Tuning the Molecular and Cationic Affinity in a Series of Multifunctional Metal–Organic Frameworks Based on Dodecanuclear Zn(II) Carboxylate Wheels

A series of new zinc­(II)–thiophene-2,5-dicarboxylate
(tdc)
MOFs based on novel dodecanuclear wheel-shaped building blocks has
been synthesized in almost quantative yields. Single-crystal X-ray
diffraction analyses reveal 3D porous frameworks with a complex composition
[Zn12(tdc)6(glycolate)6(dabco)3] where glycolate is a deprotonated polyatomic alcohol (ethylene
glycol, EgO2, 1; 1,2-propanediol, PrO2, 2; 1,2-butanediol, BuO2, 3; 1,2-pentanediol, PeO2, 4; glycerol, GlO2, 5) and dabco is 1,4-diazo[2.2.2.]­bicyclooctane.
All compounds 1–5 are isostructural
except for pendant groups of the diols decorating the surface of channels.
The adsorption of small gases (N2, CO2, CH4, C2H2, C2H4,
C2H6) and larger hydrocarbons (benzene, cyclohexane)
both in liquid and vapor phases was thoroughly investigated for all
compounds. The zero-coverage adsorption enthalpies, Henry constants,
and selectivity factors by various models are calculated and discussed.
The versatile adsorption functionality of the title series results
from the variable nature of the diol and could be tailored for a specific
adsorbate system. For example, 1 shows excellent selectivity
of benzene over cyclohexane (20:1 for vapors, 92:1 for liquid phase),
while 4 demonstrates unprecedented adsorption preference
of cyclohexane over benzene (selectivity up to 5:1). The compound 5 demonstrates great adsorption selectivity for CO2/N2 (up to 75.1), CO2/CH4 (up to
7.7), C2H2/CH4 (up to 14.2), and
C2H4/CH4 (up to 9.4). Also, due to
polar nature of the pores, 5 features size-selective
sorption of alkaline metal cations in order Li+ > Na+ > K+ > Cs+ as well as a notable
luminescent
response for cesium­(I) ions and urea.