A number of metal centres grouped close together which can have
direct metal bonding interactions or interactions through a bridging ligand
, but are not necessarily held together by these interactions.
PAC, 1997, 69, 1251
(Glossary of terms used in bioinorganic chemistry (IUPAC Recommendations 1997))
on page 1265
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook