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 Li quefied argon (LAr), krypton (LKr), and nitrogen (LN2), have been exam ined. In all spectra evidence was found for the formation of a 1:1 van der Waals complex. Using spectra recorded at several temperatures bet ween 81 and 172 K the complexation enthalpies Delta H degrees 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 functio nal theory at the B3LYP/G-311++G(d,p) level and ab initio at the MP2/a ug-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 e xperimental and calculated frequencies it was concluded that the obser ved complex bands are due to a species in which the boron atom coordin ates with the oxygen lone pairs. The complexation energy Delta(c)E is obtained from the Delta H degrees by correcting for solvent influences , and thermal contributions equals -15.0(6) kJ mol(-1). This value agr ees well with the MP2/aug-cc-pVTZ level result, -12.4 kJ mol(-1). The complexation entropy Delta S degrees has been found to be influenced b y the solvent and is correlated with Delta H degrees. This correlation reflects the existence of the compensation effect for the thermodynam ics of van der Waals complexes.