A rational
combination of an oxygen-rich pyridyl substituted tetrapodal ligand,
tetrakis(4-pyridyloxymethylene)methane (TPOM), and a polar sulfone-functionalized
conjugated bent dicarboxylate linker, dibenzothiophene-5,5′-dioxide-3,7-dicarboxylic
acid (H2(3,7-DBTDC)), with d10 metal centers,
Zn(II) and Cd(II), has led to the construction of two new three-dimensional
(3D) metal–organic frameworks,{[Zn2(TPOM)(3,7-DBTDC)2]·7H2O·DMA}
n
(1) and {[Cd2(TPOM)(3,7-DBTDC)2]·6H2O·3DMF}
n
(2). Single-crystal X-ray analysis indicates that 1 is a 3D framework with a dinuclear repeating unit having two different
Zn(II) centers (tetrahedral and square pyramidal) and 2 is a 3D framework comprised of a dinuclear repeating unit with one
crystallographically independent distorted pentagonal bipyramidal
Cd(II) coordinated to chelating/bridging carboxylates and nitrogen
atoms of the TPOM ligand. In both cases, the pores are aligned with
oxygen atoms of the TPOM ligand and decorated with polar sulfone moieties.
On the basis of the stability established by thermogravimetric analysis
and powder X-ray diffraction (PXRD) and the presence of large solvent
accessible voids (25.4% for 1 and 40.6% for 2), gas sorption studies of different gases (N2, CO2, and CH4) and water vapor have been explored for
both 1 and 2. The CO2 sorption
isotherm depicts type I isotherm with an uptake of 93.6 cm3 g–1 (for 1) and 100.6 cm3 g–1 (for 2) at 195 K. Additionally,
sorption of CO2 is highly selective over that of N2 and CH4 for both 1 and 2 due to the strong quadrupolar interactions between sulfone moieties
and CO2 molecules. Configurational bias Monte Carlo (CBMC)
molecular simulation has further justified the highly selective CO2 capture. On the other hand, the luminescence nature of 1 and 2 has been employed for highly selective
detection of acetylacetone in aqueous methanol with a limit of 59
ppb in 1 and 66 ppb in 2, which are among
the best reported values so far in the literature. The Stern–Volmer
plots, spectral overlap, density functional theory calculations, CBMC
simulation, and time-resolved lifetime measurements have been utilized
for an extensive mechanistic study. The exclusive selectivity for
acetylacetone in 1 and 2 have been confirmed
by competitive selectivity test. Both exhibited good recyclability
and stability after sensing experiments analyzed by fluorescence,
PXRD, and field emission scanning electron microscopy studies.