Solvent-Controlled Syntheses, Structure, and Magnetic Properties of Trinuclear Mn(II)-Based Metal-Organic Frameworks

Solvothermal reactions of manganese(II) salts with hexa[4-(carboxyphenyl)oxamethyl]-3-oxapentane acid (H6L) afforded a family of porous metal-organic frameworks, namely, Mn-3(L)(DMA)(4)center dot 2DMA (1, C2/c), Mn-3(L)(H2O)(2)(DMF)(2)center dot 8DMF (2, Cc), and Mn-3(L)(H2O)(2)(DMF)center dot 4DMF (3, P2(1)/c). All compounds have been characterized by elemental analysis and thermogravimetric analysis and structurally confirmed by single-crystal X-ray diffractions. Their structures consist of three types of trinuclear Mn-II subunits, which are further bridged by the carboxylic ligand, resulting in two types of topological nets (pts and sra). All of the Mn-3(II) subunits are terminally coordinated by solvent molecules. The structure of the Mn-3(II) core in 1 is symmetric with an inversion center, whereas those in 2 and 3 display a symmetry-breaking phenomenon. Their magnetic behaviors exhibit interesting variations, in which the local net magnetization at low temperature increases gradually from 1 to 3. Such magnetic evolution behavior in trinuclear subunits has never been observed previously.