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)-1,4,8,12-TETRAAZACYCLOPENTADECANE (THEC-15)

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 ML(2+) 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=k(obs)=k(0)+k(H)[H+], where at 298.2 K, k(0)=(3.06+/-1.86)x10(-5) s(-1) when M=Co, k(0) approximate to 0 s(-1) when M= Ni and Cu, and 10(5) k(H)=61.4+/-2.9, 5.78+/-1.42 and 2.81+/-0.09 dm(3) 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)approximate to 18 s (1.00 mol dm(-3) HNO3) when M-Cu.