Syntheses, crystal structures and magnetic properties of a novel family of penta-manganese complexes derived from an assembly system containing polydentate hydroxy-rich Schiff-base ligands

Abstract

The syntheses, crystal structures, and magnetochemical characterization are reported of a novel family of four pentanuclear manganese complexes, namely, [Mn^III₅(μ₃-O)₂(L₁)₄(O₂CMe)₃(CH₃OH)]·1.5CH₃OH·2.5H₂O (1), [Mn^III₅(μ₃-O)₂(L₁)₄(O₂CPh)₃(CH₃OH)]·2CH₃OH·2.25CH₃CN·1.5H₂O (2), [Mn^IIMn^III₄(HL₂)₂(L₂)₂(O₂C Me)₄)]·CH₃OH·H₂O (3) and [Mn^IIMn^III₄(HL₂)₂(L₂)₂(O₂CPh)₄)]·1.5H₂O (4), where H₂L₁ is 3,5-dibromosalicylidene-2-ethanolamine and H₃L₂ is 3-(2-hydroxy-3,5-dibromobenzylideneamino)propane-1,2-diol. All the complexes can be obtained from a reaction system containing the trinuclear species [Mn₃O(O₂CR)₆(Py)₃]^0/+ (R = Me or Ph) and H₂L₁ or H₃L₂ with similar procedures. Both cores in complexes 1 and 2 feature two μ₃-O²⁻ atoms, four L₁²⁻ ligands together with three RCO₂⁻ groups (R = Me or Ph) bridging five Mn^III atoms to form an incomplete cubane extended at one face by an incomplete adamantane unit, which is an unprecedented structural type in Mn chemistry. Complexes 3 and 4 both have a rare [Mn^IIMn^III₄(μ₂-O_alkoxide)₆]⁸⁺ core, which can be regarded as two {Mn^IIMn^III₂(μ₂-O_alkoxide)₃} scalene triangles, sharing the Mn^II vertex. The dc magnetic susceptibility studies in the 2–300 K range for complexes 1–4 reveal the presence of overall antiferromagnetic intracluster interactions. A simple 3-J model was found to be adequate to describe the variable-temperature dc susceptibility data of complexes 1–4. The results have allowed us to compare the obtained magnetic exchange with magneto–structural correlations found previously for manganese-oxo clusters.