COMPLEXATION OF COBALT(II), NICKEL(II) AND COPPER(II) BY THE PENDANT ARM MACROCYCLIC LIGAND (2-HYDROXYETHYL)-1,4,8,11-TETRAAZACYCLOTETRADECANE

A stopped-flow spectrophotometric study of the complexation of Co2+ an d Ni2+ by the pendant arm ligand, N, N', N, (2-hydroxyethyl)-1,4,8,11- tetraazacyclotetradecane (L2), in aqueous solution at pH 6.80, I = 1.5 0 (NaNO3) and 298.2 K yields the rate constants, k(LH') = 880 and 116 dm3 mol-1 s-1 for the complexation of Co2+ and Ni2+, respectively, by the monoprotonated ligand, L2H+. In aqueous HNO3, the decomplexation o f [ML2]2+ is characterized by: k(obs) = k0 + k1K1a[H+]/1 + K1a[H+] whe re at 298.2 K, k0 = 0.21, almost-equal-to 0 and almost-equal-to 0 s-1, k1 = 151, 0.160 and 6.07 s-1, and K1a = 5.2, 83 and 0.67 dm3 mol-1, r espectively, when M2+ = Co2+, Ni2+ and Cu2+. The effect of the pendant arms on the complexation and decomplexation processes are considered through a comparison of these data with those for 1,4,8,11-tetraazacyc lotetradecane and related ligands.