Pro-porous Coordination Polymers of the 1,4-Bis((3,5-dimethyl-1<i>H</i>-pyrazol-4-yl)-methyl)benzene Ligand with Late Transition Metals

Solvothermal reactions of the flexible, pyrazole-based 1,4-bis((3,5-dimethyl-1<i>H</i>-pyrazol-4-yl)methyl)benzene ligand (H₂BDMPX) with late transition metal ions allowed the isolation of the four coordination compounds M_<i>x</i>(BDMPX) (<i>x</i> = 1 for M = Zn, <b>1</b>; Co, <b>2</b>; Cd, <b>3</b>; <i>x</i> = 2 for M = Cu, <b>4</b>). 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 <b>1</b>–<b>3</b> 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: <b>1</b> and <b>2</b> show permanent porosity, with BET and Langmuir specific surface areas of 515, 667 m²/g and 209, 384 m²/g, respectively. <b>1</b> and <b>2</b> 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