Metal Substitution into Metal Organic Nanotubes: Impacts on Solvent Uptake and Stability

Transition metal dopants can be incorporated in metal organic frameworks to change the physical properties of the material. Metal organic nanotubes are a less well studied form of hybrid material, and in this study, transition metals were substituted into U(VI) metal organic nanotubes (UMON) to investigate changes with water uptake, solvent selectivity, and hydrostability. Single-crystal X-ray analysis, UV/vis spectroscopy, and electron microprobe analysis confirmed the substitution of (VO)(2+), Co(II), Fe(II), and Cu(II), with the highest amount of incorporation by Cu(II). Water uptake and release by the substituted materials were similar to that of the pure UMON sample, with the exception in the Cu(II)-UMON samples, where less water present in the nanotubular cavities and additional heating were necessary for dehydration. A detailed investigation of the Cu(II)-UMON material indicated that the overall selectivity of the material was maintained and the hydrostability was drastically enhanced with incorporation. In the presence of ammonia, the pure and doped UMON material degraded to secondary phases.