BIS(CARBONYL)GOLD(I) UNDECAFLUORODIANTIMONATE(V), [AU(CO)2][SB2F11] - SYNTHESIS, VIBRATIONAL AND C-13 NMR-STUDY, AND THE MOLECULAR-STRUCTURE OF BIS(ACETONITRILE)GOLD(I) HEXAFLUOROANTIMONATE(V), [AU(NCCH3)2][SBF6]

The synthesis of the bis(carbonyl)gold(I) salt, [Au(CO)2] [Sb2F11], is achieved in a two-step procedure: the reduction of gold(III) fluorosulfate, Au(SO3F)3, in HSO3F to give AU(CO)SO3F as an intermediate, followed by solvolysis in liquid antimony(V) fluoride in the presence of carbon monoxide. The use of (CO)-C-13 or (CO)-O-18 permits the synthesis of the corresponding isotopically labeled salts. The compound is thermally stable up to 130-degrees-C. The cation has D(infinity h) symmetry, and all seven fundamentals, three Raman and four IR active modes, are observed. A normal coordinate analysis (NCA) and general valence force-field (GVFF) calculations are carried out and allow comparison to the isoelectronic and isosteric molecular species Hg(CN)2 and [Au(CN)2]-. The near absence of gold to carbon pi-back donation in [Au(CO)2]+ is manifested in strong carbon-oxygen bonds and consequently rather weak gold-carbon bonds, reflected in the highest CO-stretching frequencies so far observed for a metal carbonyl derivative with 2254 (nu1) and 2217 (nu3) cm-1 and a stretching force constant of 20.1 X 10(2) Nm-1. In the C-13 NMR spectrum a single-line resonance at 174 ppm is attributed to ([Au(CO)2]+)-C-13, while the ([Au(CO)]+)-C-13 chemical shift changes from 162 ppm in HSO3F to 158 ppm in magic acid (HSO3F/SbF5). The resonances for ([Au(CO)2]+)-C-13 and ([Au(CO)]+)-C-13 in the same solution are found to undergo coalescence at elevated temperature indicative of slow CO exchange. The coalescence temperature is solvent dependent, 325 K in HSO3F and 395 K in the more dilute HSO3F/SbF5 mixture. Attempts to recrystallize [Au(CO)2] [Sb2F11] from acetonitrile result in the formation of single crystals of [Au(NCCH3)2][SbF6] instead. The compound crystallizes in a cubic unit cell, space group Pa3BAR, with a = 10.250 (2) angstrom and Z = 4. The structure was determined by Patterson and Fourier methods and refined by least-squares techniques to R = 0.023 and R(w) = 0.024 for 147 reflections with I > 3sigma(I). The crystal contains linear [Au(NCCH3)2]+ cations and octahedral [SbF6]- anions, with normal dimensions.