Quanltum chemical calculation of complexes FXOn-CH3CN (X =Cl, Br; n =0-3), which involve monovalent, tervalent, pentvalent and septivalent halogens, have been performed to explore the features of unconventional halogen bonds containing hypervalent halogen.The calculation results reveal that there are two different space arrangements for complexes FXO-CH3CN: an approximately linear structure and a cyclic structure (Fig.).The strength of halogen bonds changes unmonotonously with the increase of halogen atomic oxidation states.Interestingly, frequency vibration analysis shows a red shift of F-X bond and a blue shift of C≡N bond in the complexes FXO-CH3CN(Ⅱ).The natural bond orbital (NBO) analysis indicate that orbital interaction is distinctly different between the Cl complexes and the Br complexes, or between approximate linear structure complexes and cyclic structure complexes.The primary orbital interaction is the BD(3)C=N→BD*(1)F-X in the complexes FXO-CH3CN(Ⅱ), whereas the LP(1)N→ BD*(1)F-X in the other complexes.Furthermore, AIM analysis and energy decomposition calculations are also carried out, which reveal that the electrostatic interaction is the main driven force for the formation of halogen-bonded complexes.