Equilibrium and kinetic studies of complexes of the pendant donor macrocycles N,N',N'',N'''-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraazacyclododecane (THEC-12) and N,N',N'',N'''-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraazacyclopentadecane (THEC-15)

Abstract

Investigations of the thermodynamic and kinetic properties of the Co2+, Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+ complexes of N, N′, N″, N‴-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraazacyclododecane (THEC-12) and the newly synthesised N, N′, N″, N‴-tetrakis(2-hydroxyethyl)-1,4,8,12-tetraazacyclopentadecane (THEC-15) have been undertaken. Formation constants for the ML2+ complexes indicate that the hydroxyethyl groups cause significant destabilisation of the complexes with respect to those of the non-hydroxyethylated macrocycles. For decomplexation of [M(THEC-12)]2+ in aqueous HNO3 the observed rate constants =kobs = kO + kH[H+], where at 298.2 K, kO = (3.06 ± 1.86) × 10-5 s-1 when M Co, kO ≈ s-1 when M Ni and Cu, and 105 kH = 61.4 ± 2.9, 5.78 ± 1.42 and 2.81 ± 0.09 dm3 mol-1 s-1 when M Co, Ni and Cu, respectively. For [M(THEC-15)]2+, decomplexation is very slow with t 1 2>24 h (in 1.00 mol dm-3 HNO3) when M Co and Ni, but considerably faster with t 1 2 ≈ s (1.00 mol dm-3 HNO 3) when M Cu. © 1995.