Synthesis, molecular structure, vibrational and theoretical studies of a new non-centrosymmetric organic sulphate with promising NLO properties

Abstract

The new non-centrosymmetric inorganic-organic hybrid material tetrakis(2,6-dimethylpiperazine-1,4-diium) tetrakis(sulfate) dihydrate (DMPS) has been prepared and crystallized in the non-centrosymmetric space group Cc of the monoclinic system with the crystallographic parameters: a = 25.044 (4) Å, b = 12.1046 (18) Å, c = 14.075 (2) Å, β = 107.289 (5) °, V = 4074.0 (10) Å3 and Z = 4. The tetrahedron (S(1)O42−) and (S(4)O42−) anions are connected to water molecules forming as infinite chains type C44(12) along the c-axis in y = ¼ and ¾. The 2,6-dimethylpiperazine-1,4-diium cations are correlated to the inorganic part by means of NH⋯O and CH⋯O hydrogen bonds. The diprotonated piperazine ring endorses a chair conformation, with the methyl groups placing in an equatorial site. Intermolecular contacts in the crystal structure were computed by Hirshfeld surface examination. Infrared spectrum proves the presence of the functional groups in the synthesised salt and different coordination modes are observed in the sulfate groups. Optical propriety affirms a noteworthy band gap energy signifying steadiness of the title compound. Furthermore, the polarizability and first order hyperpolarizability of the title molecule were calculated and interpreted. Subsequently, theoretical calculations indicate that first order hyperpolarizability is 13 times greater than urea. Moreover, the thermodynamic properties (heat capacity, entropy, and enthalpy) of the title compound at different temperatures were calculated in gas phase. Additionally, two neutral, one anionic and the hydrated species experimentally observed by X-ray diffraction were identified in the vibrational infrared spectrum of DMPS combining the experimental spectrum with the corresponding predicted by using DFT calculations and the scaled quantum mechanical force field (SQMFF) procedure.