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

Abstract

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 Δc 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.

Enthalpy–Entropy Correlation for Hydrogen Adsorption on MOFs: Variable‐Temperature FTIR Study of Hydrogen Adsorption on MIL‐100(Cr) and MIL‐101(Cr)

“…Hence, referring to absolute values, a greater ΔH 0 will result in a correspondingly greater ΔS 0 . In fact, a positive correlation between ΔH 0 and ΔS 0 (sometimes referred to as entropy-enthalpy compensation) was also reported several times in the literature for a range of chemical processes involving weak interaction forces; among them are formation of weakly associated molecular complexes, [57,58] weak hydrogen bonding [59,60] and Langmuir-type adsorption from solution. [59] Regarding lo- CPO-27-Co 11.2 130 [34] (Mg,Na)-Y 18 136 [44] (Ca,Na)-Y 15 127 [54] Ca-X 12.5 118 [54] Mg-X 13 114 [48] Li-FER 4.1 57 [46] Na-FER 6 78 [53] K-FER 3.5 57 [53] Li-ZSM-5 6.5 90 [55] Na-ZSM-5 10.3 121 [52] [a] Referred to a standard state at 1 Torr (1.32 mb).…”

H2 interaction with divalent cations in isostructural MOFs: a key study for variable temperature infrared spectroscopy

“…Besides H 2 adsorption in zeolites, 80,83 such a trend, already referred to as entropy-enthalpy compensation, was observed in the literature for a range of chemical processes involving weak interaction forces such as the formation of weakly associated molecular complexes, 84,85 weak hydrogen bonding 86,87 and Langmuir-type adsorption from solution. 86 The −ΔH 0 ∝ −ΔS 0 correlation is related to the fact that the stronger the interaction between hydrogen molecules and the adsorbing centre is, the greater will be the corresponding decrease of H 2 motion freedom, which results in an increasing order of the system.…”

Probing zeolites by vibrational spectroscopies

“…Besides molecular adsorption in zeolites, 735,736,742 such a trend, already referred to as entropyenthalpy compensation, has been observed in the literature for a range of chemical processes that involve weak interaction forces such as the formation of weakly associated molecular complexes, 743,744 weak hydrogen bonding 745,746 and Langmuirtype adsorption from solution. Besides molecular adsorption in zeolites, 735,736,742 such a trend, already referred to as entropyenthalpy compensation, has been observed in the literature for a range of chemical processes that involve weak interaction forces such as the formation of weakly associated molecular complexes, 743,744 weak hydrogen bonding 745,746 and Langmuirtype adsorption from solution.…”