Categorization of Metalloboranes using Skeletal Numbers

Abstract

Metalloboranes have been analyzed and categorized using skeletal numbers. Skeletal numbers are extremely helpful in categorizing chemical clusters literally ranging from a single to an infinite number of skeletal elements of the main group and transition metals. The method involves decomposing a cluster formula comprising of a number of skeletal elements using skeletal numbers into a single whole number (K). Knowing the number of skeletal elements in a cluster (n), the K(n) parameter is obtained. The type of series S=4n+q is readily derived from the K(n) parameter. This is followed by the derivation of the capping parameter, Kp=C y C[Mx] and the categorization parameter K*=C y +D z where y+z=n, the number of skeletal elements in the cluster. The cluster valence electrons can be calculated from the relationship VE=12y+14z+2 for transition metal clusters or VE=2y+4z+2 for main group elements or VE=2y+4z+2+10m where m=the number of transition metal elements present when a cluster has a mixture of elements from the main group and transition metals. The categorization parameter can also act as a guide to predict a possible symmetry of a cluster and to construct an isomeric skeletal shape of a cluster. This approach was used to categorize more than 20 metalloborane clusters as well as a few non-metalloborane clusters for comparison purposes. The isomeric skeletal structures so constructed obey the 8 or 18 electron rule as defined by coordination theory.