Ioana M. Vasilescu

Metal-ion recognition. Modeling the stability constants of some mixed-donor macrocyclic metal ion complexes—a simple model

A procedure for modeling the stability constants of the Zn(II), Cd(II), Ag(I) and Pb(II) complexes of an extended series of 17-membered, mixed-donor macrocycles incorporating nitrogen, oxygen and/or sulfur donor atoms is presented. The ligands fall into two categories—those incorporating a symmetrical arrangement of their donor atom set (9 examples) and those in which the donor set has an unsymmetrical arrangement (5 examples). Metal stability constants for the former have been reported previously while corresponding data for the latter was determined as part of the present investigation. Initial computations were based on the 1:1 stability constants for the systems incorporating a symmetrical arrangement of their donor atom set. The approach employed was to assume that the overall free energy for metal complexation can be partitioned into the sum of contributions from individual metal–donor interactions. Thus for a given metal ion type, the log K data corresponding to each of these ligand systems were employed to derive parameters that are characteristic of the respective metal ion–donor bond types present. The parameterisation derived from the above (previously reported) stability data was then employed to compute log K values for the complexes of both the symmetrical and unsymmetrical ligand series. In general, quite good agreement with the experimentally determined log K values for both series of complexes was obtained. The procedure thus points the way for the prediction of metal complex stabilities for other systems that incorporate closely related ligand types.

New macrocyclic ligands: XIV. synthesis and X-ray structures of potentially pentadentate ligands incorporating non-symmetrically arranged N4S-, N3OS-, N2O2S- and N2S2O-heteroatoms

The synthesis and characterization of new mixed-donor macrocyclic ligands incorporating nitrogen, sulfur and/or oxygen heteroatoms are described. The new 17- or 18-membered macrocyclic rings contain unsymmetrical arrangements of their heteroatoms in contrast to related, previously reported rings in which the donor sets are arranged symmetrically. The X-ray structures of the 17-membered rings incorporating N4O- and N4S-donor sets are presented.

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).