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1 2001

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Chemiczne i biochemiczne aspekty kompleksów mieszanych

Kroczewska D., Kurzak B.

Wiadomości Chemiczne

2001

[Z] 55, 3-4

263-287

During the last two decades thousands of important papers and some excelant review concerning complex equilibria have been published. In fact, most of these papers concern data on complex equilibrium, which does not involve species other than simple complexes with a completely homogenous coordination sphere Because mixed-ligand complexes are the most general and probable forms of existence of the elements in solution, we would like to present the mixed-ligand complexes in the aspect of their role in chemistry and in living systems. In the first part of this text we have lain particular emphasis upon literature data which show that it is worthwhile to assemble information on the formation, stability, structure and on the mutual influence of two ligands bound to the same metal ion, in the next part - on biochemical processes (transport, storage, inhibition of anzyme processes) which might be simulated by mixed-ligand complexes as "model systems" and at last - on own studies upon the mixed-ligand complexes of hydroxamic acid (a- or b-alaninehydroxamic acid) and one of polyamines with different metal ions. In order to find the answer for the following question: what kind of stoichiometry, geometry and binding mode there is in complexes which arrive in studied ternary systems? We used different methods: pH-metric method and spectroscopic ones (UV-VIS, EPR and NMR). The results obtained in our investigations and presented in this text show that the steric effect plays a very important role in the formation of the mixed-ligand complexes. In the case of bulky polyamine bonded in the zink(II) equimolar complex the coordination of a- or b-alaninehydroxamic acid is more favoured than the second polyamine ligand. There is no mixed-ligand complex formation in the case of ternary sestems with nickel(II). The reason for this is in the geometry of parent complexes - octahedral for nickel(II)-amine and square planar for nickel(II)-a-Alaha systems. The tridentate coordination of diethylenetriamine results in five-coordinated mixed-ligand copper(II) complexes in which the aminohydroxamate moiety adopts an equatorial-axial coordination mode.