On the HCl and DCl complexes of methylenecyclopropane in liquid argon

The formation of weak molecular complexes between methylenecyclopropane (Me CP) and HCl or DCl dissolved in liquid argon and liquid nitrogen has been i nvestigated using infrared spectroscopy. Evidence was found for the formati on of a 1:1 complex in which the HCl molecule binds to the C=C double bond. Weaker bands due to the two different 1:2 complexes derived from the 1:1 c omplex were observed. From spectra recorded at different temperatures betwe en 90 and 130 K, the complexation enthalpy for the 1:1 complex formed was d etermined to be -9.9(3) kJ mol(-1), while the corresponding value for the m ost stable 1:2 complex, MeCP . HCl . HCl, was determined to be -14.6(4) kJ mol(-1). Structural and spectral information for the 1:1 and the 1:2 comple xes was obtained from DFT calculations at the B3LYP/6-311++G(d,p) level. Us ing free energy perturbation Monte Carlo simulations to calculate the solve nt influences, and statistical thermodynamics to account for zero-point vib rational and thermal contributions, the complexation energies for the 1:1 c omplex and the 1:2 complex were estimated from the experimental complexatio n enthalpies to be -16.9(12) and -28.7(14) kJ mol(-1). These numbers are co mpared with single-point energies calculated at the MP2/aug-cc-PVTZ level.