Control of the Coordination
Status of the Open Metal
Sites in Metal–Organic Frameworks for High Performance Separation
of Polar Compounds
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Abstract
Metal–organic frameworks (MOFs) with open metal
sites have
great potential for enhancing adsorption separation of the molecules
with different polarities. However, the elution and separation of
polar compounds on such MOFs packed columns using nonpolar solvents
is difficult due to too strong interaction between polar compounds
and the open metal sites. Here, we report the control of the coordination
status of the open metal sites in MOFs by adjusting the content of
methanol (MeOH) in the mobile phase for fast and high-resolution separation
of polar compounds. To this end, high-performance liquid chromatographic
separation of nitroaniline, aminophenol and naphthol isomers, sulfadimidine,
and sulfanilamide on the column packed with MIL-101(Cr) possessing
open metal sites was performed. The interaction between the open metal
sites of MIL-101(Cr) and the polar analytes was adjusted by adding
an appropriate amount of MeOH to the mobile phase to achieve the effective
separation of the polar analytes due to the competition of MeOH with
the analytes for the open metal sites. Fourier transform infrared
spectra and X-ray photoelectron spectra confirmed the interaction
between MeOH and the open metal sites of MIL-101(Cr). Thermodynamic
parameters were measured to evaluate the effect of the content of
MeOH in the mobile phase on the separation of polar analytes on MIL-101(Cr)
packed column. This approach provides reproducible and high performance
separation of polar compounds on the open metal sites-containing MOFs