Quantitative assessment of the nature and strength of Au‒dithiolate bond in gold(III) bis(1,2-dithiolate) homoleptic complexes

Quantum chemical calculations at the BP86/def2-TZVP and M06/def2-TZVP levels of theory have been carried out to investigate the nature and strength of the Au-dithiolate bond in gold(III) bis(1,2-dithiolate) homoleptic complexes [AuL₂]^– where L represents various ligands: ethylene-1,2-dithiolate (edt²⁻), 1,2-bis(methyl)ethylenedithiolate (dmedt²⁻), 1,2-maleonitrile-1,2-dithiolate (mnt²⁻), benzene-1,2- dithiolate (bdt²⁻), 4,5-dimethylbenzene-1,2-dithiolate (dmbdt²⁻), and 4,5-dicyanobenzene-1,2-dithiolate (dcbdt²⁻). The study involved calculating the interaction energies between the fragments as well as assessing the deformation energies of both the Au³⁺ ion and the dithiolate ions. Furthermore, the total interaction energy and the stabilization energy of the complexes were determined and compared. The investigation also included conducting an energy decomposition analysis (EDA) to examine the characteristics of the bonds between Au(III) and bis(dithiolate) in these complexes. The results demonstrated that the complexes containing dithiolates with ‒CN substitutions ([Au(mnt)₂]^– and [Au(dcbdt)₂]^–) have smaller values of stabilization and interaction energies compared to other ones. The analysis of Au − (bis)dithiolate bonds revealed that the electrostatic interactions make a more substantial contribution to the total attractive interactions compared to the orbital interactions. Indeed, the dominant role in stabilizing the complexes is played by the electrostatic attractions between the Au³⁺ and the dithiolate ligands. Moreover, both the Au → Lπ and Au → Lσ backdonations in all studied complexes are very weak.

Graphical abstract