The nature of π-hole spodium bonds in the HgLCl2(L = pyrrole, pyrazole, imidazole, pyridine, pyridazine, and pyrimidine) complexes: from noncovalent to covalent interactions

Abstract

The nature of π-hole spodium bonds in the HgLCl₂⋯ZH₃/CH₂Y complexes (L = pyrrole 1, pyrazole 2, imidazole 3, pyridine 4, pyridazine 5, and pyrimidine 6; Z = N, P, As, and Sb; Y = O, S, Se, and Te) has been studied using theoretical calculations. The electrophilicity of the π-hole in the tri-coordinated Hg^II complexes varies with the type of N-heterocyclic ligand. The strength and nature of the π-hole spodium bond is closely related to the properties of the Lewis bases. In the case of HgLCl₂⋯ZH₃, the strength of the π-hole spodium bond weakens as the nucleophilicity of the base decreases, following the sequence HgLCl₂⋯NH₃ > HgLCl₂⋯PH₃ > HgLCl₂⋯AsH₃ > HgLCl₂⋯SbH₃. The Hg⋯Z spodium bonds change from a partially covalent interaction to a close-shelled noncovalent interaction. The nucleophilic ability of CH₂Y decreases in the order CH₂O > CH₂S > CH₂Se > CH₂Te, while the strength of the π-hole spodium bond follows the order HgLCl₂⋯OCH₂ < HgLCl₂⋯SCH₂ < HgLCl₂⋯SeCH₂ < HgLCl₂⋯TeCH₂. The Hg⋯Y spodium bond undergoes a transition from a close-shelled noncovalent to a partially covalent interaction, resulting in an incremental increase in the degree of covalence. The Hg⋯Te spodium bond exhibits certain characteristics resembling those of a coordinate covalent bond. The inter-orbital interactions observed in the formation of the HgLCl₂⋯YCH₂ complexes appear to be significantly stronger compared to those observed in the HgLCl₂⋯ZH₃ complexation.