We investigate the equatorial ligand effects on the diradical character (y) dependence of the longitudinal second hyperpolarizability (gamma) of the Re(IV)(2)F-8 transition-metal dinuclear complex with different bond lengths using the spin-unrestricted coupled-cluster method. It is found that the equatorial ligands do not affect the intrinsic y-gamma relationship nor the d sigma-electron dominant contribution to the maximum gamma (gamma(max)) observed in the bare dinuclear analogs but gamma(max) of Re(IV)(2)F-8 is about one order of magnitude larger than that of Re(IV)(2). (C) 2013 Elsevier B.V. All rights reserved.