The four-coordinate, S-ligated, nickel(II) complexes can manifest both S=1 and S=0 ground states in tetrahedral and tetragonal geometries, respectively. We present a combined experimental and theoretical investigation into the interconnectedness of the nature of the S ligand, coordination geometry, and spin state. We extend the literature data of nickel(II) thiolate and dithiolene complexes with two tetragonal nickel(II) complexes containing bis(norbornanedithiolate) and tetrathiacyclotetradecane ligands. After developing transition dipole integrals for the dithiolate and the thioether sulfur absorbers, sulfur K-edge data suggest that the Ni-S bond is highly covalent for the two new tetragonal complexes, similarly to the nickel(II) bis(dithiolene) complex. This suggests a non-innocent coordination chemistry and an inverted Ni-S bonding. Notably, the high Ni-S bond covalency could not be reproduced with the popular GGA, meta-GGA, or hybrid density functionals. We found that the LB94 functional is needed to approach the experimental electronic structure of the tetragonal, formally nickel(II) sulfur coordination compounds in agreement with high level, ab initio MO theory calculations.

Age of non-innocence for nickel coordination complexes

243rd National Meeting (2012)

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