Mixed metal double salt ionic liquids comprised of [HN222]2[ZnCl4] and AlCl3 provide tunable Lewis acid catalysts related to the ionic environmentCCDC 1585681 and 1585682. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c8dt00976g

Two solids of differing Lewis acidities, triethylammonium tetrachlorozincate ([HN 222 ] 2 [ZnCl 4 ]) and AlCl 3 , have been combined across 0.1 to 0.9 mole fractions (with respect to [HN 222 ] 2 [ZnCl 4 ]), and homogeneous solid double salts or mixed metal [HN 222 ] 2 x [(1 − x )AlCl 3 + x ZnCl 4 ] double salt ionic liquids (DSILs) were obtained at x = 0.33, 0.4, and 0.5 with varying Lewis acidities. The characterization of the prepared DSILs (melting point, color, homogeneity, 1 H, 13 C, and 27 Al nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (IR), single crystal X-ray diffraction (SCXRD), and matrix-assisted laser-desorption ionization time-of-flight (MALDI-TOF) mass spectrometry) suggests that [HN 222 ] 2 [ZnCl 4 ] transfers Cl − from [ZnCl 4 ] 2− to the stronger Lewis acid AlCl 3 , forming intermediate acidic DSILs with [AlCl 4 ] − and [Al 2 Cl 7 ] − anions and mixed anionic Zn species. Qualitative Lewis acidity measurements using acetonitrile as an IR-active probe showed that the acidity of the DSILs decreased as the amount of [ZnCl 4 ] 2− increased. In a Beckman rearrangement reaction of acetophenone oxime, significant catalytic activity was observed for the DSIL at x = 0.33, where the activity of the DSIL was found to be even higher than [HN 222 ][Al 2 Cl 7 ], AlCl 3 , [HN 222 ] 2 [ZnCl 4 ], or ZnCl 2 despite its lower Lewis acidity, apparently due to the synergistic effect of AlCl 3 and [ZnCl 4 ] 2− as Cl − donors for the formation of catalytically active species. The findings illustrate a DSIL-based approach for modifying the catalytic activity of a known complex without changing its inner coordination sphere. Tunable acidic mixed-metal double salt ionic liquids (DSILs), [HN 222 ] 2 x [(1 − x )AlCl 3 + x ZnCl 4 ], were prepared by mixing [HN 222 ] 2 [ZnCl 4 ] with AlCl 3 , and found to have unique and controllable catalytic activities.