Ab initio study on the resonance effect in the hydrogen- and halogen-bonded complexes of hypohalous acids with formamide and its derivatives

► Two-way effects exist in the halogen bond complexes of formamide and its derivatives with hypohalous acids. ► The hydrogen bonded complexes FAX-HA(R) are favored. ► The strength of halogen bond in FAX-R is close to that of HA hydrogen bond as the size of the R atom increases. ► The nature of the halogen atom R has relatively little impact on the strength of the hydrogen bond.