A 36-Fold Multiple Unit Cell and Switchable Anisotropic Dielectric Responses in an Ammonium Magnesium Formate Framework

• Published in: Angewandte Chemie International Edition Vol. 54; no. 8; pp. 2534 - 2537
• Main Authors: Shang, Ran, Wang, Zhe-Ming, Gao, Song
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 16.02.2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Ammonium; ammonium metal formate; Anisotropy; Cations; Dielectric constant; dielectricity; Displays; Formates; High temperature; Holes; Low temperature; Magnesium; metal-organic frameworks; multiple unit cell; phase transition; Three dimensional; Unit cell; multiple unit cell; dielectricity; phase transition; ammonium metal formate; metal-organic frameworks
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.201411005

An ammonium Mg formate framework, prepared by using di‐protonated 1,3‐propanediamine (pnH22+), has a rare three‐dimensional binodal (412⋅63)(49⋅66)3 Mg‐formate framework with elongated cavities accommodating pnH22+⋅⋅⋅H2O⋅⋅⋅pnH22+ assemblies. It displays a para‐electric to antiferroelectric phase transition at 275 K, with a 36‐fold multiple unit cell from the high‐temperature cell of 1703 Å3 to the low‐temperature one of 60 980 Å3. The change results from the disorder–order transition of the pnH22+ cations and H2O molecules. The motions of these components freeze in a stepwise fashion on going from the high‐temperature disorder state to the low‐temperature ordered state, triggering the switch from high to low dielectric constants, and the spatial limitation of such motions contributes the strong dielectric anisotropy. Multiply the unit cell: An ammonium Mg formate framework has a rare three‐dimensional binodal framework with long cavities accommodating 1,3‐propanediammonium and water. The framework displays a phase transition at 275 K to give a 36‐fold multiple unit cell and anisotropic switchable dielectric responses.