N-benzoylated 1,4,8,11-tetraazacyclotetradecane and their copper(II) and nickel(II) complexes: spectral, magnetic, electrochemical, crystal structure, catalytic and antimicrobial studies.

A series of N-benzoylated cyclam ligands incorporating three different benzoyl groups 1,4,8,11-tetra-(benzoyl)-1,4,8,11-tetraazacyclotetradecane (L(1)), 1,4,8,11-tetra-(2-nitrobenzoyl)-1,4,8,11-tetraazacyclotetradecane (L(2)) and 1,4,8,11-tetra-(4-nitrobenzoyl)-1,4,8,11-tetraazacyclotetradecane (L(3)) and their nickel(II) and copper(II) complexes are described. Crystal structure of L(1) is also reported. The ligands and complexes were characterized by elemental analysis, electronic, IR, (1)H NMR and (13)C NMR spectral studies. N-benzoylation causes red shift in the lambda(max) values of the complexes. The cyclic voltammogram of the complexes of ligand L(1) show one-electron, quasi-reversible reduction wave in the region -1.00 to -1.04 V, whereas that of L(2) and L(3) show two quasi-reversible reduction peaks. Nickel complexes show one-electron quasi-reversible oxidation wave at a positive potential in the range +1.05 to +1.15 V. The ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry with nuclear hyperfine spin 3/2. All copper(II) complexes show a normal room temperature magnetic moment values mu(eff) 1.70-1.73 BM which is close to the spin-only value of 1.73 BM. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts and hydrolysis of 4-nitrophenylphosphate using the copper(II) and nickel(II) complexes as catalysts were carried out. All the ligands and their complexes were also screened for antimicrobial activity against Gram-positive, Gram-negative bacteria and human pathogenic fungi.