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 Co²⁺-Cl or Co²⁺-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.