Comparative investigation of the interaction of Zn(II), Cd(II), Ag(I) and Pb(II) with dibenzo-substituted macrocyclic ligands incorporating both symmetrically and unsymmetrically arranged N, O and S donors : synthetic, solution and X-ray studies

A comparison of the interaction of Zn(II), Cd(II), Ag(I) and Pb(II) with a matrix of 18, 17-membered, dibenzo-substituted macrocyclic ligands (1-18) incorporating nitrogen, oxygen and/or sulfur heteroatom sites that share the same carbon backbone is reported. Potentiometric log K data for complexes of these metals with 5, 6, 8 and 9 incorporating unsymmetric arrangements of their donor sets were obtained and the results compared with previously determined stability data for the remaining symmetrical and unsymmetrical ligand complexes forming the above matrix. Structure-function relationships underlying the relative magnitudes of the respective log K values are discussed, with emphasis given to the influence of both the donor atom set and the donor atom sequence on the nature of the resulting complexes. The X-ray structures of [CdL(NO3)] (NO3)·CH3CH2OH (L = 4, SN4 donor set), [CdL(NO3)2]·CH3OH (L = 7, ON4 donor set), [AgL]PF6 (L = 4, SN4 donor set) and [AgL]PF6 (L = 9, OSN3 donor set) are presented along with that of the metal-free diprotonated nitrate salt (LH2)(NO3)2 (L = 6, S2N3 donor set).