Crystal structure and spectroscopic properties of the 1:1 complex of pyridine betaine with p-hydroxybenzoic acid

Crystal structure of the 1:1 complex of pyridine betaine (PyB) with p-hydroxybenzoic acid (HBA) has been determined by X-ray diffraction. The crystals are monoclinic, space group P21/c with the unit cell parameters a = 11.9009(4), b = 10.3283(3), c = 11.0616(4) Å and β = 104.252(4)°, Z = 4, R = 0.038. Both oxygen atoms of the carboxylate group of PyB are linked with the carboxylic and hydroxyl groups of HBA of the neighboring molecules, through two O–H⋯O hydrogen bonds of 2.589(1) and 2.588(2) Å, respectively. The PyB and HBA molecules are connected into infinite chains parallel to the x-axis. The FTIR spectrum of the solid complex is consistent with the X-ray results. 1H and 13C chemical shifts of the title complex in D2O and DMSO-d6 and the GIAO/B3LYP/6-31G(d,p) calculated magnetic isotropic shielding tensors (σ) using the screening solvation model (COSMO), δexp = a + bσ, are reported. In the theoretically optimized structures of the complex investigated the O⋯O distances between PyB and HBA are not the same.