Functionalities of one-dimensional dynamic ultramicropores in nickel(II) coordination polymers

Ni-II coordination polymers with a 4,4 '-azobis(pyridine) (azpy) ligand, {[Ni-2(NCX)(4)(azpy)(4)]center dot G}(n) (X = S, G (guest molecule) = MeOH (1 center dot MeOH); X = S, G = EtOH (1 center dot EtOH); X = S, G = H2O (1 center dot H2O); X = S, G = no guest (1); X = Se, G = MeOH (2 center dot MeOH); X = Se, G = H2O (2 center dot H2O); X = Se, G = no guest ( 2)), have been synthesized and structurally characterized with their porosity. These compounds have one-dimensional periodic ultramicropores that contain the small guest molecules, H2O, MeOH, or EtOH, whose hydroxy groups interact with the S or Se atoms of isothiocyanate or isoselenocyanate, respectively, via-S(Se)center dot center dot center dot HO-hydrogen bonds. Although the molecular dimensions of the MeOH guest are considerably larger than the window size of the ultramicropore, 1, MeOH and 2, MeOH easily release their guest molecules without decomposition of the framework to form 1 and 2 without any guest molecules. This shows that 1 and 2 have dynamic ultramicropores constructed from the interpenetrating framework. The guest desorption experiments using 1 center dot MeOH and 1 center dot 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-2 and CH4 adsorption isotherms was observed and is associated with the strength of the host-guest interaction.