Stabilization of metal clusters for catalysis

A major problem in defining cluster catalysis has been to prove that catalysis does not occur after either fragmentation to mononuclear complexes, followed by 

A potential problem with these stabilizing bridging ligands is that they are often bulky and some catalytic reactions are then blocked because larger reagents cannot find access to the metal centers. An elegant solution is to use an interstitial atom which can bind to six or more transition metal atoms. This is an important component of Section 2.11, in which clusters containing interstitial carbide are used as examples. 

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