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 COF2/BF3 mixtures, dissolved in liquefied argon (LAr), krypton (LKr), and nitrogen (LN2), 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 ΔH°in LAr, LKr, and LN2 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 COF2. 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 ΔH°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 ΔS°has been found to be influenced by the solvent and is correlated with ΔH°. This correlation reflects the existence of the compensation effect for the thermodynamics of van der Waals complexes