Influence of Mn/Ca ratio in Mn-Ca Coordination Clusters: Synthesis, Structure, and Magnetic Characterisation

Similar reactions of MnCl2·4H2O and CaCl2 with 2,6-bis(hydroxymethyl)-4-methylphenol gave heterometallic coordination clusters with very different nuclearities, depending on the Mn:Ca ratio used. With a 1:1 ratio, the hexanuclear cluster [MnIII3CaII3(μ3-Cl(HLMe)6(H2O)6]Cl2∙6.74H2O (2) with a “triangle-in-triangle” topology was obtained. However, a Mn:Ca ratio of 2:1 resulted in [MnIII12MnIICaII6(μ4-O)8(μ3-Cl)3.7(μ3-η1-N3)4.3(HLMe)12(MeCN)6]Cl2∙15MeOH (3), which corresponds structurally to the replacement by Ca2+ of six of the seven MnII centers in our previously-published cluster [MnIII12MnII7(μ4-O)8 (μ3-η1-N3)8(HLMe)12(MeCN)6]Cl2. Magnetic studies showed that the three MnIII centers in 2 are moderately antiferromagnetically coupled, while the results for 3 allowed an experimental estimate of the MnIII-MnIII coupling in the original [Mn19] cluster.