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

• Published in: Crystal growth & design Vol. 13; no. 7; pp. 2973 - 2981
• Main Authors: Kinnibrugh, Tiffany L, Ayi, Ayi A, Bakhmutov, Vladimir I, Zoń, Jerzy, Clearfield, Abraham
• Format: Journal Article
• Language: English
• Published: Washington,DC American Chemical Society 03.07.2013
• Subjects: Condensed matter: structure, mechanical and thermal properties; Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder; Cross-disciplinary physics: materials science; rheology; Crystalline state (including molecular motions in solids); Crystallographic aspects of phase transformations; pressure effects; Exact sciences and technology; Materials science; Organic compounds; Other materials; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Specific materials; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Metal organic framework; Amines; Electrical conductivity; Phase transformations; Organometallic compounds; Phosphonates; Lithium; XRD; Physical properties; Ion exchange materials; Monocrystals; Hydrothermal synthesis; Crystal-phase transformations; Chemical properties; Nuclear magnetic resonance; Crystal structure
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg400399v

A one-step hydrothermal synthesis with small amines and 1,3,5-benzenetriphosphonic acid was used to prepare single crystals of isostructural anionic metal–organic frameworks (MOF): Zn2.5(H)0.4– 0.5(C6H3O9P3)(H2O)1.9–2(NH4)0.5–0.6 and Zn2.5(H)0.75(C6H3O9P3)(H2O)2(CH3NH3)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.