The structure, properties, and nature of unconventional π halogen bond in the complexes of Al4(2-) and halohydrocarbons.

Quantum chemical calculations have been performed to study the all-metal π halogen bonding in Al(4)(2-)···halohydrocarbon complexes. The result shows the existence of the all-metal π halogen bond in the complexes. There are three interaction modes (top, corner, and side) between Al(4)(2-) and halohydrocarbon. The interaction energy of this interaction varies from a positive value to -90.54 kJ mol(-1) in Al(4)(2-)···I-ethyne-s complex. The interaction strength is affected greatly by the hybridization of C atom and follows the order of C(sp(3)) < C(sp(2)) < C(sp) in most complexes. The methyl group in the halogen donor plays a negative contribution to the formation of halogen bond. The halogen bonding becomes stronger for the heavier halogen atom. The effect of binding site on the strength of halogen bond is related with the nature of halogen atom. The complexes have been analyzed with electrostatic potential, NICS, ELF, NBO, and AIM.