Bis(pyrazolato)-based metal-organic frameworks fabricated with 4,4'-bis((3,5-dimethyl-1 H -pyrazol-4-yl)methyl)biphenyl and late transition metals

The reaction between the flexible, bis(pyrazolato)-based ligand 4,4'-bis((3,5-dimethyl-1H-pyrazol-4-yl)methyl)biphenyl (H2DMPMB) and late transition metal ions allowed the isolation of the two series of thermally stable metal-organic frameworks [M(DMPMB)] (M = Co, Zn, Cd) and [M 2(DMPMB)] (M = Cu, Ag). X-ray powder diffraction (XRPD) structure determinations demonstrated that the anti conformation adopted by the ligand, juxtaposed to its exo-tetradentate coordination mode, induces the formation of a 3-D architecture with nonpervious 1-D channels in the three isomorphous species [M(DMPMB)] and of corrugated 2-D layers in [Cu2(DMPMB)]. Coupling thermogravimetric analyses and variable temperature XRPD highlighted that the five materials are thermally stable at least up to 300 °C, both under nitrogen and in air, the Cd(II) derivative decomposing only at the remarkably high temperature of 500 °C. No thermal event could be detected; all the materials preserve their structural motifs up to decomposition. The adsorption properties of the five compounds were assayed toward N2 at 77 K: while no adsorption was observed for [Cd(DMPMB)], the other species possess estimated BET and Langmuir specific surface areas in the ranges 64(1)-526(3) m2/g and 142(4)-713(27) m2/g, respectively, thus being an example of the interesting phenomenon known as "porosity without pores". Finally, the luminescence properties of the Zn(II), Cd(II), and Cu(I) derivatives were investigated.