Optimized Separation of Acetylene from Carbon Dioxide and Ethylene in a Microporous Material

Selective
separation of acetylene (C2H2)
from carbon dioxide (CO2) or ethylene (C2H4) needs specific porous materials whose pores can realize
sieving effects while pore surfaces can differentiate their recognitions
for these molecules of similar molecular sizes and physical properties.
We report a microporous material [Zn­(dps)2(SiF6)] (UTSA-300, dps = 4,4′-dipyridylsulfide) with
two-dimensional channels of about 3.3 Å, well-matched for the
molecular sizes of C2H2. After activation, the
network was transformed to its closed-pore phase, UTSA-300a, with dispersed 0D cavities, accompanied by conformation change
of the pyridyl ligand and rotation of SiF62– pillars. Strong C–H···F and π–π
stacking interactions are found in closed-pore UTSA-300a, resulting in shrinkage of the structure. Interestingly, UTSA-300a takes up quite a large amounts of acetylene (76.4 cm3 g–1), while showing complete C2H4 and CO2 exclusion from C2H2 under ambient conditions. Neutron powder diffraction and molecular
modeling studies clearly reveal that a C2H2 molecule
primarily binds to two hexafluorosilicate F atoms in a head-on orientation,
breaking the original intranetwork hydrogen bond and subsequently
expanding to open-pore structure. Crystal structures, gas sorption
isotherms, molecular modeling, experimental breakthrough experiment,
and selectivity calculation comprehensively demonstrated this unique
metal–organic framework material for highly selective C2H2/CO2 and C2H2/C2H4 separation.