Enlarging an Isoreticular Family: 3,3′,5,5′-Tetramethyl-4,4′-bipyrazolato-Based Porous Coordination Polymers

The solvothermal reaction between the rigid spacer 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (H2Me4BPZ) and a number of transition metal salts promoted the formation of the coordination polymers [M­(Me4BPZ)] (M = Zn, 1; Co, 2; Cd, 3; Cu, 4). Ab initio X-ray powder diffraction analyses revealed the main structural aspects of the four materials. 1 and 2 are representative examples of the so-called isoreticular strategy: isostructural to [M­(BPZ)] and [M­(BDP)] (H2BPZ = 4,4′-bipyrazole; H2BDP = 1,4-bis­(1H-pyrazol-4-yl)­benzene), they feature three-dimensional (3-D) porous networks containing square-shaped channels. In 3, tetrahedral Cd­(II) ions are arranged within homochiral helices reciprocally linked by radial Me4BPZ spacers, overall creating a 3-D nonporous network. Finally, the 3-D porous framework of 4 comprises square Cu4 nodes linked to eight neighboring ones by the bridging spacers. Thermogravimetric analyses, coupled to variable-temperature X-ray powder diffraction, demonstrated the remarkable thermal robustness of all the materials, decomposing above 300 °C, and their stability for consecutive heating–cooling cycles. N2 and CO2 adsorption measurements at 77 and 273 K, respectively, were employed to probe the permanent porosity of the materials and to give a coherent picture of their textural properties including specific surface areas, micro- and mesopore volumes, as well as size distributions.