A Water-Stable Anionic Metal–Organic Framework Constructed from Columnar Zinc-Adeninate Units for Highly Selective Light Hydrocarbon Separation and Efficient Separation of Organic Dyes

A metal–organic
framework (MOF), {(Me2NH2)2[Zn6(μ4-O)­(ad)4(BPDC)4]}n (JXNU-4; ad– = adeninate), with an anionic three-dimensional (3D) framework constructed
from one-dimensional (1D) columnar [Zn6(ad)4(μ4-O)]n secondary building
units (SBUs) and 4,4′-biphenyldicarboxylate (BPDC2–) ligand, was prepared. The anionic 3D framework has 1D square channels
with an aperture of about 9.8 Å and exhibits a carboxylate-O-decorated
pore environment. The microporous nature of JXNU-4 was
established by the N2 adsorption data, which gives Langmuir
and Brumauer–Emmett–Teller surface areas of 1800 and
1250 m2 g–1, respectively. Noticeably, JXNU-4 shows potential as a separation agent for the selective
removal of propane and ethane from natural gas with high selectivities
of 144 for C3H8/CH4 (5:95) and 14.6
for C2H6/CH4 (5:95), respectively.
Most importantly, JXNU-4 shows an aqueous-phase adsorption
of a positively charged ion of methylene blue selectively over a negatively
charged ion of resorufin, which is pertinent to the anionic nature
of the framework, and provides a size-exclusive sieving of methylene
blue over other positively charged ions of Janus Green B and ethyl
violet, which is relevant to its pore structure, enabling the efficient
aqueous-phase separation of organic dyes.