NMR spectroscopic evidence for the intermediacy of XeF(3)(-) in XeF(2)/F(-) exchange, attempted syntheses and thermochemistry of XeF(3)(-) salts, and theoretical studies of the XeF(3)(-) anion.

The existence of the trifluoroxenate(II) anion, XeF(3)(-), had been postulated in a prior NMR study of the exchange between fluoride ion and XeF(2) in CH(3)CN solution. The enthalpy of activation for this exchange, ΔH(⧧), has now been determined by use of single selective inversion (19)F NMR spectroscopy to be 74.1 ± 5.

77Se NMR spectroscopic, DFT MO, and VBT investigations of the reversible dissociation of solid (Se6I2)[AsF6]2.2SO2 in Liquid SO2 to solutions containing 1,4-Se6I2(2+) in equilibrium with Se(n)2+ (n = 4, 8, 10) and seven binary selenium iodine cations: preliminary evidence for 1,1,4,4-Se4Br4(2+) and cyclo-Se7Br+.

The composition of a complex equilibrium mixture formed upon dissolution of (Se(6)I(2))[AsF(6)](2).2SO(2) in SO(2)(l) was studied by (77)Se NMR spectroscopy at -70 degrees C with both natural-abundance and enriched (77)Se-isotope samples (enrichment 92%). Both the natural-abundance and enriched NMR spectra showed the presence of previously known cations 1,4-Se(6)I(2)(2+), SeI(3)(+), 1,1,4,4-Se(4)I(4)(2+), Se(10)(2+), Se(8)(2+), and Se(4)(2+).

Accounting for the differences in the structures and relative energies of the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I4 2+, the Se-I pi-bonded Se2I4 2+, and their higher-energy isomers by AIM, MO, NBO, and VB methodologies.

The bonding in the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I42+ (three sigma + two pi bonds), the Se-I pi-bonded Se2I42+ (four sigma + one pi bonds), and their higher-energy isomers have been studied using modern DFT and ab initio calculations and theoretical analysis methods: atoms in molecules (AIM), molecular orbital (MO), natural bond orbital (NBO), and valence bond (VB) analyses, giving their relative energies, theoretical bond orders, and atomic charges. The aim of this work was to seek theory-based answers to four main questions: (1) Are the previously proposed simple pi*-pi* bonding models valid for S2I42+ and Se2I42+? (2) What accounts for the difference in the structures of S2I42+ and Se2I42+? (3) Why are the classically bonded isolobal P2I4 and As2I4 structures not adopted? (4) Is the high experimentally observed S-S bond order supported by theoretical bond orders, and how does it relate to high bond orders between other heavier main group elements? The AIM analysis confirmed the high bond orders and established that the weak bonds observed in S2I42+ and Se2I42+ are real and the bonding in these cations is covalent in nature. The full MO analysis confirmed that S2I42+ contains three sigma and two pi bonds, that the positive charge is essentially equally distributed over all atoms, that the bonding between S2 and two I2+ units in S2I42+ is best described by two mutually perpendicular 4c2e pi*-pi* bonds, and that in Se2I42+, two SeI2+ moieties are joined by a 6c2e pi*-pi* bond, both in agreement with previously suggested models.

Syntheses and X-ray crystal structures of alpha- and beta-[XeO2F][SbF6], [XeO2F][AsF6], [FO2XeFXeO2F][AsF6], and [XeF5][SbF6)].XeOF4 and computational studies of the XeO2F+ and FO2XeFXeO2F+ cations and related species.

Reactions of XeO2F2 with the strong fluoride ion acceptors, AsF5 and SbF5, in anhydrous HF solvent give rise to alpha- and beta-[XeO2F][SbF6], [XeO2F][AsF6], and [FO2XeFXeO2F][AsF6]. The crystal structures of alpha-[XeO2F][SbF6] and [XeO2F][AsF6] consist of trigonal-pyramidal XeO2F+ cations, which are consistent with an AXY2E VSEPR arrangement, and distorted octahedral MF6- (M = As, Sb) anions. The beta-phase of [XeO2F][SbF6] is a tetramer in which the xenon atoms of four XeO2F+ cations and the antimony atoms of four SbF6- anions are positioned at alternate corners of a cube.

Syntheses; 77Se, 203Tl, and 205Tl NMR; and theoretical studies of the Tl2Se6(6-), Tl3Se6(5-), and Tl3Se7(5-) anions and the X-ray crystal structures of [2,2,2-crypt-Na]4[Tl4Se8].en and [2,2,2-crypt-Na]2[Tl2Se4](infinity)1.en.

The 2,2,2-crypt salts of the Tl4Se8(4-) and [Tl2Se4(2-)]infinity1 anions have been obtained by extraction of the ternary alloy NaTl0.5Se in ethylenediamine (en) in the presence of 2,2,2-crypt and 18-crown-6 followed by vapor-phase diffusion of THF into the en extract. The [2,2,2-crypt-Na]4[Tl4Se8].

A computational and experimental study of the structures and Raman and 77Se NMR spectra of SeX3+ and SeX2 (X = Cl, Br, I): FT-Raman spectrum of (SeI3)[AsF6].

The ability of MP2, B3PW91 and PBE0 methods to produce reliable predictions in structural and spectroscopic properties of small selenium-halogen molecules and cations has been demonstrated by using 6-311G(d) and cc-pVTZ basis sets. Optimized structures and vibrational frequencies agree closely with the experimental information, where available. Raman intensities are also well reproduced at all levels of theory.

X-ray crystal structures of [XF(6)][Sb(2)F(11)] (X = Cl, Br, I); (35,37)Cl, (79,81)Br, and (127)I NMR studies and electronic structure calculations of the XF(6)(+) cations.

The single-crystal X-ray structures of [XF(6)][Sb(2)F(11)] (X = Cl, Br, I) have been determined and represent the first detailed crystallographic study of salts containing the XF(6)(+) cations. The three salts are isomorphous and crystallize in the monoclinic space group P2(1)/n with Z = 4: [ClF(6)][Sb(2)F(11)], a = 11.824(2) A, b = 8.

The syntheses of carbocations by use of the noble-gas oxidant, [XeOTeF5][Sb(OTeF5)6]: the syntheses and characterization of the CX3+ (X = Cl, Br, OTeF5) and CBr(OTeF5)2+ cations and theoretical studies of CX3+ and BX3 (X = F, Cl, Br, I, OTeF5).

The CCl(3)(+) and CBr(3)(+) cations have been synthesized by oxidation of a halide ligand of CCl(4) and CBr(4) at -78 degrees C in SO(2)ClF solvent by use of [XeOTeF(5)][Sb(OTeF(5))(6)]. The CBr(3)(+) cation reacts further with BrOTeF(5) to give CBr(OTeF(5))(2)(+), C(OTeF(5))(3)(+), and Br(2). The [XeOTeF(5)][Sb(OTeF(5))(6)] salt was also found to react with BrOTeF(5) in SO(2)ClF solvent at -78 degrees C to give the Br(OTeF(5))(2)(+) cation.

Conformations and energetics of sulfur and selenium diimides.

The geometries and energetics of different conformations of sulfur and selenium diimides E(NR)(2) (E = S, Se; R = H, Me, (t)Bu, C(6)H(3)Me(2)-2,6, SiMe(3)) have been studied by using various ab initio and DFT molecular orbital techniques. The syn,syn conformation is found to be most stable for parent E(NH)(2), but in general, the preferred molecular conformation for substituted chalcogen diimides is syn,anti. In the case of E(NH)(2) the present calculations further confirm that syn,syn and syn,anti conformations lie energetically close to each other.

Theoretical and Experimental Studies of Six-Membered Selenium-Sulfur Nitrides Se(x)()S(4)(-)(x)()N(2) (x = 0-4). Preparation of S(4)N(2) and SeS(3)N(2) by the Reaction of Bis[bis(trimethylsilyl)amino]sulfane with Chalcogen Chlorides.

The reaction of [(Me(3)Si)(2)N](2)S with equimolar amounts of SCl(2) and S(2)Cl(2) produces S(4)N(2) in a good yield. The reaction of [(Me(3)Si)(2)N](2)S with a 3:1:1 mixture of S(2)Cl(2), Se(2)Cl(2), and SeCl(4) yields a dark brown-red insoluble material that was inferred to be mainly SSeSNSN on the basis of the elemental analysis, mass spectroscopy, vibrational analysis, and NMR spectroscopy. Attempts to prepare selenium-rich species resulted in the formation of elemental selenium or Se(3)N(2)Cl(2).