Preparation, Crystal Structure, Supramolecular Assembly, and DFT Studies of Two Organic Salts Bearing Pyridine and Pyrimidine

The effective preparation of two new pyrimidine- and
pyridine-based
organic crystalline salts with substituted acidic moieties (i.e.,
(Z)-4-(naphthalen-2-ylamino)-4-oxobut-2-enoic acid
(DCNO) and 2-hydroxy-3,5-dinitrobenzoic acid (PCNP)) using methanol as a solvent has been reported. These molecular
salts have ionic interactions that are responsible for their structural
stabilization in their solid-state assemblies. The crystal structures
of DCNO and PCNP were determined by the
single-crystal X-ray diffraction (SCXRD) technique. The SCXRD study
inferred that cations and anions are strongly packed due to N–H···O,
N–H···N, and C–H···O noncovalent
interactions in DCNO, whereas in PCNP, N–H···N
noncovalent interactions are absent. The noncovalent interactions
in both organic crystalline salts were comprehensively investigated
by Hirshfeld surface analysis. Further, a detailed density functional
theory (DFT) study of both compounds was performed. The optimized
structures of both compounds supported the existence of the H-bonding
and weak dispersion interactions in the synthesized organic crystalline
salt structures. Both compounds were shown to have large and noticeably
different HOMO/LUMO energy gaps. The atomic charge analysis results
supported the SCXRD and HSA results, showing the formation of intermolecular
noncovalent interactions in both organic crystalline salts. The results
of the natural bond orbital (NBO) analysis confirmed the existence
of (relatively weak) noncovalent interactions between the cation and
anion moieties of their organic crystalline salts. The global reactivity
parameters (GRPs) analysis showed that both organic crystalline salts’
compounds should be quite thermodynamically stable and that DCNO should be less reactive than PCNP. For both
compounds, the molecular electrostatic potential (MEP) analysis results
support the existence of intermolecular electrostatic interactions
in their organic crystalline salts.