Hydrothermal syntheses, structures, and magnetic properties of two new Mn(II) complexes with biphenyl-2,3,3′,5′-tetracarboxylic acid

Two metal–organic frameworks [Mn4(bptc)2(bpy)2]n (1) (H4bptc = biphenyl-2,3,3′,5′-tetra-carboxylic acid, bpy = 2, 2′-dipyridine) with Mn4 clusters and {[Mn2(bptc)2(H2O)8]⋅4H2O}(2) were obtained through hydrothermal reaction. X-ray diffraction analysis shows that both complexes 1 and 2 crystallize in the Triclinic system, space group of P-1. The Mn(II) ions have two kinds of coordination mode in complex 1, one is five- coordinated and the other is six-coordinated. Mn(2) ion is bridged to neighboring Mn(2)A(A:1 − x, 1 − y, 2 − z) by two μ2-Ocarboxyl atoms to afford a {Mn}4 cluster together with another two symmetrical Mn(1) and Mn(1)a. The {Mn}4 clusters are further connected through the bptc4− ligands each other, giving rise to a 2D network. There is a Mn2O2 parallelogram-core in every {Mn}4 cluster, and to the best of our knowledge this is the first time observed. Complex 2 consists of the dinuclear manganese (II) unit, which is further linked by hydrogen bonds to form a 3D framework structure. Magnetic measurements show there is a weak anti-ferromagnetic interaction in complex 1. Moreover, the IR, element analysis, and thermal stability of the two complexes have been investigated systemically.