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

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posted on 1996-11-06, 00:00 authored by Hirotaka Nagao, Nobutoshi Komeda, Masao Mukaida, Masatatsu Suzuki, Koji Tanaka
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 (Me1tpa), bis((6-methyl-2-pyridyl)methyl)(2-pyridylmethyl)amine (Me2tpa), and tris((6-methyl-2-pyridyl)methyl)amine (Me3tpa), have been synthesized and characterized by X-ray crystallography. [Cu(H2O)(tpa)](ClO4)2 (1) crystallized in the monoclinic system, space group P21/a, with a = 15.029(7) Å, b = 9.268(2) Å, c = 17.948(5) Å, β = 113.80(3)°, and Z = 4 (R = 0.061, Rw = 0.059). [CuCl(Me1tpa)]ClO4 (2) crystallized in the triclinic system, space group P1̄, with a = 13.617(4) Å, b = 14.532(4) Å, c = 12.357(4) Å, α = 106.01(3)°, β = 111.96(2)°, γ = 71.61(2)°, and Z = 4 (R = 0.054, Rw = 0.037). [CuCl(Me2tpa)]ClO4 (3) crystallized in the monoclinic system, space group P21/n, with a = 19.650(4) Å, b = 13.528(4) Å, c = 8.55(1) Å, β = 101.51(5)°, and Z = 4 (R = 0.071, Rw = 0.050). [CuCl(Me3tpa)][CuCl2(Me3tpa)]ClO4 (4) crystallized in the monoclinic system, space group P21/a, with a = 15.698(6) Å, b = 14.687(7) Å, c = 19.475(4) Å, β = 97.13(2)°, and Z = 4 (R = 0.054, Rw = 0.038). All the Cu atoms of 14 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 Me1tpa, Me2tpa, and Me3tpa complexes with only oxygen atom to form nitrito adducts. The cyclic voltammograms of [Cu(H2O)(Mentpa)]2+ (n = 0, 1, 2, and 3) in the presence of NO2- in H2O (pH 7.0) revealed that the catalytic activity for the reduction of NO2- increases in the order Me3tpa ≪ Me2tpa ≪ Me1tpa < tpa complexes.

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