Chalcogen Bonding between Tellurium(II) and the Isocyanide Carbon

A novel type of chalcogen bond between tellurium­(II) and the carbon atom of the isocyanide groups has been discovered in five cocrystals: 1·TePyF 2 (two polymorphs), 2·TePyF 2, 3·2TeTolF 2, and 3·TePyF 2. These were obtained by cocrystallization of monoisocyanide compounds CN-Np (Np-1 is 1-naphthyl; 1) and CNC6H4CCPh (2) and the bis-isocyanide 1,4-(CN)2C6Me4 (3) with the chalcolanes TePyF 2 and TeTolF 2 (PyF = 4-NC5F4, TolF = 4-CF3C6F4). The structures were studied by X-ray diffraction, revealing Te···C distances of 2.9–3.2 Å (77–85% of Bondi vdW sum) and also characterized by ATR FTIR spectroscopy. Computational analysis, including density functional theory (DFT) calculations, energy decomposition analysis (EDA), molecular electrostatic potential (MEP), quantum theory of atoms in molecules (QTAIM), noncovalent interaction (NCI) plot, and natural bond orbital (NBO) analysis, showed that these chalcogen bonds are primarily electrostatic but with relatively significant orbital contributions. Monofunctional acceptors (1 and 2) form di- and oligomers, while the bifunctional acceptor (3) creates extended supramolecular structures. Interaction strengths range from −6.4 to −9.6 kcal/mol for Te···CN contacts.