In this work, the interactions between the fragments in homoleptic square-planar d8 metal bis(1,2- dichalcogenolate) complexes [M(E2C2(CN)2)2]2– (E = S, Se, Te; M=Ni(II), Pd(II), Pt(II)) have been investigated by using density functional theory (BP86, M06) calculations with a focus on the nature of metal dichalcogenolate bonds. Four types of interaction energies between the fragments, the deformation energies of metal and dichalcogenolate ions as well as the total interaction and stabilization energies of the complexes were calculated and compared. An energy decomposition analysis (EDA) was also performed to study the nature of metal bis(dichalcogenolate) bonds in these complexes. The results showed that the stabilization and total interaction energies are decreased by changing the chalcogen atom from sulfur to selenium and from selenium to tellurium ([M(S2C2(CN)2)2]2– > [M(Se2C2(CN)2)2]2– > [M(Te2C2(CN)2)2]2–). The analysis of metal bis(dichalcogenolate) bonds showed that the orbital interactions are mainly Metal←Lσ and have considerably less contribution to the total attractive interactions compared to electrostatic interactions. However, the contribution of orbital interactions, in an opposite trend with the interaction energies, is increased by changing the chalcogen atom from sulfur to selenium and from selenium to tellurium.
