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.