Ni^IImolecular complex with a tetradentate aminoguanidine-derived Schiff base ligand: structural, spectroscopic and electrochemical studies and photoelectric response

Abstract

The new molecular nickel(II) complex, namely, {4-bromo-2-[({N′-[(2-oxidobenzylidene)amino]carbamimidoyl}imino)methyl]phenolato}nickel(II) N,N-dimethylformamide solvate monohydrate, [Ni(C15H11BrN4O2)]·C3H7NO·H2O, (I), crystallizes in the triclinic space group P\overline{1} with one molecule per asymmetric unit. The guanidine ligand is a product of Schiff base condensation between aminoguanidine, salicylaldehyde and 5-bromosalicylaldehyde templated by Ni2+ ions. The chelating ligand molecule is deprotonated at the phenol O atoms and coordinates the metal centre through the two azomethine N and two phenolate O atoms in a cis-NiN2O2 square-planar configuration [average(Ni—N/O) = 1.8489 Å, cis angles in the range 83.08 (5)–95.35 (5)°, trans angles of 177.80 (5) and 178.29 (5)°]. The complex molecule adopts an almost planar conformation. In the crystal, a complicated hydrogen-bonded network is formed through N—H...N/O and O—H...O intermolecular interactions. Complex (I) was also characterized by FT–IR and 1H NMR spectroscopy. It undergoes an NiII ↔ NiIII redox reaction at E 1/2 = +0.295 V (vs Ag/AgCl) in methanol solution. In a thin film with a free surface, complex (I) shows a fast photoelectric response upon exposure to visible light with a maximum photovoltage of ∼178 mV.

Solution Equilibrium Studies on Salicylidene Aminoguanidine Schiff Base Metal Complexes: Impact of the Hybridization with L-Proline on Stability, Redox Activity and Cytotoxicity

“…Schiff bases (imines) and their transition metal complexes are widely investigated and considered as key classes of medicinal compounds due to their enormous potential for pharmacological activities such as anticancer, antibacterial and antioxidant effects [ 8 , 9 ]. Among the metal complexes of aminoguanidine-based Schiff bases, the Cu(II) complexes formed with salicylidene aminoguanidine or pyridoxilidene aminoguanidine are the most common [ 3 , 4 , 6 , 10 , 11 ], although we can find examples for V(V), Co(III) or Ni(II) complexes as well [ 5 , 6 , 10 , 12 , 13 ]. The Cu(II) complex of the (N,N,O) donor containing a Schiff base of aminoguanidine formed with salicylaldehyde (2-(2-hydroxybenzylidene)hydrazinecarboximidamide, SISC, Scheme 1 ) displayed significant cytotoxic activity on a colorectal cancer cell line (HCT1) and strong DNA-binding affinity [ 3 ].…”