+ and Te6+ yielding a TiGa2/3Te7/3O8 formula. The IR and RAMAN spectra confirmed the presence of the TiO6 and (Te/Ga)O4 groups. The dielectric anomalies observed at 500 K were attributed to the mixed valence structure, arising from the mixed-valence Te6+/Te4+. We detected only one peak in thermal behavior by the DTA/TG analysis; which implied a melting reaction.