Functionalities of One-Dimensional Dynamic Ultramicropores in Nickel(II) Coordination Polymers

Ni<sup>II</sup> coordination polymers with a 4,4‘-azobis(pyridine) (azpy) ligand, {[Ni<sub>2</sub>(NCX)<sub>4</sub>(azpy)<sub>4</sub>]·G}<i><sub>n</sub></i> (X = S, G (guest molecule) = MeOH (<b>1</b>·MeOH); X = S, G = EtOH (<b>1</b>·EtOH); X = S, G = H<sub>2</sub>O (<b>1</b>·H<sub>2</sub>O); X = S, G = no guest (<b>1</b>); X = Se, G = MeOH (<b>2</b>·MeOH); X = Se, G = H<sub>2</sub>O (<b>2</b>·H<sub>2</sub>O); X = Se, G = no guest (<b>2</b>)), have been synthesized and structurally characterized with their porosity. These compounds have one-dimensional periodic ultramicropores that contain the small guest molecules, H<sub>2</sub>O, MeOH, or EtOH, whose hydroxy groups interact with the S or Se atoms of isothiocyanate or isoselenocyanate, respectively, via −S(Se)···HO− hydrogen bonds. Although the molecular dimensions of the MeOH guest are considerably larger than the window size of the ultramicropore, <b>1</b>·MeOH and <b>2</b>·MeOH easily release their guest molecules without decomposition of the framework to form <b>1</b> and <b>2</b> without any guest molecules. This shows that <b>1</b> and <b>2</b> have dynamic ultramicropores constructed from the interpenetrating framework. The guest desorption experiments using <b>1</b>·MeOH and <b>1</b>·EtOH reveal that the difference in the desorption behavior is due to van der Waals interactions that depend on the molecular shape of the guest molecule in the ultramicropores and/or an entrance blocking effect that depends on the minimum dimensions of the guest molecule for the pore windows. A marked difference in the N<sub>2</sub> and CH<sub>4</sub> adsorption isotherms was observed and is associated with the strength of the host−guest interaction.