The complex-formation equilibria of the system Ni(II)/β-alaninehydroxamic acid (β-AlaHA, LH) have been studied in solution by using potentiometry, calorimetry, ESI mass spectrometry and UV-Visible spectrophotometry. A series of mononuclear and polynuclear species have been identified at different pH and for different Ni(II)/ligand ratios. Among the polymetallic species, we have identified the 12-metallacrown-4 (12-MC-4) species [Ni5(LHâ1)4]2+, which is analogous to the previously characterized [Cu5(LHâ1)4]2+ 12-MC-4 complex, and which corresponds to the metallacrown complex predicted by the Metallacrown Structural Paradigm. Besides this species, we have very unexpectedly identified in solution three other polynuclear species, corresponding to the stoichiometries [Ni4(LHâ1)4], [Ni5(LHâ1)5] and [Ni6(LHâ1)6]. A metallacrown with the same stoichiometry as [Ni5(LHâ1)5] containing α-AlaHA as the ligand has been previously reported, while the other two species are new for the speciation systems of Cu(II) or Ni(II) aminohydroxamic acids. Intriguingly, all the three latter stoichiometries correspond to those of vacant 12-MC-4, 15-MC-5 or 18-MC-6 species. The thermodynamic parameters related to their formation in solution are discussed, together with the speciation of the mononuclear complexes, on the basis of the structural and thermodynamic information available on metallacrowns.
通过电位法、热量法、电喷雾质谱法和紫外可见分光光度法,对Ni(II)/
β-丙氨酸羟
肟酸(β-AlaHA,LH)系统的复杂平衡进行了研究。在不同pH值和不同Ni(II)/
配体比下,确定了一系列单核和多核物种。在多
金属物种中,我们确定了12-
金属冠-4(12-MC-4)物种[Ni5(LH≠1)4]2+,它与之前鉴定的[Cu5(LH≠1)4]2+ 12-MC-4复合物类似,与
金属冠结构范式预测的
金属冠复合物相对应。除了这个物种,我们还意外地在溶液中发现了其他三个多核物种,它们与
化学计量比[Ni4(LH≠1)4]、[Ni5(LH≠1)5]和[Ni6(LH≠1)6]相对应。之前有报道过一种与[Ni5(LH≠1)5]具有相同
化学计量比的
金属冠,其中包含作为
配体的
β-丙氨酸羟
肟酸,而其他两种物种对于Cu(II)或Ni(II)
氨基羟
肟酸的物种系统来说是新的。有趣的是,后三种
化学计量比都与空12