Experimental and computational study of a hybrid phosphate crystal exhibiting a wide energy band gap: Structural, optical, and insight from Hirshfeld surface analysis and DFT calculations

Abstract

The crystal structure of C₄H₁₀NO₃⁺.H₂PO₄⁻ reveals a three-dimensional hydrogen-bonded network composed of dihydrogen phosphate anions, carboxyl groups, and ammonium groups, the molecular geometry of DLTDP was optimized using Becke's three-parameter hybrid functional, the Lee-Yang-Parr correlation functional (B3LYP) theory, and the 6-311G basis set. Additionally, fingerprint plots derived from the Hirshfeld surface were employed to explore the crystal's intermolecular interactions and the compound, H⋯H contacts appear as asymmetrically scattered dots, covering a large area of the two-dimensional FP maps, with a single broad peak at de = di ∼ 1.2 Å and a significant contribution of 33.6 %. O⋯H/H⋯O contacts, However, the volume occupied by these voids represents about 9.56 % of the volume of the unit cell. The nonlinear optical (NLO) properties of DLTDP were also theoretically predicted. Its electronic properties, including HOMO and LUMO energies, were computed to assess the charge transfer characteristics. Local reactivity descriptors, such as electrophilicity indices, were used to identify the most reactive sites. To investigate the electronic structure and intra/intermolecular charge transfer within the DLTDP molecule, Natural Bond Orbital (NBO) analysis was employed. This approach provided detailed insights into donor–acceptor interactions and the stabilization energies associated with electron delocalization. The nucleophilic and electrophilic regions were determined through molecular electrostatic potential (MEP) mapping and Fukui function analysis. The IR spectra exhibited a broad absorption band around 2350 cm⁻¹, attributed to the O–H stretching vibration of the H₂PO₄⁻ group, indicating the formation of hydrogen bonds between H₂PO₄⁻ anions and N–H groups. In addition, the interaction of the investigated compound with COVID-19 target proteins was studied. Molecular dynamics simulations were performed over a time scale of 0–100 ns to analyze its interaction with the protein exhibiting the lowest docking energy. Finally, the DLTDP crystal showed an optical band gap of 5.87 ± 0.01 eV, indicating its potential suitability for optical applications due to its wide band gap.