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Various recently introduced multicenter bond indices were reviewed and their interrelations discussed. In addition to this analysis a simple three-center three-orbital model of three-center bonding was proposed and applied to several molecules with three-center bonds. The applicability of this model was tested by comparing with semiempirically and ab-initio calculated bond indices. It was shown that the simple model correctly describes the phenomenon of three-center bonding. Another interesting and useful application of this model concerns the interpretation of the indices as an indicator of the number of electrons involved in three-center bonding (3c-2e vs 3c-4e bonds).
Ponec et al. (Sat,) studied this question.