Jeremy C. P. Sanders

Krypton bis[pentafluoro-oxotellurate(VI)], Kr(OTeF5)2, the first example of a Kr–O bond

Krypton bis[pentafluoro-oxotellurate(VI)] provides the first example of a species containing a krypton–oxygen bond and has been prepared by the reaction of KrF2 with natural abundance and 17O-enriched B(OTeF5)3 at –90 to –112 °C in SO2CIF solvent; characterization of the thermally unstable Kr(OTeF5)2 and its decomposition products has been achieved using 19F and 17O n.m.r. spectroscopy.

Structural Aspects of Spin-Spin Coupling in Multi-NMR Spectroscopy

The observation of spin-spin coupling in NMR spectra provides a powerful method for structural elucidation. In this review the direct measurement of J is described for primarily first-order systems. The analysis of spin-spin coupling patterns is outlined for cases in which a nucleus A is coupled to a spin-1/2 nucleus B under the conditions of different natural abundance of B. The use of reduced coupling constants and the importance of relativistic effects for coupling between heavy nuclides are exemplified. The conditions under which spin-spin coupling to quadrupolar nuclei may be observed are discussed and illustrated. The effects of quadrupolar relaxation on the spectra of spin-1/2 nuclei and the analysis of the spectra in such situations are described. The less well-known phenomena, namely, isotope effects on the spin-spin coupling constant and the anisotropy of J are briefly discussed at the end of the chapter. Throughout the text numerous examples are provided and illustrated.

Structural characterization of hypervalent fluoride and oxofluoride derivatives of xenon and tellurium and iodine

Abstract The study of fluoro- and oxofluoro-anions and cations having coordination numbers higher than six has been of particular interest and is exemplified by the fluoride ion donor and electron pair acceptor properties of the oxofluorides of xenon. The X-ray crystal structure of XeOF 3 + SbF 6 − has been determined. The XeOF 3 + cation is shown to have two fluorine bridges to neighboring SbF 6 − anions, resulting in an AX 6 E VSEPR arrangement around xenon in the solid state. The solution 17 O NMR spectrum along with the 17 O/ 18 O isotope shift ratio in the 129 Xe spectrum of the XeOF 3 + cation have also been obtained. The fluoride ion donor properties of XeOF 2 and the formation of the XeOF + cation are also discussed. The electron pair acceptor properties of XeOF 4 , XeOF 2 and XeO 3 in the presence of nitrogen bases have been investigated by NMR spectroscopy. The XeOF 4 ·CH 3 CN adduct has been isolated as a crystalline solid and its structure also appears to be best represented as a distorted octahedral (AX 6 E) arrangement. In collaboration with Dr. K.O. Christe and Dr. W.W. Wilson (Rockwell International), a number of hypervalent anions having coordination numbers exceeding six have been prepared and characterized. The IOF 6 − anion has been characterized as its N(CH 3 ) 4 + salt by X-ray crystallography, vibrational spectroscopy and in solution by NMR spectroscopy. The X-ray structure shows that the anion is distorted from C 5v point symmetry by means of a puckering of the five fluorines in its equatorial plane. The structures of the N(CH 3 ) 4 + salts of the TeOF 6 2− , XeOF 5 − , XeF 7 − and TeF 7 − anions will also be described. The Lewis acid properties of XeF + and XeOTeF 5 + have been investigated in the presence of the nitrogen base F 5 TeNH 2 . The novel XeN bonded F 5 TeN(H)Xe + and F 5 TeN(H)XeNCH + cations have been synthesized in anhydrous HF and characterized by 1 H, 15 N, 19 F, 125 Te and 129 Xe NMR spectroscopy.

New OTeF5 derivatives of xenon (IV), xenon (VI) and tellurium (VI).

Abstract In view of the recent synthesis and characterization of the novel pentagonal planar (D5h) XeF5− anion, it was of interest to attempt the synthesis of the corresponding OTeF5 substituted anion, Xe(OTeF5) 5−, as well as the series of mixed F/OTeF5 anions, XeFn(OTeF5)5−n− (n = 1 − 4). So far all efforts to prepare these anions have failed, rather reactions of Xe (OTeF5)4 with N(CH3) 4+F− or N(CH3)4+OTeF5− in CH3CN have resulted in the formation of the new Xe(IV) oxo-species OXeF(OTeF5) and OXe(OTeF5)2. These species, together with the previously known OXeF2, have been characterized in solution for the first time by 129Xe and 19F NMR spectroscopy. Analogous reactions with OTeF5 derivatives of Xe(VI) and Te(VI) will also be discussed.

Lewis acid behavior of xenon (II) cations and the synthesis and characterization of fluoro- and oxofluoro-xenon anions at the limits of coordination.

Abstract By taking advantage of the Lewis acid properties of the XeF+ and KrF+ cations, it has been possible to prepare a diverse range of noble-gas adduct cations; FXeL+, FKrNCH+ and FKrNCRF+ (L  HCN, RCN, RFCN, C5F5N, sC3F3N3). The adduct salts have stabilities which range from explosive at −60 °C for FKrNCH+AsF6− (the first example of a KrN bond), to stable at room temperature for sC3F3N2NXeF+AsF6− and have been characterized by multi-NMR spectroscopy and Raman spectroscopy. We have recently extended this work to the related noble-gas cations XeOTeF5+ and XeOSeF5+, to yield the first examples of OXeN linkages, and to the inorganic base F3SN. The adduct cation FXeNSF3+ undergoes successive additions of HF to the NS bond in anhydrous HF to give the adduct cations FXeN(H)SF4+ and FXeN(H2)SF5+. The FXeN(H2)TeF5+ cation has also been synthesized. The study of fluoro-anions having coordination numbers higher than six and, in particular, those involving at the same time free valence electron pairs, have recently received considerable interest. To a large extent, these studies have been greatly facilitated by the realization that anhydrous N(CH3)4+F− is an excellent reagent for the preparation of novel, high-oxidation state complex fluoride or oxofluoride anions. We have recently synthesized (CH3)4N+XeF5− by the reaction of stoichiometric amounts of XeF4 and N(CH3)4+F− in dry CH3CN. The salt was fully characterized by Raman spectroscopy, 19F and 129Xe NMR spectroscopy and X-ray crystallography. The XeF5− anion has a pentagonal planar (D5h) structure with five equivalent fluorines and is of considreable significance as it represents the first example of an AX5E2 (E = valence electron lone pair) system. The syntheses and structural characterization of other high-coordination number hypervalent fluoro- and oxofluoro- anions of xenon will also be discussed, i.e., XeF5O−, XeF7−, XeOF3−, XeO2F3−.

Novel bonding situations in noble-gas chemistry

Abstract We are currently in a much better position to understand the factors underlying noble-gas compound formation. This has recently been accomplished by synthesizing over two dozen new xenon and krypton compounds in which the noble gas is bonded to organic fragments through nitrogen. The ligand groups consist of perfluoropyridines, nitriles and s-trifluorotrizine adducted to the lewis acid cations XeF + and KrF + . The chemistry represents the first time the strongly oxidizing XeF + and KrF + cations have been bonded to organic moieties. The formation of HCN-XeF + AsF 6 - and several organic nitrile cation RCNXeF + ) led to successful attempts to bond one of the best fuels known, HCN, to what is one of the strongest oxidants known, KrF + . Although the HCN-KrF + AsF 6 - salt is a violent detonator in the solid state at ca. -60 °C, it has been fully characterized by multi-NMR ( 1 H, 13 C, 15 N and 19 F) and low-temperature Raman spectroscopy. Three further examples of krypton-nitrogen bonded species in which the KrF + cation is bonded to an organic base have also been prepared, i.e. , R F CNKrF + (R F = CF 3 , C 2 F 3 , n-C 3 F 7 ). More recently, this chemistry has been extended to the XeOTeF 5 + cation. Representative nitrile, perfluoropyridine and S- trifluorotriazine adduct cations have been prepared. The synthesis of a number of these adduct cations with Sb(OTeF 3 ) 6 - as the counter ion offers the possibility of synthesizing thermally less stable XeOTeF 3 + adduct cations at low temperature in low polarity solvents. This has become possible owing to the high solubility of the novel precursor salt, XeOTeF 5 + Sb(OTeF 5 ) 6 - . Our recent discovery of the first krypton-nitrogen bonds and the previous existence of Kr-F bonded species have served to underscore the apparent anomalous non-existence of Kr-O bonds. We have recently put a considerable amount of effort into trying to synthesize the first such example of a Kr-O bond and will present the results of these findings.

Synthesis and characterization of XeOTeF5+Sb(OTeF5)6-

Abstract The XeOTeF 5 + cation has been characterized previously as the AsF 6 - and Sb 2 F 11 - salts, however investigation of the chemistry of XeOTeF 5 + has been limited by the insolubility of these two salts in inert solvents. The new salt, XeOTeF 5 + Sb(OTeF 5 ) 6 - , has been synthesized and represents the first example of a salt containing both an OTeF 5 substituted cation and anion. The compound is a stable pale-orange solid and has been characterized by 129 Xe, 121 Sb and 19 F NMR and Raman spectroscopy. The high solubility of XeOTeF 5 + Sb(OTeF 5 ) 6 - in inert low-polarity solvents affords new possibilities for investigating the chemistry of the XeOTeF 5 + cation. The Lewis acid properties of XeOTeF 5 + will be described.