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Issue 24, 2014
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The mechanism of the Cu2+[12-MCCu(Alaha)-4] metallacrown formation and lanthanum(III) encapsulation

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Abstract

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 α-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 Cu2(HL)22+ 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.

Graphical abstract: The mechanism of the Cu2+[12-MCCu(Alaha)-4] metallacrown formation and lanthanum(iii) encapsulation

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Publication details

The article was received on 21 Feb 2014, accepted on 28 Apr 2014 and first published on 29 Apr 2014


Article type: Paper
DOI: 10.1039/C4DT00557K
Citation: Dalton Trans., 2014,43, 9271-9282
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    The mechanism of the Cu2+[12-MCCu(Alaha)-4] metallacrown formation and lanthanum(III) encapsulation

    M. R. Beccia, B. García, J. García-Tojal, J. M. Leal, F. Secco and M. Tegoni, Dalton Trans., 2014, 43, 9271
    DOI: 10.1039/C4DT00557K

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