Hydrogen-bonded complexes of trimethyl phosphate and fluoroform: A matrix isolation infrared and ab initio study

Trimethyl phosphate (TMP) and fluoroform (CHF3) were co-deposited in a nitrogen matrix and complexes of these species were identified using infrared spectroscopy. Formation of the complexes was evidenced by the shifts in the vibrational frequencies of the modes involving the TMP and CHF3 submolecule. The structures of these complexes, energies and the vibrational frequencies were computed at the B3LYP/6-31++G(d,p) level. Both the experimental and computational studies indicated two types of TMPCHF3 complexes; one in which the hydrogen of CHF3 was bonded to the phosphoryl oxygen and another in which the bonding was at the alkoxy oxygen of the phosphate. In addition to the primary hydrogen-bonded interaction at the phosphoryl and alkoxy oxygen, these complexes also appeared to be stabilized by a secondary and weaker interaction between the methyl hydrogen in TMP and the fluorine in CHF3. The computed vibrational frequencies in the complexes agreed well with the observed frequencies. The stabilization energies of these complexes, corrected separately for zero-point energies and basis set superposition error were ≈−5.0 and −5.24 kcal/mol for the phosphoryl complexes and ≈−2.8 and −0.57 kcal/mol for the alkoxy complexes respectively. The nature of the bonding in this complex was also studied using the atom-in-molecule theory, which clearly showed a (3, −1) bond critical point between the two submolecules.