Vibrations of the Interstitial Atoms in Transition Metal Clusters

Abstract

The interstitial metal clusters form a fascinating class of complexes of the transition metals, where a non-metallic atom X is uniquely bonded to the metal atoms of the core. From the structural point of view, two subclasses might be distinguished, the properly called “interstitial” clusters, where the heteroatom is completely surrounded by the metal atoms of the cage in which it is inserted, and the “semi-interstitial” or “exposed” clusters, where the heteroatom is placed on, or nearby, a face or an edge of a metal polihedron. Moreover, even if the carbon atom remains the first reported and the most commonly encountered heteroatom, one example at least has appeared with hydrogen¹, nitrogen,² boron,³ phosphorous,⁴ sulphur,⁵ silicium,⁶ arsenic⁷ and antimony⁸ interstitial atoms. Together with these more common systems, there is an increasing number of policarbido and polihydrido complexes, containing several interstitial heteroatoms⁹; recently, an example of a cluster with carbon and hydrogen together was reported.¹⁰ Furthermore, some dicarbido clusters have a C₂ unit, with the two carbon atoms bonded to each other, in both interstitial₁₁ and exposed₁₂ configurations. Some selected examples of the core structures of interstitial (Fig. l),exposed (Fig. 2) and polihetero- atom (Fig. 3) metal clusters are illustrated.

Key Words:

• carbido
• hydrido
• interstitial
• metal cluster
• nitrido
• vibrational spectroscopy