Cadmium(II) complexation by a series of triazacycloalkanes ([ x]aneN 3, x = 9–12). An equilibrium and structural study

Abstract

The complexation of Cd(II) by a series of triazacycloalkanes, ([ x]aneN 3, x = 9–12), has been studied in 0.10 mol dm −3 KNO 3 aqueous solution at 298.2±0.1 K. Stabillitoy constants ( β CdL) for the complexes decrease in magnitude with increasing number of atoms in theligand ring, and are several orders of magnitude smaller than corresponding β ZnL values. Two complexes [Cd 2([9]aneN 3) 2(μ-Cl) 2Cl 2] ( 1) and [Cd 2([11]aneN 3) 2(μ-Cl) 2Br 2] ( 2) were synthesized, and the structures determined by X-ray crystallography. Complex 1 crystallizes in the triclinic space group P1, with a = 7.657(2), b = 7.741(2), c = 17.750(2) A ̊ , α = 90.13(3), β = 94.65(3), γ = 90.76(3)° and V = 1048.5(5) A ̊ 3 for Z = 2 . Complex 2 crystallizes in the monoclinic space group P2 1 c with a = 8.144(2), b = 8.469(2), c = 18.480(4) A ̊ , β = 97.62(3)° and V = 1263.3(6) A ̊ 3 for Z = 2 . Both structures contain bridging di-μ-chloro groups separating six-coordinate Cd(II). Each Cd(II) is also bonded to a tridentate ligand and Cl (structure 1) or Br (structure 2).