Synthesis, characterization, TDDFT calculation and biological activity of tetradentate ligand based square pyramidal Cu(ii) complexes

Abstract

Distorted square pyramidal complexes [Cu(L¹)(H₂O)]·ClO₄ (1), [Cu(L²)(H₂O)]·ClO₄ (2) and [Cu(L³)(H₂O)]·ClO₄ (3) (HL¹ = o-{[2-(2-aminoethylamino)ethylimino]methyl}phenol; HL² = 2-{[2-(2-aminoethylamino)ethylimino]methyl}-6-methoxyphenol; HL³ = o-{1-[2-(2-aminoethylamino)ethylimino]ethyl}phenol) have been synthesized, and characterized by X-ray crystallography and spectroscopic analysis. All the complexes exhibit fluorescence at room temperature [λ_ex = 267 nm, λ_em = 312, 329 and 357 nm, φ = 0.52 for 1; λ_ex = 272 nm, λ_em = 312, 329 and 355 nm, φ = 0.46 for 2; λ_ex = 265 nm, λ_em = 312, 356 and 377 nm, φ = 0.33 for 3]. The electronic structure and photophysical properties of the ligands and complexes were calculated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods using the B3LYP, B3PW91 and MPW1PW91 functionals, with 6-31G (d-p) and LanL2DZ basis sets. The results of TD-DFT calculations are functional-dependent and among the functionals, B3LYP was able to best reproduce the experimental results. Catecholase activity of 1–3 has been investigated using 3,5-di-tert butyl catechol (3,5-DTBC) as the model substrate and found that complexes are active for catalyzing the aerobic oxidation of 3,5-DTBC to 3,5-di-tert butyl benzoquinone (3,5-DTBQ). The compound with more distorted square pyramidal geometry shows a higher rate of catalytic activity. All the complexes have been tested for their anticancer activities in human breast (MCF7) cancer cell lines. Complexes show dose dependent suppression of cell viability with IC₅₀ values 30, 68 and >100 μM for 1, 2 and 3, respectively. Anticancer activities of 1–3 and cisplatin were compared, and found that 1–3 were relatively less active than cisplatin.