Abstract
The new mol-ecular nickel(II) complex, namely, {4-bromo-2-[({N'-[(2-oxidobenzylidene)amino]carbamimidoyl}imino)methyl]phenolato}nickel(II) N,N-di-methyl-formamide solvate monohydrate, [Ni(C15H11BrN4O2)]·C3H7NO·H2O, (I), crystallizes in the triclinic space group P with one mol-ecule per asymmetric unit. The guanidine ligand is a product of Schiff base condensation between amino-guanidine, salicyl-aldehyde and 5-bromo-salicyl-aldehyde templated by Ni2+ ions. The chelating ligand mol-ecule 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 mol-ecule adopts an almost planar conformation. In the crystal, a complicated hydrogen-bonded network is formed through N-H⋯N/O and O-H⋯O inter-molecular inter-actions. 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.
Highlights
NiII molecular complex with a tetradentate aminoguanidine-derived Schiff base ligand: structural, spectroscopic and electrochemical studies and photoelectric response
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 A, cis angles in the range 83.08 (5)–95.35 (5), trans angles of 177.80 (5) and 178.29 (5)]
Summary
The functional group on the side chain of arginine, has attracted much attention in the fields of drug development (Santos et al, 2015; Hirsh et al, 2008) and natural product synthesis (Berlinck & Romminger, 2016; Kudo et al, 2016). The condensation reactions of aminoguanidine freshly liberated from AGÁHCl or AGÁHNO3 and arylaldehydes (salicylaldehyde, 5-bromosalicylaldehyde, pyridine-2-carbaldehyde) produced the expected 1:1 Schiff base ligands isolated as protonated cations of nitrate or chloride salts as well as CuII and CoIII mononuclear complexes (Buvaylo et al, 2013, 2016, 2017). The dichloridocopper(II) complex bearing a pyridine-2-carbaldehyde aminoguanidine Schiff base ligand revealed prominent catalytic activity towards the oxidation of cyclohexane with hydrogen peroxide in the presence of various promoters (Buvaylo et al, 2017). We attempted to synthesize an Ni complex with the Schiff base ligand derived from AG and salicylaldehyde. The new tetradentate ligand (2-hydroxybenzylidene)(5-bromo-2-hydroxybenzylidene)aminoguanidine, H2L, was formed from the in situ condensation of one AG molecule and two different molecules of the aldehydes in the presence of Ni2+ ions.
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