The preparation, characterization and solution chemistry of some nickel(II) and copper(II) complexes of 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane

Abstract

The preparation of the new ligand 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane, (-N(Me)-(CH₂)_2-)₄ (= L), and the complexes [NiL] (ClO₄)₂, [NiL(OCHNMe₂)] (ClO₄)₂, [NiLN₃] ClO₄, [CuL] (ClO₄)₂, and [NiY] (ClO₄)₂, where Y = (-N(Me)(CH₂)₂N(Me)(CH₂)_3-)₂, 1,4,8,11-tetra-methyl-1,4,8,11-tetraazacyclotetradecane, are described. The magnetic moments of the nickel((11) species are reported, and the labile low-spin/high spin equilibria characterizing the [NiLI²⁺ and [NiY]²⁺ systems over a range of temperatures and ionic strengths in aqueous solution are discussed. The spectrophotometric titration of the aqua ligands in [NiLH₂O]²⁺, [CuLH₂O]²⁺, and [NiYH₂O]²⁺ against sodium hydroxide yields pK_a values of 10.2 ± 0.2, 12.0 ± 0.3 and 10.7 ± 0.2, respectively, and a study, using Job's method of continuous variations, of the formation of azide species shows [NiLN₃]⁺ and [NiYN₃]⁺ to be formed predominantly in aqueous solution.