FULL PAPER DOI: 10.1002/ejic.201101433 Dinuclear Mn III Compounds [{Mn(bpy)(H 2 O)} 2 (μ-4-RC 6 H 4 COO) 2 - (μ-O)](NO 3 ) 2 (R = Me, F, CF 3 , MeO, tBu): Effect of the R Group on the Magnetic Properties and the Catalase Activity Montserrat Corbella,* [a] Gema Fernández, [a] Patricia González, [a] Miguel Maestro, [b] Mercè Font-Bardia, [c] and Helen Stoeckli-Evans [d] Keywords: Enzyme models / Magnetic properties / Manganese / Dinuclear compounds Five new dinuclear Mn III compounds [{Mn(bpy)(H 2 O)} 2 (μ-4- RC 6 H 4 COO) 2 (μ-O)](NO 3 ) 2 [R = Me (1), F (2), CF 3 (3), MeO (4) and tBu (5); bpy = 2,2'-bipyridine] have been synthesized; compounds 1–3 have been characterized by X-ray diffrac- tion. Moreover, a few crystals of the Mn III compound [{Mn(bpy)(H 2 O)}(μ-4-FC 6 H 4 COO)(μ-O){Mn(NO 3 )(bpy)(H 2 O)}]- (NO 3 ) 2 (6) have been obtained. Variable-temperature mag- netic susceptibility data of 1–5 were recorded; all compounds show ferromagnetic behaviour with J = 1.48 cm –1 for 1, 1.44 cm –1 for 2, 5.66 cm –1 for 3, 3.22 cm –1 for 4 and 2.68 cm –1 for 5 (H =–JS 1 ·S 2 ); and |D Mn | = 1.5 cm –1 and |E Mn | = 0.5 cm –1 for all compounds except for 2, for which these values are Introduction Interest in dinuclear Mn III complexes with carboxylato ligands is due to their presence in some metalloenzymes, such as Mn catalase, which is responsible for the dispropor- tionation of H 2 O 2 . [1] To mimic this enzyme, several dinu- clear Mn III complexes with a [Mn 2 (μ-O)(μ-RCOO) 2 ] 2+ core have been reported in the literature, [2–12] and in some cases, they have been magnetically and structurally charac- terized. [3–12] With this core, the hexacoordination of the Mn III ions could be acquired with tridentate blocking li- gands or with one bidentate and one monodentate ligand. Despite the magnetic interaction for this kind of compound [a] Departament de Química Inorgànica and Institut de Nanociència i Nanotecnologia (INIUB), Universitat de Barcelona, Martí i Franquès 1–11, 08028 Barcelona, Spain Fax: +34-934907725 E-mail: montse.corbella@ub.edu [b] Departamento de Química Fundamental and Servicios Xerais de Apoio a Investigación, Universidade da Coruña, 15071 A Coruña, Spain [c] Departamento de Cristallografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona, Martí i Franquès s/n, and Unitat de Difracció de RX, Serveis Científico-Tècnics, Universitat de Barcelona, Solé i Sabarís 1–3, 08028 Barcelona, Spain [d] Institut de Chimie, Université de Neuchâtel, Av. Bellevaux 51, 2007 Neuchâtel, Switzerland Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejic.201101433. Eur. J. Inorg. Chem. 2012, 2203–2212 © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2203 2.85 and 0.7 cm –1 , respectively. The coordination octahedron around the Mn III ions shows a rhombic distortion due to the coordination of a water molecule. This kind of distortion and the R group of the benzoato–derivative bridge in a para posi- tion favour ferromagnetic behaviour. Moreover, the presence of an electron-withdrawing substituent increases this mag- netic character. All compounds show catalase activity with a conversion range between 20 and 55 % of the initial H 2 O 2 within 10 min. Compounds 4, 5 and 3 with an electron-donat- ing R group are more efficient than 2, 3 with electron-with- drawing groups. being weak, the interest lies in the versatility of its magnetic behaviour and its relationship with structural parameters. In recent years we have focussed our attention on the study of the magnetic properties of dinuclear compounds with benzoato–derivative bridges [{Mn(NN)(L)} 2 (μ-O)(μ- RC 6 H 4 COO) 2 ] n+[6–12] and the analysis of the different fac- tors that modulate the magnetic interaction and whether it is ferro- or antiferromagnetic. One of these factors is the distortion around the manganese ions, [4,7,9–12] which is very sensitive to the monodentate ligand L, which could be H 2 O, NO 3 , ClO 4 , EtOH or N 3 . Moreover, the σ- or π-acid char- acter of this ligand [6,9] also has some effect on the magnetic behaviour. In compounds with 2-RC 6 H 4 COO bridges, the twist be- tween the phenyl ring and the COO group could be impor- tant and the degree of this torsion is crucial for the mag- netic interaction, as was reported for the two spinomers (S = 0 and 4) with formula [{Mn(H 2 O)(phen)} 2 (μ-2- ClC 6 H 4 COO) 2 (μ-O)](ClO 4 ) 2 . [10] This effect was also found for analogous compounds with ortho-benzoato–derivative bridges. [11] These kinds of compounds, with a labile position on the manganese(III) ions, are good candidates to test their effi- ciency to disproportionate H 2 O 2 . An increasing number of dinuclear Mn III compounds with catalase activity have been reported in the literature, [5,13–15] most of them with Schiff base ligands, and in some cases the catalytic cycle involves