A number of metal centres grouped close together which can have direct metal bonding interactions or interactions through a @B00741@, but are not necessarily held together by these interactions.
Source: PAC, 1997, 69, 1251. (Glossary of terms used in bioinorganic chemistry (IUPAC Recommendations 1997)) on page 1265 [Terms] [Paper]
Cite as: IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). Online version (2019-) created by S. J. Chalk. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook.