Probing Structural Changes in a Phosphonate-based Metal–Organic Framework Exhibiting Reversible Dehydration

Abstract

A one-step hydrothermal synthesis with small amines and 1,3,5-benzenetriphosphonic acid was used to prepare single crystals of i s o s t r u c t u r a l a n i o n i c m e t a l − o r g a n i c f r a m e w o r k s ( M O F ) : Z n 2 . 5 ( H ) 0 . 4 − 0 . 5 ( C 6 H 3 O 9 P 3 ) ( H 2 O ) 1 . 9 − 2 ( N H 4 ) 0 . 5 − 0 . 6 a n d Zn 2.5 (H) 0.75 (C 6 H 3 O 9 P 3 )(H 2 O) 2 (CH 3 NH 3 ) 0.25 . The ammonium ions are exchangeable with lithium ions. The MOF exhibits reversible dehydration, and the process was studied by two complementary methods: solid state NMR and in situ X-ray diffraction. These experiments revealed three different phases. The crystal structures of all phases have been determined, showing loss in volume of the structure due to a phase change. The ammonium ions remain in the structure and are forced to occupy the larger pores due to a reduction in free volume. The change in positions of the guest molecules in the framework has an effect on the potential conductivity properties of the materials. Changes in framework and guest molecules due to negative expansion have an effect on other physical and chemical properties and need to be explored.

Complete multinuclear solid‐state NMR of metal‐organic frameworks: The case of α‐Mg‐formate

“…1 H SSNMR can be employed to obtain detailed structural data that is truly complementary to XRD, yet this characterization route is not straightforward due to strong 1 H‐ 1 H homonuclear dipolar coupling that can severely broaden spectra, which arises from the spatial density of hydrogen in MOFs along with the very high 1 H gyromagnetic ratio (γ). Using high‐resolution 1 H SSNMR techniques it is possible to obtain well‐resolved 1 H resonances in MOFs, including those from chemically different species such as phenyl, methyl, amine, and hydroxyl groups. A more challenging situation arises when there are chemically identical but crystallographically non‐equivalent hydrogen atoms; in this situation, the similar 1 H chemical shifts (CSs) and strong 1 H‐ 1 H dipolar coupling result in very complicated lineshapes and overlapping resonances within a narrow CS range that cannot be resolved.…”

Chemistry of Metal-organic Frameworks Monitored by Advanced X-ray Diffraction and Scattering Techniques

“…128 Negative structure expansion of Zn-1,3,5-benzenetriphosphonate caused by the dehydration is elucidated by in-situ XRPD. 129 The [Zn 2 (fu-L) 2 …”

Modification and Potential Applications of Organic–Inorganic Non-Siliceous Hybrid Materials

“…In addition to the excellent proton conductivity, the hybrid was fully protonated by adding HCl and then subjected to several acid-base ion-exchange reactions with alkaline metal ions, such as Li + , Na + , and K + . Anionic MOF of Zn 2.5 (H) 0.4-0.5 (C 6 H 3 O 9 P 3 )(H 2 O) 1.9-2 (NH 4 ) 0.5-0.6 was synthesized with the use of urea and 1,3,5-benzenetriphosphonic acid [66], in which ammonium ions are exchangeable with Li + . Due to a certain degree of flexibility of the hybrid framework, a reversible insertion/desertion of Li + through the pores and elastic network can be envisioned, showing potential for secondary batteries.…”