Complexes of 1-thia-4,7,10-triazacyclododecane ([12]aneN(3)S) - Synthesis,structure and stability constants

The 12-membered macrocyclic ligand 1-thia-4,7, 10-triazacyclododecane ([12] aneN(3)S) has been synthesised, although upon crystallization from acetonit rile a product in which carbon dioxide had added to one secondary amine in the macrocyclic ring (H[12]aneN(3)SCO(2). H2O) was isolated and subsequentl y characterised by X-ray crystallography. The protonation constants for [12 ]aneN(3)S and stability constants with Zn(II), Pb(II), Cd(II) and Cu(II) ha ve been determined either potentiometrically or spectrophotometrically in a queous solution, and compared with those measured or reported for the ligan ds 1-oxa-4,7,10-triazacyclododecane ([12]aneN(3)O) and 1,4,7,10-tetraazacyc lododecane ([12]aneN(4)). The magnitudes of the stability constants are con sistent with trends observed previously for macrocyclic ligands as secondar y amine donors are replaced with oxygen and thioether donors although the s tability constant for the [Hg([12]aneN(4))](2+) complex has been estimated from an NMR experiment to be at least three orders of magnitude larger than reported previously. Zinc(II), mercury(II), lead(II), copper(II) and nicke l(II) complexes of [12]aneN(3)S have been isolated and characterised by X-r ay crystallography. In the case of copper(II), two complexes [Cu([12]aneN(3 )S)(H2O)](ClO4)(2) and [Cu-2([12]aneN(3)S)(2)(OH)(2)](ClO4)(2) were isolate d, depending on the conditions employed. Molecular mechanics calculations h ave been employed to investigate the relative metal ion size preferences of the [3333], asym-[2424] and sym-[2424] conformation isomers. The calculati ons predict that the asym-[2424] conformer is most stable for M-N bond leng ths in the range 2.00-2.25 Angstrom whilst for the larger metal ions the [3 333] conformer is dominant. The disorder seen in the structure of the [Zn([ 12]aneN(3)S)(NO3)](+) complex is also explained by the calculations. (C) 19 99 Elsevier Science Ltd. All rights reserved.