Interplay between non-covalent pnicogen bonds and halogen bonds interactions in ArH2N---PH2FO---BrF nanostructured complexes: a substituent effects investigation

Abstract

The interplay between pnicogen bonds and halogen bonds in nanostructured 4-XPhNH2---PH2FO---BrF (X = H, Me, NH2, N(Me)2, OH, OMe, F, Cl, Br, CHO, CN and NO2) complexes have been investigated using M06-2X/aug-cc-pVDZ quantum chemical calculations. The attraction energy of P---N and O---Br in the nanostructured 4-XPhH2N---PH2FO and PH2FO---BrF dimer systems increased because of the introduction of a third molecule and hence a positive cooperativity is observed during formation of the pnicogen bond and halogen bond in trimer complexes. The effect of substituent exchange on cooperativity between pnicogen bonds and halogen bonds was studied and the results cleared that the cooperativity between pnicogen and halogen bonds increases with an increase in the electron donor capability of substituents. In addition, the obtained values for cooperativity, showed a good correlation with Hammett’s substituent constants. Both the pnicogen and halogen bonds distances in the trimer complexes are dependent on the power of the P---N and O---Br bonds respectively and are shortened compared to the corresponding dimer complex systems. The shortening of both the pnicogen and halogen bond distances in the trimer complexes increases as the electron withdrawing nature of the substituent increases. Natural bond orbital theory is used to investigate how charge redistribution during molecular interactions, leads to the positive cooperative effects. Good correlations between amounts of charge transfer and pnicogen/halogen bond distance variations are obtained. Finally, molecular electrostatic potential and electron density difference maps were used for to increase the depth of understanding. The positive interplay between pnicogen and halogen bonds within the studied complexes is consistent with the results of both the molecular electrostatic potential and electron density difference maps.