A theoretical investigation of the donor ability of [M(R, R’timd)2] dithiolene complexes towards molecular diiodine (M=Ni, Pd, Pt; R, R’timdt= formally monoreduced disubstituted imidazolidine-2,4,5-trithione)

The sigma-type charge-transfer (CT) interaction between [M(R,R'timdt)2] donors (M = Ni, Pd, Pt; R,R'timdt = formally monoreduced disubstituted imidazolidine-2,4,5-trithione) and diiodine has been thoroughly investigated by a large set of theoretical calculations at different levels of theory (HF, pure and hybrid-DFT with different functionals and basis sets) on I2 (and for the sake of comparison on IBr and Br2), on the model donor dithiolene complexes [M(H2timdt)2], and on the adducts [M(H2timdt)2]·I2 (M = Ni, Pd, Pt). The computations have accounted for the ability of adducts to assume different stoichiometries and to make up polymeric networks based on sulfur−iodine contacts, as in the case of [Ni(Me,iPrtimdt) 2]·I2, which was also characterised by single-crystal Xray diffraction. In addition, the strength of the donor−acceptor interaction has been evaluated through the calculated vibrational features of the model adducts, compared with the experimental FT-Raman spectra recorded on the adducts between [M(Et2timdt)2] and [M(Me,iPr-timdt)2] (M = Ni, Pd, Pt) and diiodine. The frontier-orbital composition, the NBO-charge distribution and bond orders indicate a medium-weak donor ability for the dithiolene donors, which depends only slightly on the nature of the central metal ion, and decreases on passing from M = Ni to M = Pd and Pt, in agreement with the values of the experimental frequencies of the FT-Raman-active I−I stretching vibrations in the adducts [M(Et2timdt)2]·2I2 (M = Ni, Pd, Pt). The ZPE- and CP BSSE-corrected binding energy for [Ni(H2timdt)2]·I2 has been evaluated as −11 kcal/mol.