Three new complexes of Zn(II) with a quinoline based Schiff base ligand: Syntheses, crystal architectures, Hirshfeld surface analyses, DFT study, photoluminescence and thermal properties

Abstract

This report deals with one dinuclear and two mononuclear zinc(II) complexes of compositions [Zn2L2(μ1,1-N3)(N3)] (1), [ZnL(NCO)(H2O)] (2) and [ZnL(NCS)(H2O)] (3), where HL ((E)-2-ethoxy-6-((quinolin-8-ylimino)methyl)phenol)) is the 1:1 condensation product of 3-ethoxysalicylaldehyde and 8-aminoquinoline. All the three metal complexes have been characterized by C, H, N elemental analyses, FT-IR spectra, single crystal X-ray structures and powder XRD. The structures of 2 and 3 are isomorphous. The metal centres in 1–3 are five coordinated and adopt vacant octahedral or distorted square pyramidal geometry for 1 and distorted trigonal bipyramidal geometry for 2 and 3. Supramolecular interactions and topologies in all the three crystal structures have been analyzed, revealing 3–D assemblies in 1–3 due to a number of non-covalent interactions (C–H∙∙∙O, C–H∙∙∙N and π∙∙∙π in 1; C–H∙∙∙O, O–H∙∙∙O, O–H∙∙∙N, π∙∙∙π and C–H∙∙∙π in 2; C–H∙∙∙S, O–H∙∙∙O, O–H∙∙∙N, π∙∙∙π and C–H∙∙∙π in 3). To gain additional insight into the intermolecular contacts and their relative contributions towards the packing, Hirshfeld surface analyses have been undertaken for 1–3 and demonstrated in detail with respect to structural parameters, depressions in surfaces, fingerprint plots and enrichment ratios. The thermo-gravimetric and differential thermal analyses (TG/DTA) have been performed and the decomposition patterns are well explained. Steady state and time resolved fluorescence properties have been investigated. Optical band gaps have been determined from the data of the UV-Vis spectra. DFT calculations have been undertaken. The DFT computed HOMO-LUMO gaps corroborate the optical gaps and the DFT computed electrostatic potential (ESP) surfaces rationalize the supramolecular interactions nicely.