Ground electronic state description of thiourea coordination in homoleptic Zn2+, Ni2+ and Co2+ complexes using sulfur K‐edge X‐ray absorption spectroscopy

Sulfur K‐edge X‐ray absorption spectroscopy (XAS) was employed to experimentally characterize the coordinative bond between the thiourea (TU) or thiocarbamide ligand and transition metal (TM) ions Zn2+, Co2+ and Ni2+ in distorted tetrahedral and octahedral homoleptic coordination environments. Comparisons of XAS spectra of the free TU ligand and [Zn(TU)4]2+, [Co(TU)4]2+ and [Ni(TU)6]2+ complexes clearly identify spectral features unique to TM2+–S(TU) bonding. Quantitative analysis of pre‐edge intensities describes the covalency of Ni2+—S(TU) and Co2+—S(TU) bonding to be at most 21% and 9% as expressed by the S 3p contributions per TM 3d electron hole. Using relevant Ni2+ complexes with dithiocarbamate and thioether ligands, we evaluated the empirical S 1s → 3p transition dipole integrals developed for S‐donor ligands and their dependence on heteroatom substitutions. With the aid of density functional theory‐based ground electronic state calculations, we found evidence for the need of using a transition dipole that is dependent on the presence of conjugated heteroatom (N) substitution in these S‐donor ligands. Sulfur K‐edge X‐ray absorption spectroscopy in combination with electronic structure calculations defines the ground state bonding in Ni2+ and Co2+ thiourea complexes. For spectral analysis the S 1s → 3p transition dipole integrals were developed and transition metal ion–thiourea bond covalencies determined.