DFT studies on some properties of maleonitriledithiolate complexes [M(mnt) ₂] ^2- (M = Ni, Pd, Pt and Zn, Cd, Hg)

The structures and some molecular properties of the complexes M(mnt) ₂ ^2- (M = Ni, Pd, Pt and Zn, Cd, Hg; mnt ^2- = deprotonated maleonitriledithiolate) have been studied by using density functional theory (DFT) B3LYP/LanL2DZ level of theory. Computed binding energies show that the sequences of binding strengths are Ni < Pd < Pt and Cd < Hg < Zn. The natural bonding orbitals analyses show that Ni, Pd and Pt gain 1.40e, 1.62e and 1.72e, respectively to their ns, (n-1)d _{x2- y2} and (n-1)d _z2 orbitals from both ligand mnt ^2- and (n - 1)d _yz of metal ions, while Zn, Cd and Hg complexes gain electrons to their ns orbitals. The absorption spectra of these complexes were obtained by using time-dependent density functional theory associated with polarized continuum model. Comparison of the absorption spectra in acetonitrile solution with those in gas phase show that the solvatochromic effect made the lowest energy absorption red shift by 31, 34 and 44 nm for d ⁸ metal complexes Ni(mnt) ₂ ^2-, Pd(mnt) ₂ ^2- and Pt(mnt) ₂ ^2-, respectively, while blue shift by 28, 44, 25 nm for d ¹⁰ metal complexes Zn(mnt) ₂ ^2-, Cd(mnt) ₂ ^2- and Hg(mnt) ₂ ^2-, respectively. The calculated results reproduced the experimental data with the deviations less than 5% for Ni-S stretching vibrational frequencies and less than 3% for other vibrational modes.