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Issue 21, 2015
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Synthesis of mixed-valence hexanuclear Mn(II/III) clusters from its Mn(II) precursor: variations of catecholase-like activity and magnetic coupling

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Abstract

One Mn(II) coordination polymer, [Mn(o-(NO2)C6H4COO)2(pyz)(H2O)]n (1), has been synthesized and oxidized with n-Bu4NMnO4 in non-aqueous media to two mixed-valence hexanuclear Mn(II/III) complexes [MnIII2MnII4O2(pyz)0.61/(MeOH)0.39(o-(NO2)C6H4COO)10·(H2O)·{(CH3)2CO}2]·(CH3)2CO (2) and [MnIII2MnII4O2(pyz)0.28/(MeCN)3.72(o-(NO2)C6H4COO)10·(H2O)] (3) (where pyz = pyrazine). All three complexes were characterized by elemental analyses, IR spectroscopy, single-crystal X-ray diffraction analyses, and variable-temperature magnetic measurements. The structural analyses reveal that complex 1 is comprised of linear chains of pyz bridged Mn(II), which are further linked to one another by synanti carboxylate bridges, giving rise to a two-dimensional (2D) net. Complexes 2 and 3 feature mixed valence [MnIII2MnII4] units in which each of the six manganese centres reside in an octahedral environment. Apart from the variations in terminal ligands (acetone for 2 and acetonitrile for 3), the complexes are very similar. Using 3,5-di-tert-butyl catechol (3,5-DTBC) as the substrate, the catecholase-like activity of the complexes has been studied and it is found that the mixed valent Mn6 complexes (2 and 3) are much more active towards aerial oxidation of catechol compared to the Mn(II) complex (1). Variable-temperature (1.8–300 K) magnetic susceptibility measurements showed the presence of antiferromagnetic coupling in all three complexes. The magnetic data have been fitted with a 2D quadratic model derived by Lines, giving the exchange constant J/kB = −0.0788(5) K for 1. For 2 and 3, antiferromagnetic interactions within the Mn6 cluster have been fitted with models containing three exchange constants: JA/kB = −70 K, JB/kB = −0.5 K, JC/kB = −2.9 K for 2 and JA/kB = −60 K, JB/kB = −0.3 K, JC/kB = −2.8 K for 3.

Graphical abstract: Synthesis of mixed-valence hexanuclear Mn(ii/iii) clusters from its Mn(ii) precursor: variations of catecholase-like activity and magnetic coupling

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Publication details

The article was received on 17 Feb 2015, accepted on 16 Apr 2015 and first published on 16 Apr 2015


Article type: Paper
DOI: 10.1039/C5DT00709G
Author version available: Download Author version (PDF)
Citation: Dalton Trans., 2015,44, 9795-9804
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    Synthesis of mixed-valence hexanuclear Mn(II/III) clusters from its Mn(II) precursor: variations of catecholase-like activity and magnetic coupling

    P. Kar, Y. Ida, T. Kanetomo, M. G. B. Drew, T. Ishida and A. Ghosh, Dalton Trans., 2015, 44, 9795
    DOI: 10.1039/C5DT00709G

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