ClEe as the halogen bond acceptor: studies on strong halogen bonds

The ClEe anion as the halogen bond acceptor, the diiodotetrafluoroethane I(CF2)(2)I and its derivatives I(MF2)(n)I (M = C, Si, Ge, Sn) as the halogen bond donor, and the strong halogen bonds could be formed. The halogen bonds between I(MF2)(n)I and ClEe have been designed and investigated by Moller-Plesset perturbation/aug-cc-pVDZ calculations together with the aug-cc-pVDZ-pp basis set for iodine and stannum. The halogen bonds in the I(MF2)(n)Ia (TM) a (TM) a (TM) ClEe complexes are strong, which are apparently related to the group IV elements, becoming stronger along the sequence of M = Si, C, Ge, Sn. Accompanied with increasing number (n) of MF2 unit, the halogen bonds (M = Si, Ge, Sn) also become stronger. The energy decomposition analyses reveal that the exchange energy contributes most in forming these halogen-bonded interactions. In the meantime, the electrostatic energy is also a significant factor for the Ia (TM) a (TM) a (TM) ClEe interactions. The halogen bonds of I(MF2)nIa (TM) a (TM) a (TM) ClEe(M = C, Ge, Sn) belong to partial-covalent interactions, while they are noncovalent interactions when M = Si.