Theoretical study of hydrogen and halogen bond interactions of methylphosphines with hypohalous acids

Ab initio calculations were used to analyze the interactions between hypohalous acids (HOX; X = F, Cl, Br, I) and methylphosphine derivatives (PHnMe3−n, n = 0–3) at the MP2/6-311++G(2d,2p) level of theory. Interaction of HOX with PHnMe3−n lead to both hydrogen bond (HOXPHnMe3−n–HB) as well as halogen bond (HOXPHnMe3−n–XB) complexes. Stabilities of both HB and XB complexes increase with basicity of the phosphines that is larger for XB complexes. However HB complexes of a phosphine molecule with different HOX are in the same order of stabilities, but XB complexes of heavier hypohalous acids are more stable. Except for HOCl–PH3, HOCl–PH2Me and HOCl–PHMe2 systems, XB complexes have greater stabilities than their HB counterparts in other cases. Electron densities of complexes were characterized with the atoms-in-molecules (AIMs) methodology. The charge transfer within dimers was analyzed by means of natural bond orbitals (NBOs).