Synthesis, structures and catecholase activity of a new series of dicopper(II) complexes of reduced Schiff base ligands

A series of dinuclear Cu-II complexes of reduced Schiff bases from substituted salicylaldehydes and amino acids have been synthesized and characterized. They are: [Cu-2(RScp11)(2)-(H2O)(2)] {H(2)RScp11 = 1-[(2-hydroxy-5-R-benzyl)amino] cyclo-pentane-1-carboxylic acid; R = H (1), C1 (2), CH3 (3), OH (4)), [Cu-2(RSch11)(2)(H2O)(x)] {H(2)RSch11 = 1-[(2-hydroxy-5-R-benzyl)aminolcyclohexane-1-carboxylic acid; R = H and x = 1 (5), R = C1 and x = 2 (6), R = CH3 and x = 2 (7)), [Cu-2(RSch12)(2)-(H2O)(2)] {H(2)RSch12 = 2- [(2-hydroxy-5-R-benzyl)amino]cyclohexane-1-carboxylic acid; R = H (8), CH3 (10) and [Cu-2(ClSch12)(2)]center dot 2H(2)O (9)}, {Cu-2(Diala5)(2)(H2O)(2)]center dot H2O [H-3-Diala5 = N-(2,5-dihydroxybenzyl)-L-alanine] (11), [Cu-2(Diala4)(2)(H2O)(2)center dot H2O [H(3)Diala4 = N-(2,4-dihydroxybenzyl)L-alanine] (12), and [Cu-2(Diala3)(2)(H2O)(2)]center dot H2O [H(3)Diala3 = N-(2,3-dihydroxybenzyl)-L-alanine] (13). They were isolated and characterized by chemical and spectroscopic methods. Single crystal X-ray crystallographic studies have revealed that [Cu-2(Scp11)(2)(MeOH)(2)] (1a), [Cu-2(ClScp11)(2)(DMF)-(H2O)]center dot MeCN (2a), [Cu-2(MeScp11)(2)(MeOH)(2)]center dot 2MeOH (3a), [Cu-2(ClSch11)(2)(MeOH)(2)]center dot 2MeOH (6a), [Cu2(ClSch12)(2)]center dot 2MeOH (9a), and [Cu-2(Diala4)(2)(DMSO)(2)]center dot 2 DMSO-2 acetone (12a) have 1D hydrogen-bonded polymeric structures while 4 has a 3D hydrogen-bonded network structure. Complex 8 displays a 2D coordination polymeric network structure. The complexes 1-13 have been investigated as functional models for the catechol oxidase by employing 3,5-di-tert-butylcatechol as a model substrate. Electron-withdrawing substituents reduced the activity while electron-donating substituents enhanced the activity. Variable-temperature magnetic studies conducted on compound 8 suggest the presence of strong inter-dimer antiferromagnetic coupling.