Assessment of several DFT functionals in calculation of the reduction potentials for Ni-, Pd-, and Pt-bis-ethylene-1,2-dithiolene and -diselenolene complexes.

We performed an assessment of 10 common DFT functionals to determine their suitability for calculating the reduction potentials of the ([M(S2C2H2)2](0)/[M(S2C2H2)2](1-)), ([M(Se2C2H2)2](0)/[M(Se2C2H2)2](1-)), ([M(S2C2H2)2](1-)/[M(S2C2H2)2](2-)), and ([M(Se2C2H2)2](1-)/[M(Se2C2H2)2](2-)) redox couples (M = Ni, Pd, and Pt). Overall it was found that the M06 functional leads to the best agreement with the gold standard CCSD(T) method with an average difference of only +0.07 V and a RMS of 0.07 V in calculated reduction potentials. The variability in calculated reduction potentials between the various DFT functionals arise, in part, from the multireference character of these systems, which was determined by the T1 diagnostic values. Thus, the bisdiselenolene complexes show similar multireference character as the bisdithiolene complexes, which were previously shown to have such character. In particular, for the Ni-, Pd-, and Pt-bisdiselenolene complexes the average T1 values are 0.05, 0.03, and 0.02, respectively. For the CCSD(T) calculations the similarities in the reduction potentials between analogous bisdithiolene and bisdiselenolene redox couples, which appear to be independent of the metal, is a result of the noninnocence of the dithiolene and diselenolene ligands. Thus, the reduction potential is more dependent on the ligand than the metal.