Comparative solid state and solution NMR structural and dynamic studies on tetra- and higher-nuclearity transition metal carbonyl clusters

Abstract

Clusters provide interesting models for surfaces and sometimes provide a controlled step-wise sequence of cluster growth. Although the metal geometry in homometallic clusters can now be predicted reliably from electron counting rules, it is much more difficult to predict both the metal site occupancy in heterometallic clusters and the carbonyl and non-carbonyl ligand site occupancies on the metallic framework; this is especially true for the ubiquitous hydrogen and structural elucidation of these clusters has had to rely heavily on neutron diffraction and NMR measurements, which are particularly useful when the metal has a spin. Similarly, the ease of migration and the exact migrational pathway(s) of CO and/or H are also difficult to predict, although NMR measurements in solution often allow the detailed pathway of ligand migrations to be unambiguously established. The purpose of this Perspective is to compare and contrast the dynamic and structural information available from solid state multinuclear NMR measurements with data obtained from solution NMR and other related spectroscopic and structural measurements on tetra- and higher-nuclearity transition metal carbonyl clusters.