Boris Žemva

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-

A study on the formation mechanism of graphite fluorides by Raman spectroscopy

Abstract Raman spectra were measured of highly fluorinated graphite samples prepared at room temperature, 380 and 515xa0°C. C x F prepared at room temperature showed a novel downshifted band at 1555–1542xa0cm −1 along with G band at 1593–1583xa0cm −1 . Similar behavior is also observed for samples prepared at 380 and 515xa0°C at early stages of fluorination, after which the Raman shifts completely disappeared. Raman spectra as well as X-ray diffraction (XRD) analysis suggest that graphite fluorides, (CF) n and (C 2 F) n are formed via fluorine-intercalated phase with planar graphene layers.

Access to the structures of fluoromagnesium compounds: synthesis and structural characterization of the β-diketiminato magnesium fluoride [{CH(CMeNAr)2}Mg(μ-F)(THF)]2·toluene

Abstract β-Diketiminato magnesium fluoride [{CH(CMeNAr) 2 }Mg(μ-F)(THF)] 2 ·toluene (Ar=2,6-i-Pr 2 C 6 H 3 , 2 ·toluene) was synthesized. The molecular structure of 2 revealed for the first time, the double fluoro bridge feature between the two magnesium atoms with a typical Mgue5f8F bond length (average 1.95xa0A).

Coordination compounds with XeF2, AsF3 and HF as ligands to metal ions: a review of reaction systematics, Raman spectra and metal, fluoro-ligand polyhedra

Abstract The reactions between Ln(AsF 6 ) 3 (Ln: lanthanide) and excess of XeF 2 in anhydrous HF (aHF) as a solvent yield coordination compounds [Ln(XeF 2 ) 3 ](AsF 6 ) 3 or LnF 3 together with Xe 2 F 3 AsF 6 or mixtures of all mentioned products depending on the fluorobasicity of XeF 2 and LnF 3 along the series. XeF 2 in a basic aHF is able to oxidize Pr 3+ to Pr 4+ besides Ce 3+ to Ce 4+ and Tb 3+ to Tb 4+ . The tetrafluorides obtained are weaker fluorobases as XeF 2 and are immediately exchanged with XeF 2 yielding Xe 2 F 3 AsF 6 and LnF 4 . The analogous reaction between Ln(BiF 6 ) 3 and XeF 2 in aHF yields [Ln(XeF 2 ) 3 ](BiF 6 ) 3 , Ln: La, Nd. Raman spectra of the compounds [Ln(XeF 2 ) n ](AF 6 ) 3 (A: As, Bi) show that no XeF + salts are formed. The interaction of XeF 2 with metal ion is covalent over the fluorine bridge. Analogous reactions of Ln(AsF 6 ) 3 with AsF 3 in aHF yield [Ln(AsF 3 ) 3 ](AsF 6 ) 3 which are stable in a dynamic vacuum at temperatures lower than 233 K. In reactions between M(AF 6 ) 2 (M: alkaline earth metal and Pb, A: As, Sb) and XeF 2 in aHF as a solvent, compounds of the type [M(XeF 2 ) n ](AF 6 ) 2 were synthesized. Analogous reactions with AsF 3 yield coordination compounds of the type [M(AsF 3 ) n ](AsF 6 ) 2 . During the preparation of M x (AsF 6 ) x (M: metal in oxidation state x +) by the reaction between metal fluoride and excess of AsF 5 in aHF it was found that HF could also act as a ligand to the metal ions (e.g. Ca(HF)(AsF 6 ) 2 ).

Novel oxonium compounds of lanthanoids: synthesis of (H3O)3La2F(AsF6)8, and syntheses and crystal structures of (H3O)8La2F(AsF6)13 and (H3O)4La2F(AsF3)2(AsF6)9

Abstract Reactions of Ln 2 O 3 with AsF 5 in aHF (Ln=La–Lu, aHF=anhydrous hydrogen fluoride) yield solutions of H 3 O + , solvated Ln 3+ and AsF 6 − ions. Very similar solutions of these ions may be obtained from combination of various other starting materials, e.g. LnF 3 –H 2 O–AsF 5 –aHF, LnF x (AsF 6 ) 3− x –H 3 OAsF 6 –aHF. From such solutions a new type of oxonium compounds with general formula (H 3 O) x Ln y F z (AsF 6 ) x +3 y − z have been isolated at ambient temperature. (H 3 O) 3 La 2 F(AsF 6 ) 8 was obtained as a white powder from the solution of La 2 O 3 dissolved in AsF 5 –aHF after pumping off all volatiles at room temperature. Colourless crystals of (H 3 O) 8 La 2 F(AsF 6 ) 13 were prepared by slow static evaporation from a solution obtained after solvolysis of solid (H 3 O) 3 La 2 F(AsF 6 ) 8 in aHF at ambient conditions. Colourless crystals of (H 3 O) 4 La 2 F(AsF 3 ) 2 (AsF 6 ) 9 were prepared by the reaction of La 2 O 3 with AsF 5 and aHF under solvothermal conditions above the critical temperature of AsF 5 . Similar reactions of other oxides Ln 2 O 3 (Ln=Nd, Sm, Gd, Dy, Ho, Tm) have also been studied. (H 3 O) 8 La 2 F(AsF 6 ) 13 crystallises in the monoclinic space group P 2 1 / c (no. 14 ) with a =1079.3(3)xa0pm, b =2859.0(7)xa0pm, c =1068.0(3)xa0pm, β =109.310(8)°, and Z =2. (H 3 O) 4 La 2 F(AsF 3 ) 2 (AsF 6 ) 9 crystallises in the triclinic space group P 1 (no. 2) with a =1064.8(3)xa0pm, b =1073.3(4)xa0pm, c =1213.9(3)xa0pm, α =75.53(2)°, β =64.79(2)°, γ =70.07(2)°, and Z =1. Both structures are closely related with zig-zag chains of alternating La 2 F and AsF 6 units resembling the main feature. Oxonium ions are arranged among such anionic chains.

Reaction of silver(I) and (II) fluorides with C60: thermodynamic control over fluorination level

Silver(I) fluoride is shown to be a weak fluorinating agent (FA) for C-60 and gives mainly C60F18. Fluorination with silver(II) fluoride yields C60F44, a new compound, as the predominant product (> 80% in the crude). Fluorination degree of fullerenes in reaction with binary metal fluorides is found to be mainly thermodynamically controlled. The correlation between the level of C-60 fluorination and oxidising fluorinating strength of the metal fluorides used for fluorofullerene preparations is discussed, permitting development of a self-consistent quantitative scale for inorganic FAs.

Synthesis and crystal structures of two new lead(II) hexafluoroarsenates(V)

Abstract In the system PbF2/AsF5/anhydrous hydrogen fluoride (aHF) two new lead(II) hexafluoroarsenates(V) Pb(HF)(AsF6)2 and PbFAsF6 were isolated. Pb(HF)(AsF6)2 is formed when the molar ratio AsF5:PbF2 is 2 or higher. It crystallizes in the space group Pbcn with a=1058.3(3)xa0pm, b=1520.9(6)xa0pm, c=1079.4(3)xa0pm, V=1.7374(10)xa0nm3 and Z=8. The HF molecule is directly connected to the Pb center, eight fluorine atoms from three different AsF6− ions (Pb–F distances ranging from 248(4) to 276(2)xa0pm) and one further fluorine at 306(3)xa0pm complete the coordination sphere. PbFAsF6 is obtained when equimolar amounts of PbF2 and AsF5 react in aHF. PbFAsF6 crystallizes in the space group P 1 with: a=466.10(10)xa0pm, b=723.70(10)xa0pm, c=747.40(10)xa0pm, α=105.930(10)°, β=101.49(2)°, γ=90.660(10)°, V=0.23698(7)xa0nm3 and Z=2. The basic unit in the structure of PbF(AsF6) consists of a four-membered ring of two Pb and two F atoms. The Pb atoms in the ring are further connected by two AsF6− units via cis-fluorine bridges, thus forming a [PbF(AsF6)]2 cluster, which interacts by additional Pb–F bonds thus forming a ribbon-like polymer.

Transition metal sulfur dioxide hexafluoroarsenates and hexafluoroantimonates

Abstract The preparation and characterization by X-ray crystallography of transition metal sulfur dioxide hexafluoroarsenates of the general formula [M(SO2)x](AsF6)2 1 (1a: M=Mn, x=2; 1c: M=Co, x=4; 1e: M=Cu, x=4) and the hexafluoroantimonate [Co(SO2)2](SbF6)2 3 is reported. The structural features of the compounds mentioned are compared with those of [Fe(SO2)4](AsF6)2 (1b) and [Ni(SO2)6](AsF6)2 (1d), reported previously. The structural diversity of transition metal sulfur dioxide complexes is discussed.

Raman scattering study of graphite fluorides

Highly fluorinated C X F samples (1<x<2), prepared at room temperature and 515°C, were analysed by Raman and IR absorption spectroscopies. The effect of fluorination on structural disordering is analysed by observing both the Raman allowed E 2g2 phonon mode at 1580 cm −1 and the disorder induced phonon mode at ∼1360 cm −1 . Raman spectra suggested the coexistence of C 2 F and C 1 F phases.

Electrochemical Properties of Natural Graphite Fluorinated by ClF3 and NF3 in Propylene Carbonate-Containing Solvent

Surface fluorination of natural graphite samples with average particle sizes of 5, 10, and 15 μm (NG5, NG10, and NG15 μm) was performed by ClF 3 and NF 3 (1 X 10 5 Pa) at 200 and 300°C for 5 min, and charge/discharge behavior of fluorinated samples was investigated in 1 mol/dm 3 LiClO 4 -ethylene carbonate (EC)/diethyl carbonate (DEC)/propylene carbonate (PC) (1:1:1 in volume). Mesopores with a diameter of 2 nm were increased by the surface fluorination, while those with diameters of 2.5 and 3 nm were reduced. Surface disorder of natural graphite samples also increased with increasing fluorination temperature and particle size. These surface structure changes by surface fluorination would have reduced the decomposition of PC, leading to an increase in first coulombic efficiencies. The increase in first coulombic efficiencies was larger at a current density of 150 mA/g than 60 mA/g, reaching ca. 10 and 20% for NG10 and NG15 μm fluorinated by ClF 3 .