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

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 MnIII and polynuclear MnII compounds, obtaining unexpected results. From all the reactions, one dinuclear MnIII compound, [{Mn(H2O)(phen)}2(μ-2-COOHC6H4COO)2(μ-O)](ClO4)2 (1), one mixed valence compound, [{Mn(phen)2}2(μ-O)2](NO3)3 (2), and four MnII compounds, [{Mn(H2O)(phen)2}2(μ-4-COOC6H4COO)](NO3)2 (3), [Mn3(μ-4-COOC6H4COO)3(bpy)2]n (4), [{Mn(phen)2}2(μ-2-COOHC6H4COO)2](ClO4)2 (5) and [Mn(μ-2-COOC6H4COO)(H2O)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 MnIII (1) and MnIIIMnIV (2) compounds and −0.04, −4.5, −1.5 and −0.55 cm−1 for MnII compounds 4–6. Each MnII 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.

Phthalate and terephthalate ligands have been used for the synthesis of dinuclear MnIII and polynuclear MnII compounds. These ligands behave differently from other carboxylate ligands since analogous procedures reported before do not always lead to the expected compounds. One dinuclear MnIII compound and four polynuclear MnII compounds have been synthesised and structurally characterised (a mixed-valence compound without a carboxylate ligand has also been obtained). All the compounds show weak antiferromagnetic coupling and the MnII compounds can be differentiated by their EPR spectra at 4 K. Their catalase activity has also been studied.Figure optionsDownload as PowerPoint slide