Probing the nature of intramolecular (sp3)C–H⋯Cu(i) interactions in organo thione copper(i) cages

Abstract

The assessment of copper(I) and hydrogen interactions is challenging and should be approached with caution. In this paper, we report an assessment of multiple copper(I) and hydrogen interactions in two unique copper(I) thione cages. Copper(I) N-heterocyclic thione cages [{Cu₂(μ²-Br)₂(μ²-L¹)}₂] (1) and [{Cu₂(μ²-I)₂(μ²-L¹)}₂] (2) were synthesized and characterized with proximity enforced Cu⋯H interactions. Cages 1 and 2 were tetranuclear copper(I) cages constituting Cu(I) dinuclear cores bridged by the N-heterocyclic thione ligand. The Cu(I) adopted a distorted tetrahedral geometry. The structures of 1 and 2 featured proximity-enforced intramolecular Cu⋯H–C interactions between (sp³)C–H of the methylene moiety and Cu(I). Density functional theory (DFT) calculations were carried out to understand the bonding nature of 2. The optimized structural parameters were comparable to those of the solid-state structures. Natural bond orbital (NBO) analysis gave insights into the donor–acceptor orbitals involved between (sp³)C–H and Cu(I). The σ*_C–H orbital was found to overlap with the Cu-filled d orbital. Notably, the theoretical and experimental studies suggest that the Cu⋯H interactions found in 1 and 2 are three-center–four-electron (3c–4e) anagostic bonds.