One Atom Can Make All the Difference: Gas-Induced Phase Transformations in Bisimidazole-Linked Diamondoid Coordination Networks

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) (H(2)bdc = 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. Although X-dia-4-Co and X-dia-5-Co only differ from one another by one atom in their N-donor linkers (bimpy = pyridine, and bimbz = benzene), this results in different pore chemistry and switching mechanisms. Specifically, X-dia-4-Co exhibited a gradual phase transformation with a steady increase in the uptake when exposed to CO2, whereas X-dia-5-Co exhibited a sharp step (type F-IV isotherm) at P/P-0 approximate to 0.008 or P approximate to 3 bar (195 or 298 K, respectively). Single-crystal X-ray diffraction, in situ powder XRD, in situ IR, 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.

Automated summary

In this study, two coordination networks (CNs), X-dia-4-Co and X-dia-5-Co, undergo gas-induced transformations from closed to open structures with at least a 27% increase in cell volume. Although they only differ by one atom in their N-donor linkers, their pore chemistry and switching mechanisms show pronounced differences. Insight into these differences is provided through various experimental and computational techniques.