van der Waals Complexes between Carbonyl Fluoride and Boron Trifluoride Observed in Liquefied Argon, Krypton, and Nitrogen: A FTIR and ab Initio Study

The IR spectra (4000-400 cm - 1 ) of COF 2 /BF 3 mixtures, dissolved in liquefied argon (LAr), krypton (LKr), and nitrogen (LN 2 ), have been examined. In all spectra evidence was found for the formation of a 1:1 van der Waals complex. Using spectra recorded at several temperatures between 81 and 172 K the complexation enthalpies Δ H ° in LAr, LKr, and LN 2 were determined to be −11.8(3), −10.6(3), and −7.8(3) kJ mol - 1, respectively. A theoretical study, using both density functional theory at the B3LYP/6-311++G(d,p) level and ab initio at the MP2/aug-cc-pVTZ level, indicates that the complexation can occur either via the oxygen or via a fluorine atom of COF 2 . From a comparison of the experimental and calculated frequencies it was concluded that the observed complex bands are due to a species in which the boron atom coordinates with the oxygen lone pairs. The complexation energy Δ c E is obtained from the Δ H ° by correcting for solvent influences, and thermal contributions equals −15.0(6) kJ mol - 1 . This value agrees well with the MP2/aug-cc-pVTZ level result, −12.4 kJ mol - 1 . The complexation entropy Δ S ° has been found to be influenced by the solvent and is correlated with Δ H °. This correlation reflects the existence of the compensation effect for the thermodynamics of van der Waals complexes.