Molecules or ions that contain too few electrons to allow their bonding to be described
exclusively in terms of two-center, two-electron, i.e.,
covalent, bonds. Such molecules or certain fragments in these are often held together
by the multicenter bonds.
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. https://doi.org/10.1351/goldbook