The C–Cl⋯N halogen bond, the weaker relative of the C–I and C–Br⋯N halogen bonds, finally characterized in solution

Abstract

The formation of halogen bonded complexes between trimethylamine (TMA) and the trifluoro halomethanes CF 3I, CF 3Br and CF 3Cl dissolved in liquid xenon, krypton and argon, respectively, has been investigated using FTIR spectroscopy. For all Lewis acids, evidence was found for the formation of C–X⋯N halogen bonded 1:1 complexes. This study provides the first experimental characterization of a complex formed under thermodynamic equilibrium conditions in solution via a C–Cl⋯N halogen bond. Using spectra recorded at different temperatures, the complexation enthalpies for the complexes were determined to be −28.7(1) kJ mol −1 (CF 3I ·TMA), −18.3(1) kJ mol −1 (CF 3Br ·TMA) and −8.9(2) kJ mol −1 (CF 3Cl ·TMA). The results from the cryospectroscopic study are compared with ab initio calculations at the MP2/6-311++G(d,p) + LanL2DZ∗ level.