Dual Donor–Acceptor Behavior of Tellurium(II) in Cocrystals: Tuning Noncovalent Interactions with σ- and π-Hole Donors

Abstract The unique electronic structure of tellurium enables a dual donor–acceptor behavior in noncovalent interactions (NCIs) that can be systematically tuned. In this work, we investigate the cocrystallization of tellurium(II) bis(diethyldithiocarbamate) (1) with σ-hole (1,4-diiodo-2,3,5,6-tetrafluorobenzene and 1,3,5-triiodo-2,4,6-trifluorobenzene) and π-hole (1,2,4,5-tetracyanobenzene, TCB) donors. Single-crystal X-ray diffraction reveals that σ-hole donors interact with the electron-rich p-belt of the TeII center, which serves as a halogen bond (HaB) acceptor through directional I···Te contacts. This engagement establishes a competitive regime that weakens or fully suppresses the intrinsic intermolecular Te···S chalcogen bonds (ChB). Conversely, the π-hole donor TCB approaches the {TeS4} moiety face-on, allowing for cooperative interactions that preserve the ChB network. Theoretical studies (MEP, QTAIM, NCIplot, EDA, and NBO) corroborate these findings, revealing that the spatial segregation of σ-holes (positive MEP) and the p-belt (negative MEP) on the Te atom allows it to act simultaneously as a Lewis acid and a Lewis base. NBO analysis quantifies the charge transfer, identifying strong LP(Te or S) → σ*(C–I) HaB and dominant LP(S) → σ*(Te–S) ChB contributions.