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Aliphatic Dicarboxylate Ligands Assemble Weakly Coupled Molecular Pairs of [MnIII]2 Units



Seven new tetranuclear MnIII compounds have been obtained by assembling two dinuclear units, [{Mn(L)(NN)}2(μ-O)]4+, with aliphatic dicarboxylate ligands COO(CH2)nCOO2–: succinato (n = 2, C42–), glutarato (n = 3, C52–) and adipato (n = 4, C62–), and NN = 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen). The general formula for these compounds is [{Mn(L)(NN)}4(μ-Cm)2(μ-O)2]X4 [X = ClO4, NN = bpy and Cm = C4 (1), C5 (2) and C6 (3); X = ClO4, NN = phen and Cm = C4 (4), C5 (5) and C6 (6); X = NO3, NN = bpy and Cm = C5 (7)]. Compounds 1, 2 and 4 were characterized by X-ray diffraction, which confirmed the assembly of two dinuclear entities. The magnetic properties of the seven compounds were studied and the results indicate that the main interaction takes place within the dinuclear units. Compound 4 shows a dominant ferromagnetic coupling with J = 4.0 cm–1, while the rest of compounds display antiferromagnetic couplings with J values of –2.8 (1), –1.9 (2), –3.3 (3), –0.3 (5), –0.4 (6) and –9.3 cm–1 (7), which are all in agreement with magneto-structural correlations. In the case of compound 4, a weak but significant antiferromagnetic coupling of the S = 4 [MnIII]2 subunits with an interaction constant of –0.9 cm–1 was observed.