In this work, we present the first metal–organic
framework
(MOF) platform with a self-penetrated double diamondoid (ddi) topology that exhibits switching between closed (nonporous) and
open (porous) phases induced by exposure to gases. A crystal engineering
strategy, linker ligand substitution, was used to control gas sorption
properties for CO2and C3 gases. Specifically, bimbz (1,4-bis(imidazol-1-yl)benzene)
in the coordination networkX-ddi-1-Ni([Ni2(bimbz)2(bdc)2(H2O)]n, H2bdc = 1,4-benzenedicarboxylic acid)
was replaced by bimpz (3,6-bis(imidazol-1-yl)pyridazine) inX-ddi-2-Ni([Ni2(bimpz)2(bdc)2(H2O)]n). In addition, the
1:1 mixed crystalX-ddi-1,2-Ni([Ni2(bimbz)(bimpz)(bdc)2(H2O)]n) was prepared
and studied. All three variants form isostructural closed (β) phases upon activation which each exhibited different reversible
properties upon exposure to CO2at 195 K and C3 gases at
273 K. For CO2,X-ddi-1-Nirevealed incomplete
gate-opening,X-ddi-2-Niexhibited a stepped isotherm
with saturation uptake of 3.92 mol·mol–1, andX-ddi-1,2-Niachieved up to 62% more gas uptake and a distinct
isotherm shape vs the parent materials. Single-crystal X-ray diffraction
(SCXRD) andin situpowder X-ray diffraction (PXRD)
experiments provided insight into the mechanisms of phase transformation
and revealed that theβphases are nonporous with
unit cell volumes 39.9, 40.8, and 41.0% lower than the corresponding
as-synthesizedαphases,X-ddi-1-Ni-α,X-ddi-2-Ni-α, andX-ddi-1,2-Ni-α, respectively. The results presented herein represent the first
report of reversible switching between closed and open phases indditopology coordination networks and further highlight how
ligand substitution can profoundly impact the gas sorption properties
of switching sorbents.