Aromaticity of Ni bis-dithiolenes complexes

The Ni bis-dithiolene complexes with D2h symmetry were predicted to be stable at B3LYP/6-311++G(d) level. The analyses of nature bond orbital and nucleus-independent chemical shift (NICS) at B3LYP/6-31G(d) and GIAO-B3LYP/6-31G(d) level revealed the aromatic character of the Ni bis-dithiolene complexes. The total isotropic NICS (NICSiso) at the ring center [NICS(0)iso] has main contribution from the molecular orbitals (MOs) within the molecular plane according to the analysis of canonical MO (CMO) contributions to NICS. The π MOs have large contribution to the NICSiso at 1 Å above the ring center [NICS(1)iso]. Both analyses of CMO and nature local MO (NLMO) predict that the Ni-S σ bonds weaken the aromaticity of the Ni(S2C2H2) and Ni(bdt)2 complexes. The three d atomic orbitals with lone pair electrons of the Ni atom and the delocalized π bond among S-C-C-S have large contribution to the NICS(0)iso and NICS(1)iso in Ni(S2C2H2) and Ni(bdt)2 according to the analyses of NLMO. The C-C π bond has large contribution to the NICS(n)iso (n = 0 or 1) in Ni(S2C2H2)2, while the delocalized S-C π bond has large contribution to the NICS(n)iso (n = 0 or 1) in Ni(bdt)2.