Synthesis, Crystal Structures, and Density Functional Theory Studies of Two Salt Cocrystals Containing Meldrum’s Acid Group

Abstract

Two salt cocrystals, C 31 H 34 N 4 O 8 ( DDD ) and C 17 H 20 N 2 O 8 ( MDD ), were synthesized and their structures were determined by single-crystal X-ray diffraction. DDD is made up of one (C 13 H 13 O 8 ) − anion, one (C 9 H 11 N 2 ) + cation, and one 5,6-dimethyl-1 H -benzo[ d ]imidazole molecule. MDD consists of one (C 4 H 7 N 2 ) + cation and one (C 13 H 13 O 8 ) − anion. DDD and MDD belong to the monoclinic, P 21/ c space group and triclinic, P -1 space group, respectively. A 1D-chained structure of DDD was constituted by N–H···N and N–H···O hydrogen bonds. However, a 1D-chained structure of MDD was bridged by N–H···O hydrogen bonds. Their density functional theory-optimized geometric structures with a B3LYP/6-311G(d,p) basis set fit well with those of crystallographic studies. By calculating their thermodynamic properties, the correlation equations of C 0 p , m , S 0 m , H 0 m , and temperature T were obtained. By comparing the experimental electronic spectra with the calculated electronic spectra, it is found that the PBEPBE/6-311G(d,p) method can simulate the UV–Vis spectra of DDD and MDD . In addition, the fluorescence spectra in the EtOH solution analysis show that the yellowish-green emission occurs at 570 nm (λ ex = 310 nm) for DDD and the purplish-blue emission occurs at 454 nm (λ ex = 316 nm) for MDD .