Bonding and Reactivity of Metal Clusters

This paper consists of two parts. In the first, the simple concept of bond order is used to study the different types of metal-metal bonds found in a wide range of metal clusters. These bond orders are determined with two simple methods: electron counting and elementary molecular orbital theory. Emphasis is placed on a number of recently prepared dichromium complexes with bond orders larger than 4 and exceedingly short bond lengths. In the second part, we outline the results of some very recent reactivity studies of the aforementioned dichromium and related complexes. It is found that quintuply bonded dichromium and dimolybdenum clusters can undergo some well known processes such as insertion, oxidation, small molecule activation, cycloaddition, etc. However, there are also instances where the quintuple MM bond in these clusters is completely disrupted in one single step. It is evident that these results will open up an exciting area of research in coordination and cluster chemistry.