J Chem Crystallogr (2009) 39:662–668
663
absence of any strong interaction between the anion and
cation may help explain the low melting points of these salts.
In general, the triflimide anions here prefer transoid
conformations. Only in rare cases, such as 1,3-dimethylim-
idazolium [14], 1-(1-(ethoxycarbonyl)ethyl)-3-methylimida-
zolium [15], 1-ethyl-3-methylimidazolium [19], and 1-hex-
ylpyridinium [23] salts, the triflimide anion adopts a cisoid
conformation in organic salts. Analysis of 143 triflimide data
from the CSD (without disordered structures) revealed the
presence of 83 transoid and 60 cisoid structures (more
precisely 45 synperiplanar, 15 synclinal, 12 anticlinal, 71
antiperiplanar). A torsion angle of 170 5° is preferred in
the majority (45 out of 143) of the structures as shown in
Fig. 1. All CSD (version 5.29, Jan 2008, 436384 entries)
searches were performed using Conquest 1.10. Notably,
orientational disorder of triflimide ions in crystal structures is
not uncommon [2, 11, 23, 27]. This disordering may con-
tribute to the low melting points as well.
mentioned that the corresponding acid, bis(trifluoromethyl-
sulfonyl)amide, exhibits bifurcated N–HÁÁÁO hydrogen
bonds [10, 30].
Here, we report three crystal structures of new, low
melting, protic organic triflimide salts with different
hydrogen bonding motifs.
Experimental Section
NMR spectra were recorded with a Bruker AC 300 spec-
trometer. IR spectra were obtained with a Nicolet 5700 FT
instrument. The crystal structures were determined using
Nonius KappaCCD and STOE IPDS 2 diffractometers,
respectively. The experimental conditions and crystallo-
graphic data are listed in Table 1. X-Ray diffraction data
were collected with graphite-monochromated Mo Ka
˚
radiation (k = 0.71073 A). The structures were solved
Recently, protic ionic liquids (PILs) [28] have been rec-
ognized as an interesting class of ILs. A convenient method
of preparation of PILs by protonation of 1-alkylimidazoles
using Tf2NH has been proposed [29]. In protic salts more
interactions between the ions are to be expected. However, in
the few crystalline examples known, no unexpected net-
works or direct contacts to the triflimide nitrogen atom have
been detected. Thus, in trimethylammonium [26] and
ammonium triflimide [13], the cations again participate in
weak hydrogen bonding with two of the sulfonyl oxygen
atoms. Surprisingly, in one of the structures of N,N,N-tri-
methylglycine triflimide [11], solely cationic interactions
were seen. For the sake of completeness, it should be
using direct methods and refined by full-matrix least-
squares techniques. All non-hydrogen atoms were assigned
anisotropic displacement parameters in the refinement. The
structures were refined on F2 using SHELXTL-97 [31].
The crystallographic data have been deposited with the
Cambridge Crystallographic Data Center, under reference
CCDC 686015–686017.
1,3-Diamino-2-Methylimidazolium
Bis(trifluoromethylsulfonyl)imide (1)
A mixture of 1,3-diamino-2-methylimidazolium chloride
[32] (1.20 g, 8.2 mmol) and LiNTf2 (2.36 g, 8.2 mmol) in
H2O (20 mL) was ultrasonicated for 5 min. The precipitate
was filtered and dried over P2O5. Yield: 1.2 g (26%). M.p.
58–59 °C. IR (neat): 3,384, 3,308, 3,144, 1,644, 1,565,
1,353, 1,323, 1,182, 1,131, 1,051, 919, 797, 736, 729, 644,
1
608, 569, 515 cm-1. H NMR (DMSO-d6): 2.49 (s, 3H),
6.56 (br), 7.46 (s, 2H) ppm. 13C NMR (DMSO-d6): 8.1,
119.5 (q, 2C, J = 325 Hz), 120.9 (2C), 144.4 ppm.
1,3-Dihydroxy-2-Methylimidazolium
Bis(trifluoromethylsulfonyl)imide (2)
A mixture of Tf2NH (35.9 g, 128 mmol) and of 1-hydroxy-
2-methylimidazole 3-oxide [33] (14.6 g, 128 mmol) was
heated to 80 °C, causing the mixture to liquefy. After
stirring for 1 h, the reaction mixture was allowed to cool to
room temperature, giving 50.5 g (100%) of crystalline
product. M.p. 72 °C. IR (neat): 3,323, 3,152, 2,797, 1,364,
1
1,354, 1,184, 1,132, 1,052, 793, 748, 714, 605 cm-1. H
NMR (DMSO-d6): 2.48 (s, 3H), 7.86 (s, 2H), 13.5 (br, 2H)
ppm. 13C NMR (DMSO-d6): 7.1, 117.4 (2C), 119.5 (q, 2C,
J = 321 Hz), 136.6 ppm.
Fig. 1 Polar histogram showing the distribution of C–SÁÁÁS–C torsion
angles in known crystalline triflimides
123