d-electron count, ion-pairing and diagonal twist angles in metallo-bis(dithiolene) complexes

Electronic structure calculations for late transition metals coordinated by two dithiolene ligands are found to be consistent with existing structures and also predict the geometries of Ni(I) species for which no solid state structures have been reported. Of particular interest are the compounds [M(mnt)₂ ]^n- (M = Ni, Pd, and Pt with n = 1, 2, 3; M = Cu with n = 2). Calculations have been performed with and without ion-paring with M(diglyme)⁺ (M = Li, Na, K) and R₄ N⁺ (R = Me, Bu). The diagonal twist angle between two NiS₂ planes is found to depend on (i) the metal's d-electron count, spanning from 0° (planar d⁷ and d⁸ ), to 42° (d⁹ ), to 90° (pseudo-tetrahedral d¹⁰ ), and (ii) the identity of the ion-paired cations. Calculated ion-pairing energies are functions of the cation size and charge-density, being larger for alkali-metal coordinated diglyme and smaller for tetra-alkyl ammonium cations. © 2016 Wiley Periodicals, Inc.