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Crystal structure of di­methyl­formamidium bis­­(tri­fluoro­methane­sulfon­yl)amide: an ionic liquid

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aPacific Northwest National Laboratory, PO Box 999 MSIN: K2-57, Richland, WA 99352, USA
*Correspondence e-mail: Molly.OHagan@pnnl.gov

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 14 May 2016; accepted 27 July 2016; online 12 August 2016)

At 100 K, the title mol­ecular salt, C3H8NO+·C2F6NO4S2, has ortho­rhom­bic (P212121) symmetry; the amino H atom of bis­(tri­fluoro­methane­sulfon­yl)amine (HNTf2) was transferred to the basic O atom of di­methyl­formamide (DMF) when the ionic liquid components were mixed. The structure displays an O—H⋯N hydrogen bond, which links the cation to the anion, which is reinforced by a non-conventional C—H⋯O inter­action, generating an R22(7) loop. A further very weak C—H⋯O inter­action generates an [001] chain.

1. Chemical context

A ionic liquid, also known as a liquid electrolyte, is a salt or an ion pair that remains in a liquid state below 373 K (Ghandi, 2014[Ghandi, K. (2014). Green Sustainable Chem. 4, 44-53.]): such species extend the selection of solvents or media of chemical processes. The study of its solid-state structure can facilitate the exploration of other inter­molecular forces of attraction besides electrostatic forces that govern the properties of these ionic liquids such as melting point, acidity, ion mobility, diffusion and viscosity. In this study we report the crystal structure of an organic liquid salt formed by a proton-transfer reaction between bis­(tri­fluoro­methane­sulfon­yl)amine and di­methyl­formamide. This protic ionic liquid has been used as a solvent, an electrolyte and a substrate for electrocatalysis (Hou et al., 2014[Hou, J., Fang, M., Cardenas, A. J. P., Shaw, W. J., Helm, M. L., Bullock, R. M., Roberts, J. A. S. & O'Hagan, M. (2014). Energ. Environ. Sci. 7, 4013-4017.]).

[Scheme 1]

2. Structural commentary

The asymmetric unit consists of one bis­(tri­fluoro­methane­sulfon­yl)amide anion and one di­methyl­formamidium cation (Fig. 1[link]): when the components were mixed, the acidic N—H proton of HNTf2 was transfered to the formyl group of di­methyl­formamide. The di­methyl­formamidium C4—O5 and N2—C4 bond lengths are 1.2983 (16) and 1.2888 (15) Å respectively, which reflect the delocalization of charge via π-electrons. The N2—C4—O5 angle does not deviate from the expected 120° of an sp2-hybridized carbon atom [120.37 (11)°]. The bis­(tri­fluoro­methane­sulfon­yl)amide anion features S1—N1 and S2—N1 bond distances of 1.6035 (11) and 1.5947 (11) Å, respectively.

[Figure 1]
Figure 1
The mol­ecular structure of the title compound, showing displacement ellipsoids drawn at the 50% probability level. Hydrogen bonds are shown as dashed lines.

3. Supra­molecular features

The ion pair features two hydrogen bonds (Table 1[link]). One is between the acidic hydrogen atom attached to the formyl oxygen atom of the di­methyl­formamidium cation and the nitro­gen atom of the bis­(tri­fluoro­methane­sulfon­yl)amide anion: the H⋯N distance is 1.98 (3) Å. The other is a non-conventional C—H⋯O hydrogen bond between the formyl hydrogen atom of the di­methyl­formamidium cation and one of the sulfoxide oxygen atoms of the anion (Desiraju, 1991[Desiraju, G. R. (1991). Acc. Chem. Res. 24, 290-296.]). The C4—H⋯O2 distance is 2.57 Å (Table 1[link]). Together, these generate an R22(7) loop. A further very weak C—H⋯O inter­action links the ion pairs into an [001] chain.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
O5—H5⋯N1 0.74 (3) 1.98 (3) 2.7139 (14) 172 (2)
C4—H4⋯O2 0.93 2.57 3.2694 (16) 132
C4—H4⋯O4i 0.93 2.63 3.4773 (16) 152
Symmetry code: (i) [-x+2, y+{\script{1\over 2}}, -z+{\script{1\over 2}}].

4. Database survey

A CSD search (Web CSD version 1.1.1; May 4, 2016) found no structures that have the same ion pairing. Some structures feature the same bis­(tri­fluoro­methane­sulfon­yl)amide anion but different cations, which are usually metal complexes.

5. Synthesis and crystallization

A literature procedure was followed to synthesize [(DMF)H]NTf2 (I)[link] (Hou et al., 2014[Hou, J., Fang, M., Cardenas, A. J. P., Shaw, W. J., Helm, M. L., Bullock, R. M., Roberts, J. A. S. & O'Hagan, M. (2014). Energ. Environ. Sci. 7, 4013-4017.]). Equimolar amounts of of di­methyl­formamide (17.6 mmol, 1.29 g) and bis­(tri­fluoro­methane­sulfon­yl)amine (17.8 mmol, 5.0g) were mixed tog­ether after cooling each reagent to 238 K. The solution was stirred at room temperature until it formed a light-yellow viscous solution. The solution was then left to stand undisturbed at room temperature and colorless blocks of (I)[link] were isolated.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2[link]. H atoms were positioned geometrically and allowed to ride on their parent atoms: C—H = 0.93–0.96 Å with Uiso(H) = 1.5Ueq(C-meth­yl) and 1.2Ueq(C) for other H atoms. The methyl groups were refined as rotating groups.

Table 2
Experimental details

Crystal data
Chemical formula C3H8NO+·C2F6NO4S2
Mr 354.25
Crystal system, space group Orthorhombic, P212121
Temperature (K) 100
a, b, c (Å) 9.0254 (9), 11.4601 (12), 12.3621 (14)
V3) 1278.6 (2)
Z 4
Radiation type Mo Kα
μ (mm−1) 0.51
Crystal size (mm) 0.40 × 0.30 × 0.30
 
Data collection
Diffractometer Bruker APEXII CCD
Absorption correction Multi-scan (SADABS; Bruker, 2015[Bruker (2015). SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.])
Tmin, Tmax 0.582, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections 15926, 4274, 3989
Rint 0.033
(sin θ/λ)max−1) 0.739
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.025, 0.066, 1.06
No. of reflections 4274
No. of parameters 187
H-atom treatment H-atom parameters constrained
Δρmax, Δρmin (e Å−3) 0.29, −0.30
Absolute structure Flack (1983[Flack, H. D. (1983). Acta Cryst. A39, 876-881.])
Absolute structure parameter −0.01 (4)
Computer programs: APEX2 and SAINT (Bruker, 2013[Bruker (2013). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]), SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]), SHELXL2014 (Sheldrick, 2015[Sheldrick, G. M. (2015). Acta Cryst. C71, 3-8.]) and OLEX2 (Dolomanov et al., 2009[Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339-341.]).

Supporting information


Computing details top

Data collection: APEX2 (Bruker, 2013); cell refinement: SAINT (Bruker, 2013); data reduction: SAINT (Bruker, 2013); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Dimethylformamidium bis(trifluoromethanesulfonyl)amide top
Crystal data top
C3H8NO+·C2F6NO4S2Dx = 1.840 Mg m3
Mr = 354.25Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, P212121Cell parameters from 9937 reflections
a = 9.0254 (9) Åθ = 2.4–31.5°
b = 11.4601 (12) ŵ = 0.51 mm1
c = 12.3621 (14) ÅT = 100 K
V = 1278.6 (2) Å3Block, colourless
Z = 40.40 × 0.30 × 0.30 mm
F(000) = 712
Data collection top
Bruker APEXII CCD
diffractometer
4274 independent reflections
Radiation source: fine-focus sealed tube3989 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.033
φ and ω scansθmax = 31.7°, θmin = 2.4°
Absorption correction: multi-scan
(SADABS; Bruker, 2015)
h = 1312
Tmin = 0.582, Tmax = 0.746k = 1616
15926 measured reflectionsl = 1718
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.025H-atom parameters constrained
wR(F2) = 0.066 w = 1/[σ2(Fo2) + (0.0363P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.06(Δ/σ)max = 0.001
4274 reflectionsΔρmax = 0.29 e Å3
187 parametersΔρmin = 0.30 e Å3
0 restraintsAbsolute structure: Flack (1983)
Primary atom site location: structure-invariant direct methodsAbsolute structure parameter: 0.01 (4)
Special details top

Experimental. Absorption correction: SADABS-2014/5 (Bruker,2014/5) was used for absorption correction. wR2(int) was 0.0777 before and 0.0530 after correction. The Ratio of minimum to maximum transmission is 0.7795. The λ/2 correction factor is 0.00150.

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2sigma(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
S10.95481 (3)0.01794 (3)0.22331 (2)0.02018 (7)
S21.05136 (3)0.05314 (3)0.43097 (2)0.01784 (6)
C31.44513 (14)0.35694 (12)0.10155 (11)0.0239 (2)
H3A1.34560.36700.07570.036*
H3B1.50950.34010.04170.036*
H3C1.47740.42720.13660.036*
F11.14157 (11)0.10684 (12)0.11057 (9)0.0507 (3)
F21.09712 (11)0.15500 (8)0.51280 (8)0.0352 (2)
F30.97455 (13)0.03798 (10)0.61557 (7)0.0455 (3)
F40.92510 (12)0.09329 (9)0.04146 (7)0.0428 (3)
F50.96239 (14)0.20423 (8)0.17885 (9)0.0472 (3)
F60.86942 (10)0.11845 (9)0.47659 (8)0.0413 (2)
O10.80609 (10)0.00178 (9)0.25752 (9)0.0324 (3)
O20.99064 (13)0.11860 (9)0.16080 (8)0.0338 (3)
O31.19216 (10)0.08639 (9)0.47431 (8)0.0276 (2)
O40.92949 (10)0.13268 (9)0.43684 (8)0.0250 (2)
N11.07837 (11)0.00592 (10)0.31584 (9)0.0210 (2)
N21.44952 (11)0.25990 (9)0.17894 (8)0.01757 (19)
O51.33633 (10)0.11905 (9)0.27429 (9)0.0260 (2)
C10.99834 (15)0.10436 (13)0.13368 (11)0.0246 (3)
C20.99431 (14)0.07208 (13)0.51356 (11)0.0253 (3)
C61.59693 (13)0.22881 (13)0.22087 (12)0.0275 (3)
H6A1.58790.16460.27030.041*
H6B1.63890.29470.25780.041*
H6C1.66020.20680.16180.041*
C41.33073 (12)0.20433 (11)0.20528 (10)0.0193 (2)
H41.24050.22540.17470.023*
H51.265 (3)0.0923 (19)0.2902 (16)0.051 (6)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
S10.02305 (12)0.01838 (15)0.01912 (13)0.00063 (11)0.00390 (11)0.00356 (11)
S20.01587 (10)0.01937 (14)0.01828 (12)0.00017 (10)0.00079 (10)0.00504 (11)
C30.0222 (5)0.0239 (7)0.0257 (6)0.0006 (5)0.0031 (5)0.0054 (5)
F10.0329 (5)0.0708 (8)0.0485 (6)0.0044 (5)0.0119 (4)0.0170 (6)
F20.0436 (5)0.0245 (5)0.0374 (5)0.0066 (4)0.0092 (4)0.0004 (4)
F30.0703 (7)0.0429 (6)0.0232 (4)0.0029 (6)0.0124 (5)0.0005 (4)
F40.0657 (7)0.0352 (5)0.0276 (4)0.0002 (5)0.0181 (5)0.0046 (4)
F50.0837 (8)0.0191 (4)0.0389 (5)0.0046 (5)0.0122 (6)0.0027 (4)
F60.0301 (4)0.0410 (6)0.0530 (6)0.0141 (4)0.0011 (4)0.0103 (5)
O10.0185 (4)0.0475 (7)0.0310 (5)0.0074 (4)0.0046 (4)0.0018 (5)
O20.0586 (7)0.0185 (5)0.0244 (5)0.0065 (5)0.0123 (5)0.0063 (4)
O30.0198 (4)0.0349 (6)0.0282 (5)0.0041 (4)0.0056 (4)0.0067 (4)
O40.0234 (4)0.0233 (5)0.0282 (5)0.0052 (3)0.0004 (4)0.0070 (4)
N10.0199 (4)0.0258 (6)0.0174 (4)0.0036 (4)0.0020 (4)0.0069 (4)
N20.0162 (4)0.0197 (5)0.0167 (4)0.0011 (4)0.0015 (4)0.0013 (4)
O50.0199 (4)0.0285 (5)0.0295 (5)0.0032 (4)0.0019 (4)0.0088 (4)
C10.0294 (5)0.0225 (7)0.0220 (6)0.0014 (5)0.0003 (5)0.0024 (5)
C20.0275 (5)0.0252 (7)0.0231 (6)0.0001 (5)0.0006 (5)0.0013 (5)
C60.0166 (5)0.0322 (8)0.0336 (7)0.0001 (5)0.0030 (5)0.0034 (6)
C40.0172 (4)0.0223 (6)0.0184 (5)0.0003 (4)0.0013 (4)0.0011 (5)
Geometric parameters (Å, º) top
S1—O11.4253 (10)F2—C21.3282 (16)
S1—O21.4256 (11)F3—C21.3321 (16)
S1—N11.6035 (11)F4—C11.3239 (16)
S1—C11.8293 (15)F5—C11.3141 (17)
S2—O31.4307 (9)F6—C21.3273 (16)
S2—O41.4304 (9)N2—C61.4716 (15)
S2—N11.5947 (11)N2—C41.2888 (15)
S2—C21.8349 (15)O5—C41.2983 (16)
C3—H3A0.9600O5—H50.74 (2)
C3—H3B0.9600C6—H6A0.9600
C3—H3C0.9600C6—H6B0.9600
C3—N21.4675 (16)C6—H6C0.9600
F1—C11.3242 (16)C4—H40.9300
O1—S1—O2120.18 (7)C4—O5—H5116.8 (16)
O1—S1—N1115.44 (6)F1—C1—S1110.90 (11)
O1—S1—C1105.10 (7)F4—C1—S1109.94 (10)
O2—S1—N1107.36 (6)F4—C1—F1107.68 (12)
O2—S1—C1104.06 (7)F5—C1—S1110.91 (10)
N1—S1—C1102.53 (6)F5—C1—F1108.30 (13)
O3—S2—N1108.15 (6)F5—C1—F4109.03 (13)
O3—S2—C2104.43 (6)F2—C2—S2111.07 (9)
O4—S2—O3119.62 (6)F2—C2—F3108.06 (11)
O4—S2—N1115.68 (6)F3—C2—S2109.56 (10)
O4—S2—C2104.73 (6)F6—C2—S2111.09 (9)
N1—S2—C2101.98 (6)F6—C2—F2107.72 (12)
H3A—C3—H3B109.5F6—C2—F3109.25 (12)
H3A—C3—H3C109.5N2—C6—H6A109.5
H3B—C3—H3C109.5N2—C6—H6B109.5
N2—C3—H3A109.5N2—C6—H6C109.5
N2—C3—H3B109.5H6A—C6—H6B109.5
N2—C3—H3C109.5H6A—C6—H6C109.5
S2—N1—S1124.53 (6)H6B—C6—H6C109.5
C3—N2—C6115.95 (10)N2—C4—O5120.37 (11)
C4—N2—C3121.11 (11)N2—C4—H4119.8
C4—N2—C6122.92 (11)O5—C4—H4119.8
C3—N2—C4—O5179.64 (11)O4—S2—N1—S121.78 (11)
O1—S1—N1—S214.69 (11)O4—S2—C2—F2178.35 (9)
O1—S1—C1—F1169.55 (11)O4—S2—C2—F362.34 (10)
O1—S1—C1—F471.48 (11)O4—S2—C2—F658.47 (11)
O1—S1—C1—F549.18 (12)N1—S1—C1—F148.50 (12)
O2—S1—N1—S2151.76 (9)N1—S1—C1—F4167.47 (9)
O2—S1—C1—F163.26 (12)N1—S1—C1—F571.88 (11)
O2—S1—C1—F455.70 (11)N1—S2—C2—F257.43 (10)
O2—S1—C1—F5176.36 (10)N1—S2—C2—F3176.74 (9)
O3—S2—N1—S1159.07 (8)N1—S2—C2—F662.45 (11)
O3—S2—C2—F255.11 (11)C1—S1—N1—S298.96 (9)
O3—S2—C2—F364.20 (10)C2—S2—N1—S191.20 (9)
O3—S2—C2—F6174.99 (10)C6—N2—C4—O52.30 (19)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O5—H5···N10.74 (3)1.98 (3)2.7139 (14)172 (2)
C4—H4···O20.932.573.2694 (16)132
C4—H4···O4i0.932.633.4773 (16)152
Symmetry code: (i) x+2, y+1/2, z+1/2.
 

Acknowledgements

This research was supported as part of the Center for Mol­ecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences.

References

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