Unligated diruthenium(II,II) tetra(trifluoroacetate): the first X-ray structural study, thermal compressibility, Lewis acidity, and magnetism

The title compound, [Ru(2)(O(2)CCF(3))(4)] (1), has been obtained without any exogenous ligands and crystallized by deposition from the gas phase at 170 degrees C. Its crystal structure has been determined for the first time to confirm an infinite chain motif built on axial Ru...O interactions of the diruthenium(II,II) units. The X-ray diffraction studies at variable temperatures showed no phase transitions in the range of 295-100 K but revealed a significant decrease in the volume per atom from 14.2 to 13.3 A(3). This noticeable thermal compressibility effect is discussed in connection with the solid-state packing of the [Ru(2)(O(2)CCF(3))(4)](infinity) chains. The highly electrophilic character of the diruthenium(II,II) units has been shown by the gas-phase deposition reaction of [Ru(2)(O(2)CCF(3))(4)] with an aromatic donor substrate, namely [2.2]paracyclophane (C(16)H(16)). As a result of the above reaction, a new arene adduct [Ru(2)(O(2)CCF(3))(4).C(16)H(16)] (2) has been isolated in crystalline form. It has an extended one-dimensional (1D) chain structure comprised of alternating building units and based on the rare bridging mode of [2.2]paracyclophane, [Ru(2)(O(2)CCF(3))(4).(mu(2)-eta(2):eta(2)-C(16)H(16))](infinity). The magnetic susceptibility of 1 and 2 has been measured and compared in the range of 1.8-300 K. In addition, in the course of synthesis of 1 by the carboxylate exchange reactions, a new mixed-carboxylate diruthenium(II,II) core complex [Ru(2)(O(2)CCF(3))(3)(O(2)CC(2)H(5))] (3), bearing no exogenous ligands, has also been isolated and structurally characterized. It exhibits an interesting polymeric structure in which the ruthenium(II) centers selectively form axial interdimer contacts with the O-atoms of the propionate groups only.     

Fluorinated heterometallic β-diketonates as volatile single-source precursors for the synthesis of low-valent mixed-metal fluorides

Hexafluoroacetylacetonates that contain lead and divalent first-row transition metals, PbM(hfac)(4) (M = Ni (1), Co (2), Mn (3), Fe (4), and Zn (5)), have been synthesized. Their heterometallic structures are held together by strong Lewis acid-base interactions between metal atoms and diketonate ligands acting in chelating-bridging fashion. Compounds 1-5 are highly volatile and decompose below 350 °C. Fluorinated heterometallic β-diketonates have been used for the first time as volatile single-source precursors for the preparation of mixed-metal fluorides. Complex fluorides of composition Pb(2)MF(6) have been obtained by decomposition of 1-5 in a two-zone furnace under low-pressure nitrogen flow. Lead-transition metal fluorides conform to orthorhombically distorted Aurivillius-type structure with layers of corner-sharing [MF(6)] octahedra separated by α-PbO-type (Pb(2)F(2)) blocks. Pb(2)NiF(6) and Pb(2)CoF(6) were found to exhibit magnetic ordering below 80 and 43 K, respectively. The ordering is antiferromagnetic, with a weak, uncompensated moment due to the canting of spins. The Pb(2)MF(6) fluorides represent a new class of prospective magnetoelectric materials combining transition metals and lone-pair main-group cations.     

Thermally stimulated currents for a mixed free-carrier recombination mechanism

Analytical expressions are obtained in this paper for thermally stimulated currents in the ordinary and photoelectret modes for a mixed mechanism of free-charge-carrier recombination and a strong duplicate attachment. It is shown that in this case the same trap parameters can be determined from experimental curves for thermally stimulated currents as for bi- and monomolecular recombination; however, the majority of computation methods should be modified. Modified formulas are proposed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 92–97, July, 1976.The authors are grateful to A. R. Regel' for interest in the research and for useful consultation, and also to B. S. Medved' for aid in computing the curves on an electronic computer.     

Absolute Logarithmic Norm

In this paper we introduce and study a new concept of the absolute logarithmic norm, which has much in common with the classical definition of the logarithmic norm by S. M. Lozinskii. The the theory that we develop allows to obtain new facts from the Lyapunov stability theory for the systems of linear differential equations with constant coefficients. The presentation of the material relies heavily on the theory of off-diagonally nonnegative matrices arising from the Perron–Frobenius theory for nonnegative matrices.     

Synthesis,structure, and properties of LnBiI<Subscript>6</Subscript>•13H<Subscript>2</Subscript>O (Ln = La,Nd)

Two new iodobismuthates with the composition LnBiI₆?13H₂O (Ln = La, Nd) were synthesized and their crystal structures were determined. The compound LaBiI₆?13H₂O crystalizes in the orthorhombic space group Pna2₁, a = 24.206(5), b = 8.405(1), c = 26.360(5) Å; the compound NdBiI₆?13H₂O crystalizes in the monoclinic space group P2₁/n, a = 14.553(3), b = 13.386(3), c = 27.541(6) Å, β = 92.80(3)°. In both crystal structures, the cations Ln(H₂O)₉³⁺ and the anions BiI₆^3– alternate, forming a NaCl-type structure, and the structures themselves differ in the arrangement of water of crystallization that leads to the formation of dissimilar systems of hydrogen bonds. Both compounds undergo decomposition when heated, which is accompanied first by a partial liberation of water molecule, followed by pyrohydrolysis to form oxoiodides LnOI as final solid products. According to optical measurements, the band gap of the obtained compounds was equal to 1.78 (La) and 1.71 (Nd) eV.     

Homoleptic tetranuclear complexes of divalent tin and lead tetraolates

Homoleptic tetranuclear complexes of divalent tin and lead tetraolates, M(4)(hfpt)(2) [M = Sn (1) and Pb (2); hfpt(4-) is an anion of 1,1,1,5,5,5-hexafluoropentane-2,2,4,4-tetraol], have been obtained in high yield from the corresponding (trimethylsilyl)amides. The solid-state structures of 1 and 2 contain discrete molecules in which a butterfly tetrahedron of metal atoms is sandwiched between two tetraolate ligands acting in tetradentate mode. The lone-pair Sn(2+) and Pb(2+) cations exhibit pyramidal coordination of four ligand oxygen atoms. A multinuclear NMR study unambiguously confirmed that metal tetraolates retain their polynuclear structure in solution of even coordinating solvents. An interesting example of the strong through-space coupling between (19)F of the tetraolate trifluoromethyl groups and (117/119)Sn or (207)Pb nuclei was found. Both compounds were shown to have clean, low-temperature decomposition that results in crystalline oxides SnO(2) and PbO, respectively, for 1 and 2. This work demonstrates the remarkable coordination properties of the tetraolate ligand that can be utilized for the preparation of a wide variety of poly- and heterometallic complexes. Decomposition studies revealed a great potential of metal tetraolate complexes as prospective molecular precursors for the soft chemistry approach to oxide materials.     

Heterotrimetallic Mixed‐Valent Molecular Precursors Containing Periodic Table Neighbors: Assignment of Metal Positions and Oxidation States

A known trinuclear structure was used to design the heterobimetallic mixed‐valent, mixed‐ligand molecule [Co^II(hfac)₃?Na?Co^III(acac)₃] ( 1 ). This was used as a template structure to develop heterotrimetallic molecules [Co^II(hfac)₃?Na?Fe^III(acac)₃] ( 2 ) and [Ni^II(hfac)₃?Na?Co^III(acac)₃] ( 3 ) via isovalent site‐specific substitution at either of the cobalt positions. Diffraction methods, synchrotron resonant diffraction, and multiple‐wavelength anomalous diffraction were applied beyond simple structural investigation to provide an unambiguous assignment of the positions and oxidation states for the periodic table neighbors in the heterometallic assemblies. Molecules of 2 and 3 are true heterotrimetallic rather than a statistical mixture of two heterobimetallic counterparts. Trinuclear platform 1 exhibits flexibility in accommodating a variety of di‐ and trivalent metals, which can be further utilized in the design of molecular precursors for the NaMM′O₄ functional oxide materials.     

Pb2.63Cd2V3O12, a cation‐deficient garnet‐type vanadate

In the crystal structure of the cation‐deficient garnet Pb_2.63Cd₂V₃O₁₂ (lead cadmium vanadium oxide), the Cd and V atoms fully occupy octahedral and tetrahedral sites, respectively, whereas the Pb atoms partially occupy a dodecahedral site. The total Pb and Cd content indicates that vanadium is slightly reduced from the +5 oxidation state.