Computer simulation study of the intermolecular structure of phosphoric acid-N,N-dimethylformamide mixtures.

The structures and energies of the complexes (H3PO4)2, H3PO4-DMF, and (H3PO4)2-DMF were analyzed at the B3LYP level of approximation. It was found that H-bonds form between H3PO4 and DMF molecules, but the strength of the H-bond depends strongly on its molecular environment. Effects of the solvent were taken into account via the CPCM approach. According to the B3LYP-СPCM calculations, the O···O distance in (H3PO4)2-DMF is shorter and its H-bonds are stronger than in the other complexes studied. In order to study the effects of concentration on the intermolecular structure, molecular dynamics simulations of H3PO4-DMF mixtures with mole fractions of acid of <0.1 were performed. The calculations indicated that the largest fraction of the acid protons are involved in hydrogen bonding with oxygen atoms of the DMF molecules. An increased probability of acid-acid hydrogen-bond formation at phosphoric acid mole fractions >0.06 was also noted.