Manganese compounds with phthalate and terephthalate ligands: Synthesis, crystal structure, magnetic properties and catalase activity

Abstract

The reactivity of carboxybenzoic acids substituted in ortho, meta and para positions (phthalic, isophthalic and terephthalic acids) has been explored. These acids have been used for the synthesis of dinuclear Mn III and polynuclear Mn II compounds, obtaining unexpected results. From all the reactions, one dinuclear Mn III compound, [{Mn(H 2O)(phen)} 2(μ-2-COOHC 6H 4COO) 2(μ-O)](ClO 4) 2 (1), one mixed valence compound, [{Mn(phen) 2} 2(μ-O) 2](NO 3) 3 (2), and four Mn II compounds, [{Mn(H 2O)(phen) 2} 2(μ-4-COOC 6H 4COO)](NO 3) 2 (3), [Mn 3(μ-4- COOC 6H 4COO) 3(bpy) 2] n (4), [{Mn(phen) 2} 2(μ-2-COOHC 6H 4COO) 2](ClO 4) 2 (5) and [Mn(μ-2-COOC 6H 4COO)(H 2O) 2(phen)] n (6), (phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine) have been obtained and characterised by X-ray diffraction, showing different coordination modes for the carboxylate ligand: a bidentate bridge in a syn-syn, syn-anti or anti-anti mode, a bis-monodentate bridge and a bis-bidentate bridge. The six compounds show antiferromagnetic coupling, with magnetic interaction constants of -3.7 and -332.5 cm -1 for the dinuclear Mn III (1) and Mn IIIMn IV (2) compounds and -0.04, -4.5, -1.5 and -0.55 cm -1 for Mn II compounds 4-6. Each Mn II compound shows a different EPR spectrum at 4 K, which has been simulated including the ZFS parameters. The catalase activity of the compounds with phthalate and terephthalate ligands has been studied, the former being less active than the latter. © 2012 Elsevier Ltd. All rights reserved.