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Three new Complexes of Copper(II) with 1-Aminocyclopropane-1-Carboxylic Acid

Although the kinetic stabilities of isomeric cis- and trans-forms of bis(N, O-aminoacidato)copper(II) complexes are expected to be the same in aqueous solution, the crystallization process preferably gives rise to solids composed of only one isomer. Recently, we have succeeded to crystallise a trinuclear chelate complex from an aqueous solution containing Cu(II) ions and the ligand 1-aminocyclopropane-1-carboxylic acid (acc) that unexpectedly exhibited both structural isomers, [cis-Cu(acc)2]2[trans-Cu(acc)2(H2O)2](H2O)2. [Judaš, N. ; Raos, N. Inorg. Chem. 2006, 45, 4892-4894]. Further experiments with this unusual compound have yielded an acetic acid solvate of the trimer (I) ; [cis-Cu(acc)2]2[trans-Cu(acc)2(H2O)2](H2O)(AcOH), a hydrated cocrystal of urea and a monomeric trans-Cu(acc)2(urea) complex (II) ; [trans-Cu(acc)2(urea)](urea)(H2O) and a monomeric cis-Cu(acc)2(H2O) complex (III) ; [cis-Cu(acc)2(H2O)]. In the crystal phase of I trimeric moieties are cross-linked by an extensive system of hydrogen bonds. In this way, the trimeric building-blocks form a stable two-dimensional supramolecular architecture. Evaporation of a solution containing the starting Cu-acc complex and a large excess of urea provided crystals of II. In contrast to metal-organic trimers of I, the building blocks of II are mononuclear units with a single molecule of urea apically bonded to the central copper(II) atom. Hydrogen bonding through cocrystalized urea and bridging water molecules results with an material that may be best described as a hydrate of an organic-metalorganic cocrystal. Adding acetone to the aliquote of the mother liquor from which II was obtained provided crystals of III. The molecules of III are configurational isomers of II exhibiting geometry common to simple cis-copper(II) aminoacidato complexes with apically bonded water molecules.

Complexes of Copper(II); 1-Aminocyclopropane-1-Carboxylic Acid

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