A Copper–Formate Framework Showing a Simple to Helical Antiferroelectric Transition with Prominent Dielectric Anomalies and Anisotropic Thermal Expansion, and Antiferromagnetism. Issue 48 (9th October 2014)

• Record Type: Journal Article
• Authors: Shang, Ran; Chen, Sa; Wang, Zhe‐Ming; Gao, Song
• Is Part Of: Chemistry. Volume 20:Issue 48(2014)
• Page Start: 15872
• Page End: 15883
• Publication Date: 2014-10-09
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201403466
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>We present here the compound [NH<sub>4</sub>][Cu(HCOO)<sub>3</sub>], a new member of the [NH<sub>4</sub>][M(HCOO)<sub>3</sub>] family. The Jahn–Teller Cu<sup>2+</sup> ion leads to a distorted 4<sup>9</sup>⋅6<sup>6</sup> chiral Cu–formate framework. In the low‐temperature (LT) orthorhombic phase, the Cu<sup>2+</sup> is in an elongated octahedron, and the <inline-formula><alternatives><tex-math notation="tex"><![CDATA[${{\rm NH}{{+\hfill \atop 4\hfill}}}$]]></tex-math><inline-graphic xlink:href="ark:/27927/pgh2cncsngm" mimetype="image" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /></alternatives></inline-formula> ions in the framework channel are off the channel axis. From 94 to 350 K the <inline-formula><alternatives><tex-math notation="tex"><![CDATA[${{\rm NH}{{+\hfill \atop 4\hfill}}}$]]></tex-math><inline-graphic xlink:href="ark:/27927/pgh2cncsnbd" mimetype="image" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /></alternatives></inline-formula> ion gradually approaches the channel axis and the related modulation of the framework and the hydrogen‐bond system occurs. The LT phase is simple antiferroelectric (AFE). The material becomes hexagonal above 355 K. In the high‐temperature (HT) phase, the Cu<sup>2+</sup> octahedron is compressed, and the <inline-formula><alternatives><tex-math notation="tex"><![CDATA[${{\rm NH}{{+\hfill \atop 4\hfill}}}$]]></tex-math><inline-graphic xlink:href="ark:/27927/pgh2cncsncz" mimetype="image" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /></alternatives></inline-formula> ions are arranged helically along the channel axis. Therefore, the phase transition is one from LT simple AFE to HT helical AFE. The temperature‐dependent structure evolution is accompanied by significant thermal and dielectric anomalies and anisotropic thermal expansion, due to the different status of the <inline-formula><alternatives><tex-math notation="tex"><![CDATA[${{\rm NH}{{+\hfill \atop 4\hfill}}}$]]></tex-math><inline-graphic xlink:href="ark:/27927/pgh2cncsndh" mimetype="image" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /></alternatives></inline-formula> ions and the framework modulations, and the structure–property relationship was established based on the extensive variable‐temperature single‐crystal structures. The material showed long range ordering of antiferromagnetism (AFM), with low dimensional character and a Néel temperature of 2.9 K. Therefore, within the material AFE and AFM orderings coexist in the low‐temperature region.</p> </abstract>