文摘
This article provides a means to classify and represent compounds that feature 3-center 2-electron (3c–2e) interactions according to whether (1) the two electrons are provided by one or by two atoms; (2) the central bridging atom provides two, one, or zero electrons; and (3) the interaction is open or closed. Class I 3c–2e bonds are defined as those in which two atoms each contribute one electron to the 3-center orbital, while Class II 3c–2e bonds are defined as systems in which the pair of electrons are provided by a single atom. The use of appropriate structure-bonding representations enables the [ML l X x Z z ] covalent bond classification of the element of interest to be evaluated. This approach is of considerable benefit in predicting metal–metal bond orders that are in accord with theory for dimetallic compounds that feature bridging hydride and carbonyl ligands.