Pro-porous coordination polymers of the 1,4-bis((3,5-dimethyl-1H-pyrazol-4-yl)-methyl)benzene ligand with late transition metals

Solvothermal reactions of the flexible, pyrazole-based 1,4-bis((3,5- dimethyl-1H-pyrazol-4-yl)methyl)benzene ligand (H2BDMPX) with late transition metal ions allowed the isolation of the four coordination compounds Mx(BDMPX) (x = 1 for M = Zn, 1; Co, 2; Cd, 3; x = 2 for M = Cu, 4). The investigation of the thermal behavior assessed the high thermal robustness of these materials, which are stable in air at least up to 300 °C, with the Cd(II) derivative starting to decompose only around 500 °C. As retrieved by ab initio X-ray powder diffraction, the isomorphous compounds 1-3 possess a dense 3-D network featuring rhombic motifs hinged about rigid and parallel chains of tetrahedral MN4 chromophores. As demonstrated by thermodiffractometric measurements, temperature increase triggers framework flexibility. The latter is at work also when N2 adsorption is assayed at 77 K: 1 and 2 show permanent porosity, with BET and Langmuir specific surface areas of 515, 667 m2/g and 209, 384 m2/g, respectively. 1 and 2 thus represent an intriguing example of "porosity without pores", their pro-porous nature being explained in terms of the flexibility of the rhombic motifs, stimulated by the gas probe and facilitated by the nature of the ligand.