Switching a 2D Co(II) layer to a 3D Co7-cluster-based metal-organic framework: syntheses, crystal structures, and magnetic properties.

Two 2D layered coordination networks with formulas of {[Co(TPA)Cl](H2O)2.5}n (1) and {[Co(TPA)(μ2-OH)](H2O)2}n (2) (HTPA = 4-(1,2,4-triazol-4-yl)phenylacetic acid) were solvothermally synthesized and fully characterized. Interesting 1D Co(2+)-Cl or Co(2+)-μ2-OH chain structures were observed. By carefully adjusting the reaction conditions, a new 3D metal-organic framework (MOF) with a formula of {[Co7(TPA)6(μ3-OH)4(μ2-OH)2(H2O)4](TPA)2(DMF)3(H2O)3}n (3) was obtained. MOF 3 is built from Co7 clusters and fully deprotonated TPA ligands, which display a cubic pcu topology. Factors that influence the structures of the three TPA-based complexes, as well as their magnetic properties, were investigated in detail. The heptanuclear-Co(II)-cluster-based MOF 3 shows interesting magnetization dynamics at low temperature.