Coordination networks
(CNs) that undergo gas-induced transformation
from closed (nonporous) to open (porous) structures are of potential
utility in gas storage applications, but their development is hindered
by limited control over their switching mechanisms and pressures.
In this work, we report two CNs, [Co(bimpy)(bdc)]n(X-dia-4-Co) and [Co(bimbz)(bdc)]n(X-dia-5-Co) (H2bdc = 1,4-benzendicarboxylic
acid; bimpy = 2,5-bis(1H-imidazole-1-yl)pyridine; bimbz = 1,4-bis(1H-imidazole-1-yl)benzene),
that both undergo transformation from closed to isostructural open
phases involving at least a 27% increase in cell volume. AlthoughX-dia-4-CoandX-dia-5-Coonly differ from one
another by one atom in theirN-donor linkers (bimpy
= pyridine, and bimbz = benzene), this results in different pore chemistry
and switching mechanisms. Specifically,X-dia-4-Coexhibited
a gradual phase transformation with a steady increase in the uptake
when exposed to CO2, whereasX-dia-5-Coexhibited
a sharp step (type F-IV isotherm) atP/P00.008 orP3 bar (195 or 298 K, respectively). Single-crystal
X-ray diffraction,in situpowder XRD,in
situIR, and modeling (density functional theory calculations,
and canonical Monte Carlo simulations) studies provide insights into
the nature of the switching mechanisms and enable attribution of pronounced
differences in sorption properties to the changed pore chemistry.