摘要:

The chelate, macrocyclic, and cryptate effects are analyzed. It is concluded that for all three effects considerable stabilization is derived from the greater basicity induced in donor atoms as ethylene bridges are added. Further considerations of importance in these effects are (1) desolvation effects, where steric constraints to solvation of the donor atoms in the free ligand lead to increased complex stability, (2) enforced dipole-dipole repulsion in the ligand, which is relieved on complex formation, and (3) structural preorganization of the ligand such that the donor atoms in the free ligand are already correctly oriented for complex formation. Only for the chelate effect is entropy of paramount importance, where it is derived from a cratic effect. It is emphasized that the level of preorganization of macrocycles, and to a lesser extent cryptands, is much lower than commonly realized. Newly emerging types of more highly preorganized ligands are discussed.

ISSN:0260-3594    

DOI:10.1080/02603598808072293

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

That in a metal-ion chelate one binding site may be more weakly bound than another is often expected, though it is not equally well realized that such differences in metal-ion affinities may give rise to intramolecular equilibria between open and closed, i.e. chelated, forms. Quantification procedures for such equilibria are outlined and applied to describe the situation in complexes of N-substituted iminodiacetate and α-substituted acetate ligands. Corresponding procedures are applicable to the characterization of intramolecular ligand-ligand interactions in mixed ligand complexes. Isomerization equilibria are of general importance; e.g. in metal-ion catalyzed or facilitated technical or biological processes.

ISSN:0260-3594    

DOI:10.1080/02603598808072294

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0260-3594    

DOI:10.1080/02603598808072292

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor