QUALITATIVE MODELS FOR THE NMR CHEMICAL-SHIFTS OF INTERSTITIAL ATOMS IN CLUSTERS

Qualitative models for the NMR chemical shifts of interstitial atoms in clusters are presented which draw heavily upon our present understanding of cluster bonding. The deshielding of interstitial hydrogen atoms can be understood in terms of secondary paramagnetic fields arising on the transition metal centres, whilst that of interstitial carbon and nitrogen atoms is thought to arise from more local sources. In these models, Stone's Tensor Surface Harmonic theory is used to describe the interaction between the interstitial atoms and the metal cluster framework. Model calculations of the susceptibility tensor for [Ru6H(CO)18]- and the electronic structures of [Rh6C(CO)15]2- and [Rh6N(CO)15]- support the proposals.