New symmetrical dinucleating ligand based assembly of bridged dicopper(II) and dizinc(II) centers: Synthesis, structure, spectroscopy, magnetic properties and glycoside hydrolysis

Abstract

Two dinuclear copper(II) complexes [Li(H2O)3(CH3OH)]4[Cu2Br4][Cu2(cpdp)(μ-O2CCH3)]4(OH)2 (1), [Cu(H2O)4][Cu2(cpdp)(μ-O2CC6H5)]2Cl2·5H2O (2), and a dinuclear zinc(II) complex [Zn2(cpdp)(μ-O2CCH3)] (3) have been synthesized using pyridine and benzoate functionality based new symmetrical dinucleating ligand, N,N′-Bis[2-carboxybenzomethyl]-N,N′-Bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol (H3cpdp). Complexes 1, 2 and 3 have been synthesized by carrying out reaction of the ligand H3cpdp with stoichiometric amounts of [Cu2(O2CCH3)4(H2O)2], CuCl2·2H2O/C6H5COONa, and Zn(CH3COO)2·2H2O, respectively, in methanol in the presence of NaOH at ambient temperature. Characterizations of the complexes have been done using various analytical techniques including single crystal X-ray structure determination. The X-ray crystal structure analyses reveal that the copper(II) ions in complexes 1 and 2 are in a distorted square pyramidal geometry with Cu---Cu separation of 3.455(8)Å and 3.492(1)Å, respectively. The DFT optimized structure of complex 3 indicates that two zinc(II) ions are in a distorted square pyramidal geometry with Zn---Zn separation of 3.492(8)Å. UV–Vis and mass spectrometric analyses of the complexes confirm their dimeric nature in solution. Furthermore, 1H and 13C NMR spectroscopic investigations authenticate the integrity of complex 3 in solution. Variable-temperature (2–300K) magnetic susceptibility measurements show the presence of antiferromagnetic interactions between the copper centers, with J=−26.0cm−1 and −23.9cm−1 (Ĥ=−2JS1S2) in complexes 1 and 2, respectively. In addition, glycosidase-like activity of the complexes has been investigated in aqueous solution at pH∼10.5 by UV–Vis spectrophotometric technique using p-nitrophenyl-α-d-glucopyranoside (4) and p-nitrophenyl-β-d-glucopyranoside (5) as model substrates.