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Synthesis, Solution Thermodynamics, and X-ray Study of Cu(II) [12]Metallacrown-4 with GABA Hydroxamic Acid: An Unprecedented Crystal Structure of a [12]MC-4 with a gamma-Aminohydroxamate.

Tegoni M, Ferretti L, Sansone F, Remelli M, Bertolasi V, Dallavalle F

Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Università degli Studi di Parma, Viale G.P. Usberti 17A, 43100 Parma, Italy, Fax: (+39) 0521-905-557.

The solution equilibria of gamma-aminobutanehydroxamic acid (GABAha) with H(+) and Cu(2+) were investigated by potentiometry, titration calorimetry, spectrophotometry, NMR spectroscopy, and ESI-MS. The thermodynamic parameters of the Cu(II) [12]metallacrown-4 obtained for GABAha were compared with those of the corresponding complexes of (S)-alpha-Alaha and beta-Alaha. The stability (-DeltaG(0)) sequence was beta-Alaha>>alpha-Alaha>GABAha, whereas the order of formation enthalpies (-DeltaH(0)) was beta-Alaha>>GABAha>alpha-Alaha. These data were interpreted on the basis of the dimensions of the chelate rings and the planarity of the metallamacrocycles. The Cu(II) [12]metallacrown-4 ([12]MC-4) complex of GABAha was isolated and its crystal structure, which is the first reported for a [12]MC-4 of a gamma-aminohydroxamic acid, fully supports the structural features interpreted from the thermodynamic data.

Published 17 January 2007 in Chemistry, 13(4): 1300-1308.
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