Structural and Electrochemical Comparison of Copper(II) Complexes with Tripodal Ligands

A series of copper(II) complexes with tripodal polypyridylmethylamine ligands, such as tris(2-pyridylmethyl)amine (tpa), ((6-methyl-2-pyridyl)methyl)bis(2-pyridylmethyl)amine (Me(1)tpa), bis((6-methyl-2-pyridyl)methyl)(2-pyridylmethyl)amine (Me(2)tpa), and tris((6-methyl-2-pyridyl)methyl)amine (Me(3)tpa), have been synthesized and characterized by X-ray crystallography. Cu(H(2)O)(tpa)](ClO(4))(2) (1) crystallized in the monoclinic system, space group P2(1)/a, with a = 15.029(7) ?, b = 9.268(2) ?, c = 17.948(5) ?, beta = 113.80(3) degrees, and Z = 4 (R = 0.061, R(w) = 0.059). CuCl(Me(1)tpa)]ClO(4) (2) crystallized in the triclinic system, space group P&onemacr;, with a = 13.617(4) ?, b = 14.532(4) ?, c = 12.357(4) ?, alpha = 106.01(3) degrees, beta = 111.96(2) degrees, gamma = 71.61(2) degrees, and Z = 4 (R = 0.054, R(w) = 0.037). CuCl(Me(2)tpa)]ClO(4) (3) crystallized in the monoclinic system, space group P2(1)/n, with a = 19.650(4) ?, b = 13.528(4) ?, c = 8.55(1) ?, beta = 101.51(5) degrees, and Z = 4 (R = 0.071, R(w) = 0.050). CuCl(Me(3)tpa)]CuCl(2)(Me(3)tpa)]ClO(4) (4) crystallized in the monoclinic system, space group P2(1)/a, with a = 15.698(6) ?, b = 14.687(7) ?, c = 19.475(4) ?, beta = 97.13(2) degrees, and Z = 4 (R = 0.054, R(w) = 0.038). All the Cu atoms of 1-4 have pentacoordinate geometries with three pyridyl and one tertiary amino nitrogen atoms, and a chloride or aqua oxygen atom. Nitrite ion coordinated to the Cu(II) center of Me(1)tpa, Me(2)tpa, and Me(3)tpa complexes with only oxygen atom to form nitrito adducts. The cyclic voltammograms of Cu(H(2)O)(Me(n)()tpa)](2+) (n = 0, 1, 2, and 3) in the presence of NO(2)(-) in H(2)O (pH 7.0) revealed that the catalytic activity for the reduction of NO(2)(-) increases in the order Me(3)tpa < Me(2)tpa < Me(1)tpa < tpa complexes.