Between Different Metals in Carbonyls and Their Derivatives

Between Different Metals in Carbonyls and Their Derivatives... 

Between Different Metals in Carbonyls and Their Derivatives 9.2.5.4. By Reactions of a Metal Halide with a Metal Carbonyl Anion... 

These and related methods of structure prediction depend upon the allocation of specific electron counts to different framework geometries and these applications have been very successful in assigning structures to cluster carbonyls and their derivatives. However, for the higher polynuclear carbonyls as the molecularity of the compounds increases the predictive power of the theories becomes less decisive in differentiating between alternative structures. In essence the Wade-Mingos approach assumes that the frontier orbitals of the complex primarily involve metal orbitals so that any variation in the electron occupation will be reffected in a structural change in the metal framework. The Wade theory also requires that the structure of the complexes are based on triangulated polyhedra as found for the boron hydrides. 

It has become apparent from the observation of vCO above 2200 cm l and from stretching force constants above 20 x 10 Nm"l for [Au(CO)2] " and [Pt(CO)4]2" ", diat these binary carbonyl cations differ drastically from classical transition-metal carbonyls with terminal CO groups, where vCO is foxmd in the general range of 2125 to 1850 cm (79, 80) and force constants usually between 15 and 1710 Nm l. It is obvious that Tc-backdonation, which is essential in transition-metal carbonyls (81), must be absent or substantially reduced and that carbon monoxide does not function as a 71-acceptor, but rather as a a-donor in noble-metal carbonyl cations and their cationic derivatives. It is not surprising that other distinguishing features, descriptive or experimental in nature, differ as well for both groups. 

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