3-Phenylpyridinium hydrogen squarate: Experimental and computational study of a nonlinear optical material

•Non-linear optical material.•Supramolecular architectures.•IR, UV spectroscopy and single crystal XRD.•Ab initio calculations.•Squaric acid and hydrogen squarate anions form α-dimer.

The detailed investigation of an organic nonlinear optical (NLO) squarate salt of 3-phenylpyridinium hydrogen squarate (1), C11H10N+·C4HO4−, was reported in this study. The XRD data indicates that the crystal structure of the title compound is in the triclinic P-1 space group. In the asymmetric unit, the 3-phenylpyridine molecule is protonated by one hydrogen atom donation of squaric acid molecule, forming the salt (1). The X-ray analysis shows that the crystal packing has hydrogen bonding ring pattern of D22(10) (α-dimer) through NH···O interactions. The structural and vibrational properties of the compound were also studied by computational methods of ab initio at DFT/B3LYP/6-31++G(d,p) (2) and HF/6-31++G(d,p) (3) levels of theory. The calculation results on the basis of two models for both the optimized molecular structure and vibrational properties for the 1 are presented and compared with the experimental results. Non-linear optical properties (NLO) of the title compound together with the molecular electrostatic potential (MEP), electronic absorption spectrum, frontier molecular orbitals (FMOs) and conformational flexibility were also studied at the 2 level and the results were reported. In order to evaluate the suitability for NLO applications thermal analysis (TG, DTA and DTG) data of 1 were also obtained.

Graphical abstractThe X-ray analysis clearly indicated that the crystal packing has shown the hydrogen bonding ring pattern of D22(10) (α-dimer) through NH⋯O interactions. The hydrogen squarate anions form α-dimer, while 3-phenylpyridinium molecule interacts through NH⋯O and CH⋯O with the hydrogen squarate anion.Figure optionsDownload full-size imageDownload as PowerPoint slide