GOLD ATOM CHEMISTRY; SYNTHESIS AND CHARACTERIZATION OF BINARY GOLD CARBONYLS Au(CO)$^{n} (WHERE n = 1 OR 2)$ IN LOW TEMPERATURE MATRICES; SPECTROSCOPIC EVIDENCE FOR ISOCARBONYL-CAR BONYL GOLD, A LINKAGE ISOMER OF BIS-CARBONYL GOLD

Abstract

The cocondensation reaction of Au atoms with CO/M mixtures (where $M = Ne$, Ar, Kr, or Xe) at $6-10^\circ K$ leads to the formation of authentic binary gold carbonyls $Au(CO)_{n}$ (where $n = 1$ or 2). These complexes were characterized using metal and ligand concentration studies, $^{12}C^{16}O/^{13}C^{16}O/M$ isotpic substitution and warm up experiments in conjunction with matrix infrared and uv-visible spectroscopy as well as isotope frequency and intensity calculations. The infrared data for bis-carbonyl gold favors a linear, symmetrical $D_{\infty b}$ structure. Detailed investigations of the complexes in inert gas matrices revealed a variety of interesting site effects and matrix induced frequency shifts. Particularly noteworthy were the unusual vibrational isotope patterns observed for the product formed when gold atoms were deposited with $^{12}C^{16}O/^{13}C^{16}O, ^{12}C^{16}O/^{12}C^{18}O$ and $^{12}C^{16}O/^{13}C^{18}O$ mixtures. Ten distinct, mixed isotopic molecules containing non-equivalent carbonyl ligands were identified. A reasonable interpretation of the isotopic shifts was in terms of an isocarbonyl-carbonyl gold complex (OC) Au (OC), a linkage isomer of bis-carbonyl gold. The existence of the linkage isomer is thought to be a consequence of the orientational requirements of the CO molecules in the fcc lattice of crystalline carbon monoxide $(aL-CO)$ rather than an inherent preference for the isocarbony1 isomer. Support for this idea stems from the ability to produce (OC) Au(OC) in solid $\alpha-N_{2}$. Additional information concerning the bonding and electronic properties of (OC) Au(CO) and (OC) Au (OC) was obtained from their uv-visible spectra in Ar/CO and CO matrices respectively. In this context, the results of extended H\""{u}ckel molecular orbital calculations proved to be quite helpful for understanding the differences between a C- and O- bonded carbonyl ligand.