A Theoretical Study on the Strength and Nature of Metal-dithiolate Bond in Homoleptic Complexes [M(S۲C۲R۲)۲]۲– (M=Ni(II), Pd(II), Pt(II); R=H, Me, CN)

A theoretical study is reported on the strength and nature of metal-ligand bond in some dianionic metal-bis(dithiolate) complexes [ML۲]۲– (M=Ni(II), Pd(II), Pt(II); L= S_۲ C_۲ H_۲^(۲-) (edt۲‒), S_۲ C_۲ Me_۲^(۲-) (dmedt۲‒), S_۲ C_۲ 〖(CN)〗_۲^(۲-) (mnt۲‒)). Firstly, the geometries of all complexes were optimized at the BP۸۶ and M۰۶ levels of theory using the def۲-TZVP basis set. Then the metal−dithiolate and metal(dithiolate)−dithiolate interaction energies, the deformation energies of metal and dithiolate ions as well as the total interaction and stabilization energies of the complexes were calculated and compared. In continuation, an energy decomposition analysis (EDA) was performed to study the nature of metal−bis(dithiloate) bonds in these complexes. The results showed that among the metal complexes studied here, the Pt complexes have the largest values of interaction and stabilization energies. On the other hand, in the case of all three metal ions, the values of total interaction energies and also stabilization energies of [M(edt)۲]۲– and [M(dmedt)۲]۲– complexes are similar or close together and both are larger than those for [M(mnt)۲]۲– complexes. The analysis of metal−(bis)dithiolate bonds showed that the orbital interactions are mainly Ni←Lσ interactions and have considerably less contribution to the total attractive interactions compared to electrostatic interactions.