Pentacopper(II) 12-metallacrown-4 complexes with α- and β-aminohydroxamic acids in aqueous solution: a reinvestigation

Synthesis, Solution Thermodynamics, and X‐ray Study of CuII [12]Metallacrown‐4 with GABA Hydroxamic Acid: An Unprecedented Crystal Structure of a [12]MC‐4 with a γ‐Aminohydroxamate

“…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 g-aminohydroxamic acid, fully supports the structural features interpreted from the thermodynamic data.…”

“…Thus, topological analogues of [12]crown-4 ligands ( [12]C-4) can be constructed, for example, by replacing the two methylene groups of each macrocycle arm with À M À N À coordination units (Scheme 1 and ref. [1]).…”

“…This structure, called [12]metallacrown-4 ( [12]MC-4), is a 12-membered macrocycle capable of encapsulating a core metal ion into a four-oxygenatom cavity. While [12]MC-4 complexes generally contain Cu 2 + as a core cation, [1,7,8] for [15]MC-5 complexes, the fiveoxygen cavity is of suitable dimensions to encapsulate lanthanideA C H T U N G T R E N N U N G (III), [9] calcium(II), [10] or uranyl(II) ions. [10] Abstract: The solution equilibria of gaminobutanehydroxamic acid (GABAha) with H + and Cu 2 + were investigated by potentiometry, titration calorimetry, spectrophotometry, NMR spectroscopy, and ESI-MS.…”

“…[10] Abstract: The solution equilibria of gaminobutanehydroxamic 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)-aAlaha and b-Alaha. The stability (ÀDG 0 ) sequence was b-Alaha @ aAlaha > GABAha, whereas the order of formation enthalpies (ÀDH 0 ) was bAlaha @ GABAha > a-Alaha.…”

“…[1] The structures of [12]metallacrown-4 and [15]metallacrown-5 complexes with b-and aaminohydroxamates are presented in Scheme 2. Notably, Cu II metallacrowns are only structural, and not functional, analogues of the parent organic compounds, because vacant metallacrowns (with no metal ions in the cavity ) have not yet been isolated.…”