Tuning Connectivity and Flexibility of Two Zinc-Triazolate-Carboxylate Type Porous Coordination Polymers

Solvothermal reactions of Zn­(II) salts and 4-(1<i>H</i>-pyrazol-4-yl)­pyridine (Hpypz) in the presence of monocarboxylate or dicarboxylate ligands produced two porous coordination polymers, namely, [Zn­(pypz)­(OAc)]­·guest (<b>1·g</b>, HOAc = acetic acid) and [Zn₂(pypz)₂­(oba)]­·guest (<b>2·g</b>, H₂oba = 4,4′-oxobisbenzoic acid). Single-crystal X-ray diffraction analyses showed that both <b>1</b> and <b>2</b> contain 2-fold interpenetrated three-dimensional <b>nbo-a</b> {Zn­(pypz)}⁺ networks consisting of 3-connected Zn­(II) ions and 3-connected pypz^– ligands. After the carboxylate ligands were considered, <b>1</b> retains the <b>nbo-a</b> network structure and contains one-dimensional channels with very narrow apertures. On the other hand, <b>2</b> becomes a new uninodal 6-connected topology (point symbol 3³.4².5⁶.6⁴) and contains discrete pores. Powder X-ray diffraction showed that, after solvent removal, <b>1</b> undergoes obvious framework shrinkage, while <b>2</b> retains the original unit cell. Activated <b>1</b> and <b>2</b> both exclude N₂ at 77 K, but readily adsorb CO₂ at 195 K with unconventional isotherm shapes, indicating the different types of framework flexibilities