Novel Coordination Frameworks Incorporating the 4,4′-Bipyrazolyl Ditopic Ligand

The reaction of the rigid spacer 4,4′-bipyrazole
(H2BPZ) with late transition metals, either following conventional
routes or under solvothermal conditions, afforded the coordination
polymers [M­(BPZ)]·Solv (M = Zn, 1; Co, 2; Cd, 3; Hg, 4; Cu, 5; Ni, 6; Pd, 7; Solv = DMF, 3; MeCN, 5 and 6; H2O, 7), [Cu­(H2BPZ)2(NO3)2] (8), and [Cd­(H2BPZ)­(CH3COO)2] (9). State-of-the-art laboratory powder diffraction methods
allowed to disclose the isomorphous character of 1 and 2, as well as of 5 and 6, which
feature 3D porous networks containing 1D channels of square and rhombic
shape, respectively. 3, crystallizing in the relatively
rare P6122 space group, consists of homochiral
helices of octahedral CdII ions, packing in bundles mutually
linked by “radial”, nonplanar BPZ ligands. Finally,
the dense species 8 and 9 contain parallel
2D layers of square and rectangular meshes, respectively. Thermogravimetric
analyses witnessed the relevant thermal robustness of all the [M­(BPZ)]
materials [except the mercury­(II) derivative], which are stable in
air at least up to 300 °C, with the zinc­(II) derivative decomposing
only around 450 °C. Variable-temperature powder diffraction experiments
highlighted the permanent porosity of 1–3, 5, and 6, retained along consecutive
temperature cycles in all cases but 3. When probed with
N2 at 77 K, 1–3 and 5–7 showed Brunauer–Emmett–Teller
and Langmuir specific surface areas in the ranges 314(2)–993(11)
and 509(16)–1105(1) m2/g, respectively.