Tetracarbon Metallocarboranes. 6. Stereochemical Relationships Between Co2C4B6Cage Isomers Formed by Oxidative Fusion. Crystal Structure of (n5-C5H5)2Co2(CH3)4C4B6H6' Isomer V.

摘要

Structural studies of carboranes and metallocarboranes having four carbon atoms in the same polyhedron are proving to be an effective probe of the relationship between electron population and cage geometry, and have revealed a number of unprecedented molecular shapes. Since the formal replacement of a BH by a CH (or C-alkyl) group in a closed polyhedral (closo) system increases the number of valence electrons in the cage skeleton, one can predict from electron-counting arguments that tetracarbon carboranes will exhibit cage structures that are more open than their dicarbon counterparts; simply put, this is a consequence of the fact that the additional electrons in most cases must occupy antibonding orbitals, thereby producing some sort of cage-opening or distortion. (Author)