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
.