Charge-transfer character of halogen bonding: Molecular structures and electronic spectroscopy of carbon tetrabromide and bromoform complexes with organic sigma- and pi-donors

Carbon tetrabromide and bromoform are employed as prototypical electron acceptors to demonstrate the charge-transfer nature of various intermolecular complexes with three different structural types of electron donors represented by (1) halide and pseudohalide anions, (2) aromatic (pi-bonding) hydrocarbons, and (3) aromatics with (n-bonding) oxygen or nitrogen centers. UV-Vis spectroscopy identifies the electronic transition inherent to such [1:1] complexes; and their Mulliken correlation with the donor/acceptor strength verifies the relevant charge-transfer character X-ray crystallography of CBr(4)/HCBr(3) complexes with different types of donors establishes the principal structural features of halogen bonding. (c) 2006 Wiley Periodicals, Inc.