Substituent-Driven Switch Between Os…O and O…H Interaction and the Emerging Cooperative/Anti-Cooperative Effect in...

In this study, we present a quantum mechanical investigation of Osme-bonded binary and ternary complexes formed between OsO₄, substituted pyridines (X-Py; X = NH₂, OCH₃, OH, CH₃, F, Cl, CF₃, CN, and NO₂), and H₂O molecule, highlighting their potential relevance for higher-order cocrystal design without relying predominantly on hydrogen bond. The binding energies of Os…N Osme-bonded binary complexes (-39.1 to -26.5 kJ/mol) exhibit pronounced substituent dependence and correlate strongly with descriptors like proton affinity, ionization potential, and V_s,min. Atoms in molecule (AIM) analyses confirm partial covalent character of Os…N bond, stabilized by charge transfer and hyperconjugation effects. Incorporation of H₂O results in structurally distinct ternary motifs, whose cooperative or anti-cooperative nature can be selectively tuned through rational pyridine substitution. Unsubstituted pyridine forms two ternary arrangements (type I and type II), whereas substitution markedly alters the stability and existence of these motifs, particularly for type II complexes. For type II complexes, electron-donating groups promote hydrogen bonding and reinforce Os…N interactions, resulting in pronounced cooperativity, while electron-withdrawing groups favor alternative Os…O pathways and induce anti-cooperativity. Overall, this study shows how substituent-induced OsO₄ distortion controls σ-hole accessibility, directing Osme versus hydrogen bonding to tune structure, cooperativity, and stability in multicomponent assemblies.