Agnieszka Dobosz

A new Cu(II) [12]metallocrown-4 pentanuclear complex based on a Cu (II ) -malonomonohydroxamic acid unit

The first example of a Cu(II) [12]-MC-4 hydroxamic metallacrown compound containing a carboxyl group as a supporting donor function is described. The solution equilibria of malonomonohydroxamic acid (MACZ, H2L) with Cu(II) are investigated in aqueous solution using a combination of potentiometry, UV-vis absorption spectrophotometry, EPR spectroscopy and ESI mass spectrometry. Among the four complexes fitting the best speciation model ([CuL], [Cu5L4H−4]2−, [CuL2]2− and [CuL2H−1]3−), a pentameric metallacrown molecule of composition Cu : L = 5 : 4 predominates in solution over the pH 4 to 11 range, and the corresponding complex was isolated in the solid state. The crystallization of the complex [Cu5L4H−4]2− in the presence of [Cu(en)2(H2O)2]2+ cations resulted in the isolation of [Cu(en)2(H2O)2]n[Cu(en)2(H2O)(μ-H2O){Cu5(L4H−4)(H2O)3}2]n·20nH2O (1), whose crystal structure has been determined by X-ray analysis. The structure of 1 consists of centrosymmetric complex cations [Cu(en)2(H2O)2]2+, infinite complex anionic chains [Cu(en)2(H2O)(μ-H2O){Cu5(L4H−4)(H2O)3}2]n2n− and solvate water molecules. Within the complex anionic chains, the decanuclear double-decked bis([12]-MC-4) complex anions {Cu5(L4H−4)(H2O)3}24− are united by the [Cu(en)2(H2O)2]2+ complex cations due to the bridging function of the axial water molecule O(5). The magnetic behaviour of 1, studied in the temperature range 1.8–300 K, suggests the presence of both antiferromagnetic and ferromagnetic contributions to the observed magnetic susceptibility, resulting in a ground state of S = 2 per formula unit.

Pyridine-2,6-dihydroxamic acid, a powerful dihydroxamate ligand for Ni2+ and Cu2+ ions

Pyridine-2,6-dihydroxamic acid was found to be the most effective ligand for Ni2+ and Cu2+ ions among the known dihydroxamates. The stability constants of the title complexes are many orders of magnitude higher than those obtained for the other dihydroxamates. Only equimolar species are formed with Cu2+ ions, while NiL and bis-complexes are formed in the case of Ni2+. The [NiL2]2− complex anion contains compressed octahedral hexanitrogen surroundings of two meridionally coordinated ligands. The equatorial Ni–N(Py) bonds are significantly shorter than the axial Ni–N(hydroxamate) distances although the latter are formed by the deprotonated groups.

Coordination of thiouridine monophosphates with selected metal ions.

Potentiometric and spectroscopic data obtained for the complexes of two thio-substituted uridine-monophosphates with Cu(2+), Ni(2+) and Cd(2+) ions have shown that both thionucleotide are more effective ligands than their nucleoside analogues. The basic binding site for all metal ions is the sulfur atom. The chelation by adjacent N(3) donor is also likely, although unfavorable four-membered chelate ring is formed.

Copper(II) and nickel(II) complexes with oxime analogues of amino acids. Potentiometric, spectroscopic and X-ray studies of complexes with 2-cyano-2-(hydroxyimino)acetic acid and its ethane-1,2-diamine derivative

2-Cyano-2-(hydroxyimino)acetic acid was found to be an effective ligand for Cu2+ and Ni2+ ions over a very broad pH range. Potentiometric and spectroscopic data indicate the formation of dimeric complexes with Cu2+ ions and the first X-ray evidence for dimer formation is obtained. Conjugation of the oximic moiety with ethane-1,2-diamine leads to another very effective family of chelating agents, although metal ion co-ordination may induce amide bond hydrolysis as indicated by the crystal structure.

Insertion of oximic and hydroxamic functions into one simple amino acid creates a new family of powerful chelating agents

2-(Hydroxyimino)propanohydroxamic acid, a derivative of alanine in which the amino group has been transformed into oxime and the carboxylic group into a hydroxamic function, is a more powerful chelating agent for Cu2+ and Ni2+ ions than alanine itself, its oximic or hydroxamic analogues.