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Boris Zemva

Publications and source records attributed to Boris Zemva.

12 recordsLinked to original sources
PubMed2006

Anomalously large formula unit volume and its effect on the thermal behavior of LiBF4.

The crystal structure of LiBF4 has been determined by single-crystal X-ray diffraction measurements. LiBF4 crystallizes as a merohedral twin in the trigonal space group P3(1)21 with a=4.892(5) A, c=11.002(12) A, V=228.0(4) A3, and Z=3 at 200 K. The twin is generated by a 2-fold rotation about the [10] direction. The lithium cation is coordinated by four fluorine atoms in a distorted tetrahedral manner, wherein two Li-F distances of 1.862(5) and 1.846(5) A are observed. The formula unit volume (FUV=V/Z) of 77.9 A3 for LiBF4 at 298 K is considerably larger than 72.7 A3 for NaBF4 and 72.5 A3 for AgBF4, despite the smaller size of Li+, indicating loose ionic packing of LiBF4. The thermodynamic evaluation of the decomposition temperature for LiBF4 was performed using the empirical relationship between the standard entropy and the FUV obtained. The results indicate that the large FUV of LiBF4 contributes to its higher decomposition temperature compared to that of LiPF6.

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PubMed2006

Coordination of XeF2 to calcium and cadmium hexafluorophosphates(V).

[M(XeF2)5](PF6)2 (M = Ca, Cd) complexes were prepared by the reaction of MF2 and XeF2 under pressure of gaseous PF5 in anhydrous HF as solvent. The coordination sphere of the Ca atom consists of nine fluorine atoms: three from two PF6(-) units (one bidentate and one monodentate) and one from each of six XeF2 molecules. The coordination sphere of the Cd atom consists of eight fluorine atoms: one from each of two PF6(-) units and one from each of six XeF2 molecules. Two of the XeF2 ligands about M in each compound are bridging ligands and are each linked to two M, generating infinite (-M-F-Xe-F-M-F-Xe-F-) chains along the b-axis in the Ca salt and along the c-axis in the Cd compound. The Cd2+ cation is smaller and more electronegative than the Ca2+ cation. These differences account for the higher F ligand coordination in the Ca2+ salt and for other structural features that distinguish them. The different stoichiometry of the PF6(-) salts when compared with their AsF6(-) analogues, which have the composition [M(XeF2)4](AsF6)2 (M = Ca, Cd), is in accord with the lower F ligand charge in the AsF6(-) when compared with that in the PF6(-) compound. Indeed, the AsF6(-) ligand charges appear to be similar to those in the XeF2-bridged species.

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PubMed2005

XeF2 as a ligand in a coordination compound with the BF4- anion.

The first tetrafluoroborate compound with XeF2 coordinated to a metal center, [Cd(XeF2)](BF4)2, has been synthesized. It crystallizes in monoclinic space group P21/a with a = 8.785(11) A, b = 9.079(2) A, c = 10.718(6) A, beta = 110.824(6), and Z = 4. Its crystal structure and that of Cd(BF4)2 have been solved. The latter crystallizes in orthorhombic space group Pbca. Both syntheses were performed in aHF as solvent, at room temperature, yielding colorless solids. The Raman spectra of the solids are in harmony with the crystallographic findings. [Cd(XeF2)](BF4)2 has been shown to be in equilibrium with XeF2 and Cd(BF4)2 in aHF.

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PubMed2004

New coordination compounds of Cd(AsF6)2 with HF and XeF2.

Two new coordination compounds of cadmium with HF and XeF2 as ligands have been synthesized. Solid white [Cd(HF)](AsF6)2 is obtained from an anhydrous HF (aHF) solution of Cd(AsF6)2. It crystallizes in a monoclinic P2(1)/c space group with a = 9.4687(14) A, b = 9.2724(11) A, c = 10.5503(18) A, beta = 104.887(7) degrees, and Z = 4. The coordination sphere of Cd consists of 7 + 2 fluorine atoms, which are in a capped trigonal-prismatic arrangement. The reaction between Cd(AsF6)2 and XeF(2 in aHF yields a solid white product at room temperature having the composition [Cd(XeF2)4](AsF6)2 after the excess XeF2 and solvent have been removed under dynamic vacuum. [Cd(XeF2)4](AsF6)2 crystallizes in the orthorhombic space group P2(1)2(1)2(1), with a = 8.6482(6) A, b = 13.5555(11) A, c = 16.6312(14) A, and Z = 4. The coordination sphere of Cd consists of eight fluorine atoms, which are at the corners of a trigonal prism with two capped side faces.

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PubMed2004

Th-C60F24.

The regioselective fluorination of Th-C60Br24 with XeF2 in anhydrous HF at 25 degrees C produced Th-C60F24, which is isostructural with Th-C60Br24. The compound, the first example of a fluorofullerene with a noncontiguous pattern of F-bearing sp3 C atoms, was characterized by EI and ESI mass spectrometry and by 19F NMR (single resonance at delta -144 for all 24 F atoms), 13C NMR (two resonances at delta 145.9 (C=C) and delta 83.5 (C-F; JCF = 212 Hz), and FTIR spectroscopy. DFT calculations revealed that at least two other isomers of C60F24 are more stable than Th-C60F24 by >/=280 kJ mol-1, demonstrating that Th-C60F24 is a kinetically stable fluorofullerene.

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PubMed2004

[Mg(XeF(2))(n)()](AsF(6))(2) (n = 4, 2): first compounds of magnesium with XeF(2).

The reaction between Mg(AsF(6))(2) and XeF(2) in anhydrous HF (aHF) at room temperature yields two compounds with XeF(2) bonded directly to the Mg(2+) cation: [Mg(XeF(2))(4)](AsF(6))(2); [Mg(XeF(2))(2)](AsF(6))(2). The 1:4 compound is obtained with excess XeF(2) while the 1:2 compound is prepared from stoichiometric amounts of Mg(AsF(6))(2) and XeF(2). [Mg(XeF(2))(4)](AsF(6))(2) crystallizes in an orthorhombic crystal system, space group P2(1)2(1)2(1), with a = 8.698(15) A, b = 14.517(15) A, c = 15.344(16) A, V = 1937(4) A(3), and Z = 4. The octahedral coordination sphere of Mg consists of one fluorine atom from each of the four XeF(2) molecules and two fluorine atoms from the two AsF(6) units. [Mg(XeF(2))(2)](AsF(6))(2) crystallizes in the orthorhombic crystal system, space group Pbam, with a = 8.9767(10) A, b = 15.1687(18) A, c = 5.3202(6) A, V = 724.42(14) A(3), and Z = 2. The octahedral coordination sphere consists of two fluorine atoms, one from each of the two XeF(2) molecules and four fluorine atoms from the four bridging AsF(6) units.

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PubMed2003

Syntheses, structures and properties of 1-ethyl-3-methylimidazolium salts of fluorocomplex anions.

Fluoroacid-base reactions of a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium fluorohydrogenate (EMIm(HF)2.3F, EMIm = 1-ethyl-3-methylimidazolium cation), and Lewis fluoroacids (BF3, PF5, AsF5, NbF5, TaF5 and WF6) give EMIm salts of the corresponding fluorocomplex anions, EMImBF4, EMImPF6, EMImAsF6, EMImNbF6, EMImTaF6 and EMImWF7, respectively. Attempts to prepare EMImVF6 by both the acid-base reaction of EMIm(HF)2.3F with VF5 and the metathesis of EMImCl with KVF6 failed due to the strong oxidizing power of the pentavalent vanadium, whereas EMImSbF6 was successfully prepared only by the metathesis of EMImCl and KSbF6. EMImBF4, EMImSbF6, EMImNbF6, EMImTaF6 and EMImWF7 are liquids at room temperature whereas EMImPF6 and EMImAsF6 melts at around 330 K. Raman spectra of the obtained salts showed the existence of the EMIm cation and corresponding fluorocomplex anions. IR spectroscopy revealed that strong hydrogen bonds are not observed in these salts. EMImAsF6(mp 326 K) and EMImSbF6(mp 283 K) are isostructural with the previously reported EMImPF6. The melting point of the hexafluorocomplex EMIm salt decreases with the increase of the size of the anion (PF6- < AsF6- < SbF6- <NbF6- approximately TaF6-).

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PubMed2002

Ba(SbF(6))(2).5XeF(2): first xenon(II) compound with barium. Synthesis, vibrational spectra, and crystal structure.

The reaction between Ba(SbF(6))(2) and excess XeF(2) in anhydrous HF at room temperature yields the white solid Ba(SbF(6))(2).5XeF(2) after the excess XeF(2) and the solvent have been removed under vacuum. Ba(SbF(6))(2).5XeF(2) crystallizes in the monoclinic space group C2/m, with a = 13.599(6) A, b = 12.086(4) A, c = 9.732(5) A, beta = 134.305(6) degrees, V = 1144.7 (8) A(3), and Z = 2. The coordination sphere of each barium atom consists of 12 fluorine atoms. The structure consists of alternating layers of Ba(SbF(6))(2).XeF(2) and 4 XeF(2) molecules. The Ba atoms in the Ba(SbF(6))(2).XeF(2) layer are in a nearly rhombic-net array and are linked with trans F-bridging ligands of SbF(6)(-). A XeF(2) molecule is placed in the center of each rhombus of the Ba(2+) array so that its symmetry axis is perpendicular to the plane of the Ba(SbF(6))(2).XeF(2) layer. This layer is linked to its neighbors by a layer of centrosymmetric XeF(2) molecules. Raman spectra are in accord with all XeF(2) molecules being symmetrical.

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PubMed1999

Disproportionation of Ag(II) to Ag(I) and Ag(III) in Fluoride Systems and Syntheses and Structures of (AgF(+))(2)AgF(4)(-)MF(6)(-) Salts (M = As, Sb, Pt, Au, Ru).

Interaction of Ag(+) salts in anhydrous liquid hydrogen fluoride, aHF, with AgF(4)(-) salts gives amorphous red-brown diamagnetic Ag(I)Ag(III)F(4), which transforms exothermally to brown, paramagnetic, microcrystalline Ag(II)F(2) below 0 degrees C. Ag(I)Au(III)F(4) prepared from Ag(+) and AuF(4)(-) in aHF has a tetragonal unit cell and a KBrF(4) type lattice, with a = 5.788(1) Å, c = 10.806(2) Å, and Z = 4. Blue-green Ag(II)FAsF(6) disproportionates in aHF (in the absence of F(-) acceptors) to colorless Ag(I)AsF(6) and a black pseudotrifluoride, (Ag(II)F(+))(2)Ag(III)F(4)(-)AsF(6)(-). The latter and other (AgF)(2)AgF(4)MF(6) salts are also generated by oxidation of AgF(2) or AgF(+) salts in aHF with F(2) or in solutions of O(2)(+)MF(6)(-) salts (M = As, Sb, Pt, Au, Ru). Single crystals of (AgF)(2)AgF(4)AsF(6) were grown from an AgFAsF(6)/AsF(5) solution in aHF standing over AgF(2) or AgFBF(4), with F(2) as the oxidant. They are monoclinic, P2/c, at 20 degrees C, with a = 5.6045(6) Å, b = 5.2567(6) Å, c = 7.8061(8) Å, beta = 96.594(9) degrees, and Z = 1. The structure consists of (AgF)(n)()(n)()(+) chains (F-Ag-F = 180 degrees, Ag-F-Ag = 153.9(11) degrees, Ag-F = 2.003(4) Å), parallel to c, that enclose stacks of alternating AgF(4)(-) and AsF(6)(-), each anion making bridging contact with four Ag(II) cations of the four surrounding chains "caging" them. There is no registry between the ordered array in one "cage" and that in any neighboring "cage". The F-ligand anion bridges between the anions and, with the Ag(II) of the chains, generates a trifluoride-like structure. (AgF)(2)AgF(4)AsF(6) [like other (AgF)(n)()(n)()(+) salts] is a temperature-independent paramagnet except for a Curie "tail" below 50 K.

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