Spectroscopic investigations on La3+, Pr3+, Nd3+ and Gd3+ complexes with a multidentate ligating system: Luminescence properties and biological activities

Abstract

A series of eight complexes of Ln chlorides and perchlorates (Ln = La3+, Pr3+, Nd3+ and Gd3+) with the ligand, L2− (H2L = 2,2′-iminobis [N-(3-hydroxypropyl)acetamide]), are prepared and characterized by spectral (FTIR, FAB mass, and UV–Visible, 1D and 2D NMR), thermal, electrochemical and density functional theory (DFT) studies. The analytical and spectral data confirmed the composition to be [LnLCl(H2O)2]·2H2O {La3+(1), Pr3+(2), Nd3+(3) and Gd3+(4)} and [LnLClO4(H2O)2]·H2O {La3+(5), Pr3+(6), Nd3+(7) and Gd3+(8)}. The spectral data ascertained a hepta-coordinate geometry of the complexes, which was further supported from DFT studies. Analytical and thermal data supported the stoichiometry of the complexes. The oscillator strengths and the covalency parameters (β, b1/2 and δ) were evaluated from electronic (UV–Vis) spectral studies. The complexes exhibited moderate emission in the luminescence spectra of Pr3+ and Nd3+. Cyclic voltammetric studies confirm the formation of quasi-reversible (PrIII/IV and GdIII/IV) redox couples in solution. Complexes and the free ligand were tested for antibacterial and antifungal properties. Molecular docking results ascertain the comparable binding affinity of the neutral ligand (H2L), complex (4) and complex (8) with B-DNA.