Do nitrogen bases form chlorine-shared and ion-pair halogen bonds?

Ab initio calculations have been carried out to investigate the structures, binding energies, and spin-spin coupling constants of complexes with FCl as the Lewis acid and a series of sp, sp(2), and sp(3) hybridized nitrogen bases. These properties indicate that neutral complexes are stabilized by traditional F-Cl center dot center dot center dot N halogen bonds, although the chlorine-shared character of the bond is greater with sp2 and sp3 bases. Thus, these complexes are dramatically different from neutral complexes FCl:CNX with sp hybridized carbon bases, which exhibit traditional, chlorine-shared, and ion-pair halogen bonds. (C) 2011 Elsevier B. V. All rights reserved.