期刊
DALTON TRANSACTIONS
卷 43, 期 24, 页码 9271-9282出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c4dt00557k
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资金
- Obra Social la Caixa [OSCL-2012-007]
- Ministerio de Ciencia e Innovacion [CTQ2010-15358]
- Junta de Castilla y Leon [BU237U13, BU-299A12-1]
A kinetic, calorimetric, mass spectrometry and EPR study has been performed on the formation of the metallacrown Cu2+[12-MCCu(Alaha)-4] from Cu(II) and alpha-alaninehydroxamic acid (H2L). The acidity range where Cu2+[12-MCCu(Alaha)-4] is stable lies between pH 3.5 and 6.0. For pH values below that range the complex CuHL+ is the prevailing species. This species plays a fundamental role in the formation of Cu2+[12-MCCu(Alaha)-4]. Actually, depending on the Cu(II)/H2L ratio and on pH, it can originate a dimer Cu-2(HL)(2)(2+) or a dinuclear complex Cu2L2+. Both species constitute the nuclei necessary for a further oligomerisation reaction which ends when the crown is formed. The kinetics of Cu2+[12-MCCu(Alaha)-4] formation is biphasic. Under conditions of Cu(II) excess the fast phase leads to formation of Cu2L2+. The slow phase is interpreted in terms of a sequential addition of monomers (CuHL+) to the Cu2L2+ nucleus to form the crown. The interaction of La(III) with Cu2+[12-MCCu(Alaha)-4] has also been investigated. The system displays a biphasic behaviour; in the first phase the intermediate complex Cu[12-MCCu(Alaha)-4] La is formed which, in excess of ligand, evolves towards the larger metallacrown La3+[15-MCCu(Alaha)-5]. The reaction mechanisms of the two investigated systems are discussed.
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