An insight into the nature of the interaction between mesoporous solids and carbonyl clusters has been obtained from new solid-state NMR spectroscopic data. A series of simple clusters have been synthesised and deposited on the mesoporous material MCM-41. Results form 2 9 Si{ 1 H} solid-state NMR on both the pure and deposited species and 5 9 Co NMR give rise to information about the nature of the cluster and its binding in the channels of the mesoporous material. Analysis of 2 9 Si{ 1 H} variable contact time experiments shows a significant increase in the rate of cross polarisation, particularly for the Q 4 sites, once MCM-41 is deposited with a carbonyl cluster. 5 9 Co NMR shows that the Co(CO) 4 - cluster retains its original geometry when deposited in MCM-41.