New 14-membered trans-di-substituted ‘tet-a’ macrocycles and their copper(II) and nickel(II) complexes: Spectral, magnetic, electrochemical, crystal structure, catalytic and antimicrobial studies

Copper(II) and nickel(II) complexes of new trans-di-substituted macrocyclic ligands incorporating three different benzoyl groups, 1,8-bis-(benzoyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L1), 1,8-bis-(2-nitrobenzoyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L2), and 1,8-bis-(4-nitrobenzoyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L3) have been synthesized. The ligands and complexes were characterized by elemental and spectral analysis. Further, the X-ray crystal structure of one of the ligand, L1, has been determined. N-benzoylation causes red shift in the λmax values of the complexes. The cyclic voltammogram of the complexes of ligand L1 shows one-electron, quasi-reversible reduction wave in the region −0.94 to −1.00 V, whereas that of L2 and L3 show two quasi-reversible reduction peaks corresponding to ligand and metal. Nickel complexes show one electron quasi-reversible oxidation wave at a positive potential in the range +0.92 to +1.21 V. The Cu(II) complexes have a magnetic moment value close to the spin-only value with four hyperfine EPR signals. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts and on the hydrolysis of 4-nitrophenylphosphate using the copper(II) and nickel(II) complexes as catalysts were carried out. The complexes containing electron-withdrawing group shows higher rate-constant values than that with no electron-withdrawing group. All the complexes were screened for antifungal and antibacterial activity.