Low-Melting Imidazolium-Based Salts with the Paramagnetic Reineckate-Analogue Anion [Cr(NCS) 4 (bipy)] − (bipy = 2,2′- Bipyridine): Syntheses, Properties, and Structures Tim Peppel, †,‡ Philipp Thiele, † Mei-Bo Tang, § Jing-Tai Zhao,* ,∥ and Martin Kö ckerling* ,† † Department of Inorganic Solid State Chemistry, University of Rostock, Albert-Einstein-Strasse 3a, D-18059 Rostock, Germany § Shanghai Institute of Ceramics, Chinece Academy of Sciences, Shanghai 200050, P. R. China ∥ School of Materials Science and Engineering, Shanghai University, No. 99 Shangda Road, Shanghai 200072, P. R. China ABSTRACT: In order to investigate the potential ionic liquid properties of Reineckate- analogue materials, four new salts, consisting of the heteroleptic [Cr(NCS) 4 (bipy)] − complex anion and imidazolium-based cations A + = 1-ethyl-3-methylimidazolium, 1-n-butyl- 3-methylimidazolium, pentamethylimidazolium, and 1,3-dimethyl-2,4,5-triphenylimidazo- lium, were investigated. Their structures were established by single-crystal X-ray diffraction. The compounds are paramagnetic with effective magnetic moments in the range of those expected by the number of unpaired spins of the chromium(III) ion. All melting points are above 100 °C, which prevents us from calling these compounds “ionic liquids”. Nevertheless, they are low for salts of this constitution and may be useful for molten salt reactions. Cyclic voltammetry measurements show no reversible electron-transfer steps. ■ INTRODUCTION Salts containing the diamminetetra(isothiocyanato)chromate- (III) anion [Cr(NCS) 4 (NH 3 ) 2 ] − (Reineckate anion) are among the earliest known chromium(III) complexes and have been known for more than 150 years. 1−5 Since then, Reineckates and related compounds have been developed as useful chemical actinometers, substances for quantum yield determinations, and compounds in charge-transfer photo- chemistry. 6−13 Reineckates have also been used in the analysis of medical products. 14 In addition, Reineckate-analogue complexes bearing [Cr(NCS) 4 L] − anions [L = 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen)] have shown their ability in the analytical determination of alkaloids 15 and chloroquine (drug for malaria prevention and treatment), 16 in the analytical determination of bismuth, 17 and as promising magnetic charge- transfer salts. 18 Recently, we have reported on a series of imidazolium-based Reineckates in order to investigate their properties with respect to ionic liquids (ILs). 19 ILs, salts with melting points below 100 °C, have attracted great interest because of their special and useful properties, such as wide liquid ranges, negligible vapor pressures, large electrochemical windows, or high electric conductivities. 20−22 Some transition-metal-based ILs (magnetic ILs) exhibit interesting magnetic properties in addition. 23−25 In this contribution, we report on the syntheses, properties, and structures of a series of imidazolium-based salts with Reineckate-analogue anions [Cr(NCS) 4 (bipy)] − . Four new Reineckate-analogue compounds with the [Cr(NCS) 4 (bipy)] − anion and the imidazolium-based cations EMIm (1-ethyl-3- methylimidazolium; 1), n BMIm (1-n-butyl-3-methylimidazo- lium; 2), PeMIm (pentamethylimidazolium; 3), and DML (1,3- dimethyllophinium or 1,3-dimethyl-2,4,5-triphenylimidazolium; 4) were synthesized and investigated. The crystal and molecular structures were determined by single-crystal X-ray diffraction (XRD). Magnetic data at room temperature of all substances were obtained using NMR techniques. The temperature dependence of the magnetism was measured for (EMIm)[Cr- (NCS) 4 (bipy)] by means of a Physical Property Measurement System (PPMS) magnetometer in the temperature range of 10−300 K. Furthermore, cyclic voltammetry (CV) measure- ments and differential scanning calorimetry (DSC) measure- ments were performed. ■ EXPERIMENTAL SECTION Materials. All commercially available starting materials were obtained from Sigma-Aldrich. Their stated purity was at least 99%. They were used without further purification or drying. 1-Ethyl-3- methylimidazolium bromide (EMImBr) and 1-n-butyl-3-methylimida- zolium bromide ( n BMImBr) were synthesized according to known procedures. 26 Elem anal. Found (calcd) for EMImBr (C 6 H 11 N 2 Br): C, 37.85 (37.72); H, 6.04 (5.80); N, 14.48 (14.66). Mp: 77 °C (lit. 27 77 °C). 1 H NMR (DMSO-d 6 ): δ 1.48 (t, 3H, Me), 4.00 (s, 3H, N−Me), 4.29 (q, 2H, N−CH 2 −), 7.56 (s, 2H, N−CH−CH−N), 10.17 (s, 1H, N− CH−N). 13 C NMR (DMSO-d 6 ): δ 15.8 (Me), 36.7 (N-Me), 45.3 (N−CH 2 −), 122.1 (N−CH−CH−N), 123.8 (N−CH−CH−N), 136.9 (N−CH−N). Special Issue: To Honor the Memory of Prof. John D. Corbett Received: September 28, 2014 Published: December 22, 2014 Article pubs.acs.org/IC © 2014 American Chemical Society 982 DOI: 10.1021/ic502358b Inorg. Chem. 2015, 54, 982−988