X-Ray Crystal Structures of Xe(II)-N and Xe(II)-O Bonded Compounds, and the Synthesis of OTeF5 Derivatives of As(III) and Sb(III)

Abstract

<p>The chemistry of xenon(II) has been extended by the low-temperature X-ray structure determinations of the Xe-N bonded adduct salts, HC≡N-XeF+AsF6-, CH3C≡N-XeF+AsF6-·HF, (CH3)3CC≡N-XeF+AsF6-, s-C3F3N2N-XeF+AsF6-·2.5BrF5, C5F5N-XeF+AsF6-·2.5BrF5, and F5TeN(H)Xe+AsF6-, and the Xe-0 bonded compounds, F5ChOXe+AsF6- and Xe(OChF5)2 (Ch = Te, Se).</p> <p>The thermally unstable Xe-N bonded salts represent classes of compounds in which xenon(II) is directly bonded to formally sp-, sp2-, or sp3- hybridized nitrogen atoms. The R-C≡N-XeF+AsF6- (R = H, CH3, (CH3)3C) salts were synthesized by the low-temperature reaction of the nitrogen base with XeF+AsF6- in HF. The C5F5N-XeF+AsF6-·2.5BrF5 and F5TeN(H)Xe+AsF6- compounds were prepared by the reaction of the N-protonated bases with XeF2 in BrF5 and with XeF+AsF6- in HF, respectively. The s-C3F3N2N-XeF+AsF6-·2.5BrF5 salt was prepared by the direct interaction of s-C3F3N3 with XeF+AsF6- at room temperature and subsequent recrystallization from BrF5. The covalent nature of the Xe-N bonds was observed to increase in the order: s-C3F3N2N-XeF+AsF6-·2.5BrF5 (2.316(6) Å) < C5F5N-XeF+AsF6-·2.5BrF5 (2.287(7) Å) < HC≡N-XeF+AsF6- (2.235(3) Å) < (CH3)3CC≡N-XeF+AsF6- (2.212(4) Å) < CH3C≡N-XeF+AsF6-·HF (2.179(7) Å) < F5TeN(H)Xe+ AsF6- (2.044(4) Å), indicating that s-C3F3N2N-XeF+ AsF6-·2.5BrF5 contains the most ionic Xe-N bond in this series. It was also observed that as the covalent nature of the Xe-N bond increases, the Xe-F bond becomes more ionic. The Xray crystal structures of HCNH+AsF6-, F5TeNH3+AsF6-, and F5TeNH2 were also determined and provided comparisons with those of HC≡N-XeF+ AsF6- and F5TeN(H)Xe+AsF6-, respectively.</p> <p>The X-ray crystal structures of the XeOChF5+AsF6- salts have been determined and are isostructural and disordered. The structure of Xe(OSeF5)2 is in agreement with a previous structure report, but is now assigned to the correct space group. The single crystal X-ray structure of Xe(OTeF5)2 was determined for the first time and contradicts an earlier published cell determination of this compound. The structures of XeOChF5+AsF6- and Xe(OChF5)2, which are analogs of XeF+ and XeF2, respectively, confirm that the OChF5 groups have lower electronegativities than F. When compared with the structure of F5TeN(H)Xe+AsF6-, which is isolobal with XeOChF5+AsF6-, it was determined that the relative electronegativities of these groups, and subsequent Lewis acidities of the cations, F5TeN(H)Xe+, XeOChF5+, and XeF+, increase in the order: F5TeN(H) > OSeF5 > OTeF5 >F.</p> <p>Local density functional theory (LDFT/DZVP) calculations which were done for F5TeN(H)Xe+AsF6-, F5TeNH3+AsF6-, F5TeNH2, and XeOChF5+AsF6-, reproduce the structures and have been used to assign their vibrational spectra. Only the calculated vibrational spectra for XeOChF5+AsF6- are discussed in this Thesis.</p> <p>The OTeF5 chemistry of As and Sb has also been extended by the syntheses and detailed structural characterizations by 19F and 125Te NMR spectroscopy and by Raman spectroscopy of the new pnicogen anions, Pn(OTeF5)4-(Pn = Sb, As), as their N(CH3)4+ and N(CH2CH3)4+ salts. The As(OTeF5)4- anion was found to be thermally less stable in CH3CN and SO2ClF solvents when compared to the analogous antimony anion. Both anions have trigonal-bipyramidal AX5E VSEPR geometries with two equatorial and two axial OTeF5 ligands that undergo intermolecular exchange in solution by Berry pseudorotation. However, the exchange could not be slowed down sufficiently on the NMR time scale to observe separate environments due to the freezing points of the solvents used. An equilibrium was also observed to occur between Sb(OTeF5)4-, Sb(OTeF5)3, and OTeF5- in CH3CH2CN solvent. All attempts to crystallize Sb(OTeF5)4- were unsuccessful and produced the less soluble, but novel, Sb(OTeF5)5 2- anion instead, whose preliminary disordered X-ray crystal structure is reported in this Thesis.</p>