A New Mononuclear Complex: Structure, Vibrational (FT-IR and Raman), Hirshfeld Surfaces Analysis, Electrical Properties and Equivalent Circuit

Abstract

The present paper aims to develop the synthesis, crystal structure, and properties of Zn(C7H5NO4)Cl2.H2O compound investigated by vibrational study, thermal analysis and dielectric measurements. The single crystal X-ray diffraction investigation reveals that the studied compound crystallizes in the orthorhombic system with space group Pnna according to the following lattice parameters: a=13.8816(4) A, b=10.3602(3) A, c=7.8967(2) A and Z=4. The presence of the key functional groups in the molecule has already been confirmed by Fourier transform infrared (FT-IR) analysis. Thermal behaviour of this sample, studied by TGA and DSC exhibit two anomalies at 345 and 386K. The hydrogen bonding plays a significant role in the stabilization of the structure. Such a parallel displaced structure has also a contribution from π-σ non-covalent interactions (C-H…π and C-O…π stacking between the C-H groups and C-O groups with the benzene rings). The dipicolonic acid (2,6-pyridinedicarboxylic acid) ligand coordinated to the Zn(II) ions through a nitrogen atom of pyridine ring, two oxygen atom of carboxylic group and two chloride atoms as a tridentate ligand. Hirshfeld surface analysis of the intermolecular interactions in crystal structures have been used to scrutinize molecular shapes. The characteristic features of 13C solid state CP/MAS-NMR applications showed five isotropic resonances, confirming the structure determined by XRD. Its dielectric properties as a function of temperature and frequency in the ranges 298-418 K and 209 Hz-5 MHz are measured. The Cole-Cole (Z’ versus Z’’) plots are analyzed by fitting to an equivalent electrical circuit model, consisting of a circuit elements; grain, grain boundary, electrode-solid interface polarization and Warburg resistance. Each circuit elements is formed by a parallel combination resistance (R) and constant phase elements (CPE). The grain conductivity as well as the activation energy depending to of temperature, via impedance technique, besides the activation energy due to relaxation time as function of temperature, have been studied showing two anomalies, which are also detected by the TGA and DSC. They could be explained by not only a phase transition and reorientation hopping between equivalent sites at 343K but also the disappearance of the water molecule of the structure at 388K.