Synthesis, crystal structure, DFT/TDDFT calculation, photophysical properties and DNA binding studies of morpholino moiety ligand based two Cu(ii) complexes in combination with carboxylates

Abstract

The complexes [Cu(L)(pa)] (1) and [Cu(L)(mb)] (2) (HL = o-{(3-morpholinopropylimino)methyl}phenol; pa = 3-phenylacrylate; mb = p-methylbenzoate) have been synthesized and characterized by elemental analysis, single crystal X-ray crystallography, FT-IR, UV-vis electronic absorption spectroscopic analysis. Complexes 1 and 2 are mononuclear with distorted square pyramidal geometries where the Schiff base coordinates to copper(II) in the tridentate (O, N, N) chelating mode. These three atoms plus one carboxylate oxygen define the equatorial plane of the square pyramid while the axial position is occupied by carboxylate oxygen at a relatively longer distance. Weak C–H⋯π interactions result the formation of 2D supramolecular structures for both complexes. At room temperature complexes 1 and 2, exhibit fluorescence with a quantum yield (Φ_s) of 0.129 and 0.117, respectively. The UV-vis electronic absorption and IR spectral data of complexes have been compared with the results obtained by employing DFT and time dependent density functional theory (TD-DFT) calculation using the B3LYP, B3PW91 and MPW1PW91 functionals, with LanL2DZ basis set. The results of these calculations are functional-dependent and among the functionals, B3LYP proved to better reproduce the experimental results. The interactions of complexes with the calf thymus DNA (CT-DNA) were investigated using electronic absorption and fluorescence spectroscopic techniques. The studies reveal that the binding affinities of complexes 1 and 2 with CT-DNA are in the order of 1.68 × 10⁵ M⁻¹ and 2.271 × 10⁵ M⁻¹, respectively. A study of the effect of various metal ions on the electronic absorption and fluorescence spectra of HL reveals that it selectively senses the Cu(II) ions.