Knowledge Bank

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, $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}C16O/13C16O/M$ 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 $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}C16O/13C16O,12C16O/12C18O$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}C16O/13C18O$ 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 $\alpha -N2$. 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.