Structural Features in Metal–Organic Nanotube Crystals That Influence Stability and Solvent Uptake

Porous hybrid materials such as metal–organic
nanotubes are of interest due to synthetic tunability, possibility
for 1-D flow, and confinement of solvent molecules. In the current
study, the stability and solvent selectivity of two hybrid materials
with nanotubular arrays, (pip)0.5[(UO2)­(HIDA)­(H2IDA)]·2H2O (UIDA; IDA = iminodiacetate)
and [(UO2)­(PDC)­(H2O)] (UPDC; PDC
= pyridine dicarboxylate) were analyzed using X-ray diffraction, gas
chromatography/mass spectrometry, thermogravimetric analysis, and
infrared spectroscopy. The fine details of the structural characterization,
such as the presence of solvent molecules, were found to be important
to the overall properties of the materials as evidenced by the increased
stability of the UIDA compound when formed from a solvent
mixture containing acetone. Careful analysis of the UPDC compound indicated that the ligated solvent molecule can be exchanged,
which may impact the hydration state of the material. Overall, the UIDA compound displays complete selectivity to water, but
the UPDC compound adsorbs THF, methanol, ethanol, and
cyclohexane.