(1‐Butyl‐4‐methyl‐pyridinium)[Cu(SCN)2]: A Coordination Polymer and Ionic Liquid. Issue 18 (18th March 2014)

• Record Type: Journal Article
• Authors: Eike T. Spielberg, ; Edengeiser, Eugen; Mallick, Bert; Havenith, Martina; Mudring, Anja‐Verena
• Is Part Of: Chemistry. Volume 20:Issue 18(2014)
• Page Start: 5338
• Page End: 5345
• Publication Date: 2014-03-18
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201302777
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>The compound (C<sub>4</sub>C<sub>1</sub>py)[Cu(SCN)<sub>2</sub>], (C<sub>4</sub>C<sub>1</sub>py=1‐Butyl‐4‐methyl‐pyridinium), which can be obtained from CuSCN and the ionic liquid (C<sub>4</sub>C<sub>1</sub>py)(SCN), turns out to be a new organic–inorganic hybrid material as it qualifies both, as a coordination polymer and an ionic liquid. It features linked [Cu(SCN)<sub>2</sub>]<sup>−</sup> units, in which the thiocyanates bridge the copper ions in a μ<sub>1, 3</sub>‐fashion. The resulting one‐dimensional chains run along the <italic>a</italic> axis, separated by the C<sub>4</sub>C<sub>1</sub>py counterions. Powder X‐ray diffraction not only confirms the single‐crystal X‐ray structure solution but proves the reformation of the coordination polymer from an isotropic melt. However, the materials shows a complex thermal behavior often encountered for ionic liquids such as a strong tendency to form a supercooled melt. At a relatively high cooling rate, glass formation is observed. When heating this melt in differential scanning calorimetry (DSC) and temperature‐dependent polarizing optical microscopy (POM), investigations reveal the existence of a less thermodynamically stable crystalline polymorph. Raman measurements conducted at 10 and 100 °C point towards the formation of polyanionic chain fragments in the melt. Solid‐state UV/Vis spectroscopy shows a broad absorption band around 18 870 cm<sup>−1</sup> (530 nm) and another strong one below 20 000 cm<sup>−1</sup> (<500 nm). The latter is attributed to the d(Cu<sup>I</sup>)→π*(SCN)‐MLCT (metal‐to‐ligand charge transfer) transition within the coordination polymer yielding an energy gap of 2.4 eV. At room temperature and upon irradiation with UV light, the material shows a weak fluorescence band at 15 870 cm<sup>−1</sup> (630 nm) with a quantum efficiency of 0.90(2) % and a lifetime of 131(2) ns. Upon lowering the temperature, the luminescence intensity strongly increases. Simultaneously, the band around 450 nm in the excitation spectrum decreases.</p> </abstract>