Energetics of formation and hydration of a porous metal organic nanotube

Sulata K. Sahu, Daniel K. Unruh, Tori Z. Forbes, Alexandra Navrotsky

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Hybrid materials, such as metal organic nanotubes (MON), are of interest because of their chemical tunability and permanent porosity. While an increasing number of compounds is being reported, very little is known about their thermodynamic stability. Herein, the energetics of a MON, (C4H12N2)0.5[(UO2)(Hida)(H2ida)]·2H2O (UMON, C10H21N3UO12) (ida = iminodiacetate), that possesses unique water exchange and uptake has been investigated by acid solution calorimetry, thermal analysis, and water adsorption calorimetry. The enthalpy of formation of UMON, C10H21N3UO12 (ΔHf,rxn), from the dense components (uranium oxide (UO3), piperazine (C4H10N2), and iminodiacetic acid (C4H7NO4) was ∼55.3 ± 0.9 kJ/mol, which was similar to values for other metal organic framework materials. The dehydration enthalpy to form an anhydrous UMON and gaseous H2O at 37 °C from thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC) experiments was 57.8 ± 1.9 kJ/mol of water. This value is somewhat higher than the vaporization enthalpy of water (44 kJ/mol) and suggests modest bonding interactions of H2O with the inner walls of the nanotubes. Water adsorption calorimetry of (C4H12N2)0.5[(UO2)(Hida)(H2ida)]·2H2O indicated that the water molecules are confined inside the UMON material in two thermally distinct positions. The ice-like arrangement of the confined water molecules inside the nanotube impacts the energetics of the material and adds to the stabilization of the structure.

Original languageEnglish (US)
Pages (from-to)5105-5112
Number of pages8
JournalChemistry of Materials
Issue number17
StatePublished - Sep 9 2014
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry


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