Methylenecyclopropane-boron trifluoride van der Waals complexes; an infrared and DFT study

The formation of weakly bound molecular complexes between methylenecyclopro pane (MeCP) and BF3 dissolved in liquid argon has been investigated using F TIR spectroscopy. Experimental evidence was found for the formation of a 1: 1 complex in which the BF, moiety binds to the exocyclic C=C double bond, w hereas at higher concentrations of BF3, weak absorption bands due to MeCP ( BF3)(2) were also observed. Using spectra recorded at different temperature s between 105 and 129 K, the complexation enthalpy for the 1:1 complex in l iquid argon was determined to be -10.7(3) kJ mol(-1). Structural and spectr al information on the complexes was obtained from density functional calcul ations at the B3LYP/6-311++G(d,p) level. Applying Free Energy Perturbation Monte Carlo calculations to account for the solvent influences and statisti cal thermodynamics to calculate the zero-point vibrational and thermal infl uences, the complexation energy for the 1:1 complex was estimated, from the experimental complexation enthalpy, to be -16.0(10)kJ mol(-1). This value is compared with the B3LYP/6-311++G(d,p) complexation energies and with sin gle point energies calculated at the MP2 = full/aug-cc-PVTZ level.