Chalcogen Bonding\nbetween Tellurium(II) and the Isocyanide\nCarbon

A novel type of chalcogen bond between tellurium(II)\nand the carbon\natom of the isocyanide groups has been discovered in five cocrystals: <b>1</b>·TePy<sup>F</sup><sub>2</sub> (two polymorphs), <b>2</b>·TePy<sup>F</sup><sub>2</sub>, <b>3</b>·2TeTol<sup>F</sup><sub>2</sub>, and <b>3</b>·TePy<sup>F</sup><sub>2</sub>. These were obtained by cocrystallization of monoisocyanide\ncompounds CN-Np (Np-1 is 1-naphthyl; <b>1</b>) and CNC<sub>6</sub>H<sub>4</sub>CCPh (<b>2</b>) and the <i>bis</i>-isocyanide\n1,4-(CN)<sub>2</sub>C<sub>6</sub>Me<sub>4</sub> (<b>3</b>) with\nthe chalcolanes TePy<sup>F</sup><sub>2</sub> and TeTol<sup>F</sup><sub>2</sub> (Py<sup>F</sup> = 4-NC<sub>5</sub>F<sub>4</sub>, Tol<sup>F</sup> = 4-CF<sub>3</sub>C<sub>6</sub>F<sub>4</sub>). The structures\nwere studied by X-ray diffraction, revealing Te···C\ndistances of 2.9–3.2 Å (77–85% of Bondi vdW sum)\nand also characterized by ATR FTIR spectroscopy. Computational analysis,\nincluding density functional theory (DFT) calculations, energy decomposition\nanalysis (EDA), molecular electrostatic potential (MEP), quantum theory\nof atoms in molecules (QTAIM), noncovalent interaction (NCI) plot,\nand natural bond orbital (NBO) analysis, showed that these chalcogen\nbonds are primarily electrostatic but with relatively significant\norbital contributions. Monofunctional acceptors (<b>1</b> and <b>2</b>) form di- and oligomers, while the bifunctional acceptor\n(<b>3</b>) creates extended supramolecular structures. Interaction\nstrengths range from −6.4 to −9.6 kcal/mol for Te···CN\ncontacts.