Crystal structure, optical properties, Hirshfeld surface analysis and antibacterial activity of a new organic-inorganic metal halide: 4-nitrobenzyl-4-methylpyridinium tetrachlorocobaltate(II)

Abstract

This paper presented the synthesis, composition analysis, and structural characterization of a new organo-inorganic metal halide, 4-nitrobenzyl-4-methylpyridinium tetrachlorocobaltate(II) [4NO2Bz-4-MePy]2[CoCl4](1). The single-crystal X-ray diffraction analysis displayed that the compound crystallized in the monoclinic space group P21/c, consisting of two [4NO2Bz-4-MePy]+ cations and a [CoCl4]2− anion. The energy gap between the HOMO and LUMO orbitals, the polarizability, and the first hyperpolarizability were carried out based on the DFT calculation. The HOMO-LUMO energy gap and UV-visible diffuse reflectance spectrum illustrated the charge transfer interactions between the [CoCl4]2− anions and the [4NO2Bz-4-MePy]+ cations. In addition, the low band gap values (1.64 eV for the Tauc formula, 1.62 eV for the truncated line method, and 2.73 eV for the calculated value) indicated that the crystal was appropriate for optical applications. The first hyperpolarizability (βtot) was 342 times higher than that of standard KDP crystal (βKDP = 6.85 × 10−31 esu), suggesting that crystal 1 was a premium material for NLO applications. The scanning electron microscopy and energy dispersive spectrometer determined the morphology and elemental distribution of the crystal. Hirshfeld surface analysis was performed to quantify the contributions of the different intermolecular interactions. The result of antimicrobial experiments displayed that the compound had excellent antimicrobial activity against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli).