Unveiling σ- and π-hole interactions in COSe-XCN (X = F, Cl, Br, and I): Theoretical insights into halogen substitution effects

XCN molecules (X = F, Cl, Br, I) are linear pseudohalogen species containing a reactive and toxic cyanide group. Their high electrophilicity and toxicity limit experimental studies. Therefore, this work employs ab initio theoretical methods to investigate their interactions with COSe. Our calculations reveal that the interaction between XCN and COSe leads to the formation of three distinct linear complexes, stabilized via halogen bonding (O⋯X), tetrel bonding (N⋯C), and chalcogen bonding (N⋯Se), denoted as S A , S B , and S C , respectively. Among these, the S C -structure complexes exhibit the highest stability, followed by S A and S B . The interaction energies ( ΔE 0 ) range from −0.48 to −2.50 kcal·mol −1 , following the stability order S C (−2.05 to −2.50) > S A (−0.48 to −2.30) > S B (−1.13 to −1.37). Energy decomposition analysis (EDA) reveals that electrostatic interactions dominate in the S A and S C complexes (≈48–57 %), whereas dispersion contributions prevail in the S B complexes (≈49 %), highlighting distinct bonding mechanisms for each type. These energetic and electronic characteristics, further supported by NBO (Natural Bond Orbital), QTAIM (Quantum Theory of Atoms in Molecules), and NCI (Noncovalent Interaction Index) analyses, confirm the critical role of σ-hole and π-hole features in stabilizing the noncovalent assemblies. • Ab initio study reveals three linear COSe···XCN complexes via XB, TB, and ChB. • Stability order: S C > S A > S B ; energies range from −0.48 to −2.50 kcal/mol. • EDA shows electrostatic dominance in S A /S C (48–57 %), dispersion in S B (49 %). • NBO, QTAIM, NCI confirm σ/π-hole roles in stabilizing assemblies.