The ionothermal synthesis, structure, and magnetism-structure relationship of two biphenyl tetracarboxylic acid-based metal-organic frameworks

Two new metal-organic frameworks (1-2) were ionothermally obtained by the reaction of a biphenyl-tetracarboxylic sodium (Na4BPTC) ligand and M(OOCCH3)(2) (M = Co(1) and,Mn(2)). Crystal structure analysis reveals that 1 is a Co3Na6 unit-based three dimensional heterometallic MOF, while 2 exhibits a {Mn(COO)(n)} chain-based three-dimensional framework. Furthermore, the magnetic measurement shows that both of them have anti-ferromagnetic properties. A combination of Density Functional Theory (DFT) and Quantum Monte Carlo (QMC) simulation uncovers that in 2 the coupling parameters between two adjacent Mn(II) ions are J(1) = -2.0 cm(-1) and J(2) = -1.6 cm(-1), and the magnetism mainly originates from the propagation of Mn(II) ions by the super-exchange of carboxylates. Interestingly, the superexchange modes of J(1) and J(2) are different. Two spin nets of -/+/- dominate in the coupling for J(1), while for J(2) there are two spin nets of -/+/- and one spin net of +/-/+.