Rearrangement of the {Mo6S8}cluster fragment to {Mo4S4} and a New {Mo6S6} Cluster Nucleus: Crystal Structure of K6[Mo4S4(CN)12]·10H2O and (18-Crown-6K)8[Mo6S6(CN)16]·17.5H2O

Two new compounds containing molybdenum thiocyanide cluster anions, K₆[Mo₄S₄(CN)₁₂]·10H₂O (1) and (18-crown-6K)₈[Mo₆S₆(CN)₁₆]·17.5H₂O (2), were synthesized and investigated by X-ray structure analysis. Crystal data: a=11.8430(17), b=11.8430(17), c=35.170(7) , V=4932.8(14) ³, space group I4₁/a, Z=4, d_calc=1.563 g/cm³ for 1; a=28.7513(5), b=18.4190(3), c=20.7586(4) , =118.5982(7)°, V=9651.9(3) ³, space group C2/m, Z=4, d_calc =1.563 g/cm³ for 2. The [Mo₄S₄(CN)₁₂]^6- cluster anion in 1 has an ordinary structure typical of cubane transition metal complexes. In the structure of the [Mo₆S₆(CN)₁₆]^8- anion of 2, two crystallographically independent molybdenum atoms form a Mo₆ metallocluster, represented as two edge-sharing tetrahedra.     

Synthesis, Crystal Structure Determination, and Physicochemical Study of the Nickel(II) Complex of 4-(Pyridyl-2)-1,2,4-triazole

A new trinuclear nickel(II) complex with 4-(pyridyl-2)-1,2,4-triazole (pytrz), [Ni₃(pytrz)₆(H₂O)₆](NO₃)₆, has been synthesized, and its crystal structure has been determined. The compound was studied by X-ray phase analysis (XRPA), magnetochemical measurements, and electronic and IR spectroscopy.     

Molecular Structure of Bis(trimethylsilyl) Hypophosphite HP(OSiMe3)2 by Gas-Phase Electron Diffraction and Quantum Chemistry

Geometric parameters and conformation of the bis(trimethylsilyl)hypophosphite molecule were determined by gas-phase electron diffraction and quantum-chemical calculations. The molecule has an asymmetric structure, including an asymmetric P(OSiMe₃)₂ group. The principal geometric parameters are as follows: (r _a; in parentheses are standard deviations): bond lengths: P-O 1.616 and 1.633(1), Si-O 1.670(1), Si-C 1.892(1), C-H 1.097(3) Å; bond angles: OPO 100.8(8), POSi 133.3, and 138.4(3)°; torsion angles about P-O bonds 120(2) and 41.(3)°; and torsion angles about Si-O bonds are 145 and −178(4)°.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 6, 2005, pp. 897–902.Original Russian Text Copyright © 2005 by Naumov, Oberhammer, Tafipol’skii.     

Effects of specific interactions on the anisotropy of crystal structure distortion of [Co(NH3)5NO2]Cl2 under hydrostatic pressure

Using some special experimental techniques for anisotropic refinement of the crystal structure of [Co(NH₃)₅NO₂]Cl₂ at high pressures gave results with an accuracy comparable to that obtained in normal conditions. The anisotropy of lattice compression under pressure is determined by specific interactions in crystals, in particular, by NH-Cl and NH-O hydrogen bonds. The anisotropy of compression at increased pressure is qualitatively distinct from that caused by lowered temperature for the same structure. This difference is also due to specific interactions (hydrogen bonds) in the structure. Institute of Solid State Chemistry, Siberian Branch, Russian Academy of Sciences (Novosibirsk). Novosibirsk State University. Marburg University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 433–447, May–June, 1998. This work was supported by A. Humboldt Foundation.     

Dispersion of the local parameters of quasilocalized low-frequency vibrational modes in a low-temperature glass: direct observation via single-molecule spectroscopy

Spectra of single tetra-tert-butylterrylene chromophore molecules embedded in an amorphous polyisobutylene matrix as microprobes were recorded. The individual temperature dependences of the spectral linewidths for the same single molecules (SMs) in a broad temperature interval (1.6 < T < 40 K) have been measured. This enabled us to separate the contributions of tunneling two-level systems and quasilocalized low-frequency vibrational modes (LFMs) to the observed linewidths. The analysis of the T dependences yields the values of LFM frequencies and SM-LFM coupling constants for the LFMs in the local environment of a given chromophore. Pronounced distributions of the observed parameters of LFMs were found. This result can be regarded as the first direct experimental proof of the localized nature of LFMs in glasses.     

Evolution of the optical properties and the electrical resistivity of CaMnO3 during the substitution of Mo for Mn ions

The reflectance, the optical density, and the optical conductivity spectra of CaMn_{1 ? x} Mo _x O₃ (x ≤ 0.07) polycrystals are studied over a wide spectral region. The substitution of Mo⁶⁺ ions for Mn⁴⁺ ions leads to a strong decrease in the first high-energy phonon band, which is related to vibrations in the MnO₆ octahedron. The appearance of band-type charge carriers is detected in CaMn_{1 ? x} Mo _x O₃ with x ≤ 0.04, and carrier localization is observed in CaMn_0.93Mo_0.07O₃. This localization increases at T < 160 K, i.e., during the transition from the paramagnetic to the antiferromagnetic state with orbital ordering and a monoclinic structure. The optical conductivity spectrum of CaMn_0.93Mo_0.07O₃ exhibits a strong shift of fundamental absorption bands, which is associated with a change in the band structure because of a decrease in the splitting of the 3d levels of Mn in the crystal field.     

Heterogeneous magnetic and electronic states in Ca1−xLaxMnO3−δ (x⩽0.12) single crystals with electron doping

The magnetic, transport, and optical properties of electron-doped Ca_1−xLa_xMnO_3−δ single crystals with x  ?0.12 were studied. The magnetic measurements show that in single crystals with x=0$x=0$ and 0.05 the G-type AFM phase with weak FM component is realized and in crystals with x=0.10$x=0.10$ and 0.12 the G- and C-type AFM phases coexist. The C-type magnetic structure arises at less concentration of La than in polycrystalline samples as a result of oxygen vacancies being additional source of electrons. Under magnetic transitions in the G- and C-type phases, resistivity and magnetoresistance of the doped single crystals have anomalies. Optical absorption in IR range indicates formation of a charge gap in crystals with x=0.10$x=0.10$ and 0.12 at appearance of the C-AFM and monoclinic phase with orbital/charge ordering. By comparing optical and transport properties, heterogeneous electronic state and its relation with heterogeneous magnetic state are shown.     

Spontaneous polarization in one-dimensional Pb(ZrTi)O3 nanowires

Formation of spontaneous polarization in one-dimensional (1D) structures is a key phenomenon that reveals collective behaviors in systems of reduced dimensions, but has remained unsolved for decades. Here we report ab initio studies on finite-temperature structural properties of infinite-length nanowires of Pb(Zr0.5Ti0.5)O3 solid solution. Whereas existing studies have ruled out the possibility of phase transition in 1D chains, our atomistic simulations demonstrate a different conclusion, characterized by the occurrence of a ferroelectric polarization and critical behaviors of dielectric and piezoelectric responses. The difference is accounted for by the use of depolarizing effects associated with finite thickness of wires. Our results suggest no fundamental constraint that limits the use of ferroelectric nanowires and nanotubes arising from the absence of spontaneous ordering.     

Comparative study of p‐amino benzhydrazide and m‐amino benzhydrazide by free radicals and free electron transfer

The bimolecular electron transfer from p‐amino benzhydrazide (PABH) and its meta‐derivative (m‐amino benzhydrazide (MABH)) to specific one‐electron oxidant results in the formation of anilino radical. In case of PABH, reaction with ^?OH radicals results in the synchronous formation of adduct as well as anilino radical. The interesting observation is that the yield of the anilino radical increases with increase in pH. The effect of substitution also has a significant effect on the formation of adduct. In case of MABH, significant yield of anilino radical gets form on reaction with ^?OH radical. The free radical electron transfer from PABH and MABH to parent radical cation of non‐polar solvent also results in the formation of anilino radical only suggesting that the radical cation of PABH and MABH has short life time. The above results were supported by quantum chemical calculations. Copyright © 2013 John Wiley & Sons, Ltd.     

Magnetorefractive effect in La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> in the infrared spectral range

The reflection and magnetic reflection spectra, magnetic resistance, electrical properties, and equatorial Kerr effect in La_0.7Ca_0.3MnO₃ crystals have been complexly investigated. The measurements have been performed in wide temperature and spectral ranges in magnetic fields up to 3.5 kOe. It has been found that magnetic reflection is a high-frequency response in the infrared spectral range to the colossal magnetore-sistance near the Curie temperature. Correlation between the field and temperature dependences of the magnetic reflection and colossal magnetoresistance has been revealed. The previously developed theory of the magnetorefractive effect for metallic systems makes it possible to explain the experimental data at the qualitative level. Both demerits of the theory of the magnetorefractive effect in application to the magnets and possible additional mechanisms responsible for the magnetic reflection are discussed.