Tuning Supramolecular Architecture via Chalcogen Selection: Enhanced Covalency of IIII···SeCN over IIII···SCN Drives the Switch from 4- to 8-Atomic Motifs

Abstract

This work presents the first systematic study of halogen bonding interactions between iodine(III) centers of diaryliodonium cations and selenocyanate (SeCN–) anions─a previously undocumented type of IIII···Se contact. A series of diaryliodonium selenocyanates was synthesized via anion metathesis and characterized by single-crystal X-ray diffraction; DFT calculations were employed to analyze the nature of noncovalent interactions. Crystallographic analysis revealed short I···Se (3.22–3.30 Å, Nc 0.83-0.85) and I···N (2.82–2.96 Å, Nc 0.80-0.84) contacts forming heterotetrameric and heterooctameric assemblies. Comparison with the structurally analogous thiocyanate systems uncovered a remarkable architectural switch: while iodonium thiocyanates preferentially form 4-atomic cycles via I···N interactions, the selenocyanate analogues adopt 8-atomic heterotetrameric arrangements involving I···Se contacts. Computational analysis demonstrates that this switch is driven by the enhanced covalent character of IIII···Se versus IIII···S halogen bonds, as evidenced by larger Wiberg bond indices (0.16–0.20 vs 0.13–0.16 for I···S). The larger covalent contribution and charge transfer capability in I···Se bonds (BSSE energies −21 to −25 kcal/mol vs ∼ – 13 kcal/mol for the I···N interaction in the same selenocyanate systems) create a stronger energetic preference for I···Se bonding compared to the more balanced competition between I···S and I···N in thiocyanates. These findings establish chalcogen selection as a tool for tuning supramolecular architectures, identify SeCN– as an effective halogen bond acceptor, and expand the library of Se-based acceptors available for iodine(III) sites.