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, Mn3(L)­(DMA)4·2DMA (1, C2/c), Mn3(L)­(H2O)2(DMF)2·8DMF (2, Cc), and Mn3(L)­(H2O)2(DMF)·4DMF (3, P21/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 MnII subunits, which are further
bridged by the carboxylic ligand, resulting in two types of topological
nets (pts and sra). All of the MnII3 subunits
are terminally coordinated by solvent molecules. The structure of
the MnII3 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.