The delta bond—an old story with a new twist

Abstract

The nature of the two electron δ-bond is examined in detail, with attention to the four states that constitute the δ-manifold, viz., 1A1g (ground state), 3A 2u, 1A2u and lA1g*, in a species, M2X8n-, with D4h symmetry. The effects of increasing the M-M distance, twisting from D4h through D4 to D4d, and configuration interaction are then discussed. Experimental measurements of the 1A1g - 3A2u separations in mo2C14(P-P)2 complexes with twist angles between 17 and 40° as well as CASSCF calculations for the model system. mo2C14,(PH3)4, are discussed. It is concluded that the δ-bond energy is 12 (Exp.) - 17 (theor.) kcal mol-1 and the rotational barrier is 24.5 kcal mol-1. © 1992 Walter de Gruyter