Synthesis and Characterization of New trans N , N ′-Disubstituted Macrocyclic “tet a ” Ligands and Their Copper(II) and Nickel(II) Complexes: Structural, Electrochemical, Magnetic, and Catalytic Studies

New trans-disubstituted macrocyclic ligands (L 1 ), trans-1,8-[N,N'-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}]-1,4,8,11-tetraaza-5,5,7,12,12,14-hexamethylcyclotetradecane, and (L 2 ), 1,8-[N,N'-bis{(3-formyl-2-hydroxy-5-methyl)-benzyl}]-4,11-dimethyl-1,4,8,11-tetraaza-5,5,7,12,12,14-hexamethylcyclotetradecane, were synthesized. The ligands were characterized by elemental analysis, IR, 1 H and 1 3 C NMR spectral analyses. The ligand L 1 crystallized as monoclinic in the space group P2 1 /n, and the final R-value was found to be 0.062. Copper(II) and nickel(ll) complexes of these ligands were prepared and characterized by elemental analysis, IR, UV-visible, FAB-mass spectral studies. Electrochemical studies of the nickel(II) complexes show one-electron quasireversible reduction around -1.00 to -1.13 V and one-electron quasireversible oxidation around 1.00 to 1.14 V. The copper(II) complexes show one-electron quasireversible reduction around -0.93 to -1.10 V. ESR spectral studies of the copper(II) complexes show hyperfine splitting with a g∥ value of 2.31, a g⊥ value of around 2.02 and an A value of 160 G. The magnetic moment values (μ e f f ) of the Cu(II) complexes fall in the range of 1.71 to 1.72 B.M. at room temperature (298 K). The rate-constant values of the catalytic hydrolysis of p-nitrophenyl phosphate for the copper(II) complexes were in the range 6.3 x 10 - 3 to 12.2 x 10 - 3 min - 1 and for the nickel(II) complexes in the range 10 x 10 - 3 to 14 x 10 - 3 min - 1 . The rate-constant values of the catalytic oxidation of catechol to o-quinone were in the range 9.4 x 10 - 3 to 13.4 x 10 - 3 min - 1 for the copper(II) complexes. The copper(II) and nickel(II) complexes of ligand L 2 have higher catalytic activity than that of ligand L 1 .