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

Cardenas, A.J.P.; O'Hagan, M.

doi:10.1107/S2056989016012251

research communications

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Volume 72| Part 9| September 2016| Pages 1290-1292

https://doi.org/10.1107/S2056989016012251

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

Allan Jay P. Cardenas ^a and Molly O'Hagan ^a ^*

^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.

Keywords: crystal structure; ionic liquid; electrolyte; hydrogen bond.

CCDC reference: 1496417

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 ): 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 ).

2. Structural commentary

The asymmetric unit consists of one bis(trifluoromethanesulfonyl)amide anion and one dimethylformamidium cation (Fig. 1): 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
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). 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 ). The C4—H⋯O2 distance is 2.57 Å (Table 1). 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	D⋯A	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) (Hou et al., 2014). 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) were isolated.

6. Refinement

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

Table 2
Experimental details

Crystal data
Chemical formula	C₃H₈NO⁺·C₂F₆NO₄S₂⁻
M_r	354.25
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	100
a, b, c (Å)	9.0254 (9), 11.4601 (12), 12.3621 (14)
V (Å³)	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 )
T_min, T_max	0.582, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	15926, 4274, 3989
R_int	0.033
(sin θ/λ)_max (Å⁻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
Δρ_max, Δρ_min (e Å⁻³)	0.29, −0.30
Absolute structure	Flack (1983 )
Absolute structure parameter	−0.01 (4)
Computer programs: APEX2 and SAINT (Bruker, 2013 ), SHELXS97 (Sheldrick, 2008 ), SHELXL2014 (Sheldrick, 2015 ) and OLEX2 (Dolomanov et al., 2009 ).

Supporting information

CCDC reference: 1496417

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989016012251/hb7586sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989016012251/hb7586Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2056989016012251/hb7586Isup3.cml

checkCIF report

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⁺·C₂F₆NO₄S₂⁻	D_x = 1.840 Mg m⁻³
M_r = 354.25	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, P2₁2₁2₁	Cell parameters from 9937 reflections
a = 9.0254 (9) Å	θ = 2.4–31.5°
b = 11.4601 (12) Å	µ = 0.51 mm⁻¹
c = 12.3621 (14) Å	T = 100 K
V = 1278.6 (2) Å³	Block, colourless
Z = 4	0.40 × 0.30 × 0.30 mm
F(000) = 712

Data collection top

Bruker APEXII CCD diffractometer	4274 independent reflections
Radiation source: fine-focus sealed tube	3989 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.033
φ and ω scans	θ_max = 31.7°, θ_min = 2.4°
Absorption correction: multi-scan (SADABS; Bruker, 2015)	h = −13→12
T_min = 0.582, T_max = 0.746	k = −16→16
15926 measured reflections	l = −17→18

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.025	H-atom parameters constrained
wR(F²) = 0.066	w = 1/[σ²(F_o²) + (0.0363P)²] where P = (F_o² + 2F_c²)/3
S = 1.06	(Δ/σ)_max = 0.001
4274 reflections	Δρ_max = 0.29 e Å⁻³
187 parameters	Δρ_min = −0.30 e Å⁻³
0 restraints	Absolute structure: Flack (1983)
Primary atom site location: structure-invariant direct methods	Absolute 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

	x	y	z	U_iso*/U_eq
S1	0.95481 (3)	0.01794 (3)	0.22331 (2)	0.02018 (7)
S2	1.05136 (3)	−0.05314 (3)	0.43097 (2)	0.01784 (6)
C3	1.44513 (14)	0.35694 (12)	0.10155 (11)	0.0239 (2)
H3A	1.3456	0.3670	0.0757	0.036*
H3B	1.5095	0.3401	0.0417	0.036*
H3C	1.4774	0.4272	0.1366	0.036*
F1	1.14157 (11)	−0.10684 (12)	0.11057 (9)	0.0507 (3)
F2	1.09712 (11)	0.15500 (8)	0.51280 (8)	0.0352 (2)
F3	0.97455 (13)	0.03798 (10)	0.61557 (7)	0.0455 (3)
F4	0.92510 (12)	−0.09329 (9)	0.04146 (7)	0.0428 (3)
F5	0.96239 (14)	−0.20423 (8)	0.17885 (9)	0.0472 (3)
F6	0.86942 (10)	0.11845 (9)	0.47659 (8)	0.0413 (2)
O1	0.80609 (10)	−0.00178 (9)	0.25752 (9)	0.0324 (3)
O2	0.99064 (13)	0.11860 (9)	0.16080 (8)	0.0338 (3)
O3	1.19216 (10)	−0.08639 (9)	0.47431 (8)	0.0276 (2)
O4	0.92949 (10)	−0.13268 (9)	0.43684 (8)	0.0250 (2)
N1	1.07837 (11)	0.00592 (10)	0.31584 (9)	0.0210 (2)
N2	1.44952 (11)	0.25990 (9)	0.17894 (8)	0.01757 (19)
O5	1.33633 (10)	0.11905 (9)	0.27429 (9)	0.0260 (2)
C1	0.99834 (15)	−0.10436 (13)	0.13368 (11)	0.0246 (3)
C2	0.99431 (14)	0.07208 (13)	0.51356 (11)	0.0253 (3)
C6	1.59693 (13)	0.22881 (13)	0.22087 (12)	0.0275 (3)
H6A	1.5879	0.1646	0.2703	0.041*
H6B	1.6389	0.2947	0.2578	0.041*
H6C	1.6602	0.2068	0.1618	0.041*
C4	1.33073 (12)	0.20433 (11)	0.20528 (10)	0.0193 (2)
H4	1.2405	0.2254	0.1747	0.023*
H5	1.265 (3)	0.0923 (19)	0.2902 (16)	0.051 (6)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
S1	0.02305 (12)	0.01838 (15)	0.01912 (13)	0.00063 (11)	−0.00390 (11)	0.00356 (11)
S2	0.01587 (10)	0.01937 (14)	0.01828 (12)	−0.00017 (10)	−0.00079 (10)	0.00504 (11)
C3	0.0222 (5)	0.0239 (7)	0.0257 (6)	−0.0006 (5)	0.0031 (5)	0.0054 (5)
F1	0.0329 (5)	0.0708 (8)	0.0485 (6)	0.0044 (5)	0.0119 (4)	−0.0170 (6)
F2	0.0436 (5)	0.0245 (5)	0.0374 (5)	−0.0066 (4)	−0.0092 (4)	−0.0004 (4)
F3	0.0703 (7)	0.0429 (6)	0.0232 (4)	−0.0029 (6)	0.0124 (5)	0.0005 (4)
F4	0.0657 (7)	0.0352 (5)	0.0276 (4)	−0.0002 (5)	−0.0181 (5)	−0.0046 (4)
F5	0.0837 (8)	0.0191 (4)	0.0389 (5)	−0.0046 (5)	0.0122 (6)	0.0027 (4)
F6	0.0301 (4)	0.0410 (6)	0.0530 (6)	0.0141 (4)	−0.0011 (4)	−0.0103 (5)
O1	0.0185 (4)	0.0475 (7)	0.0310 (5)	0.0074 (4)	−0.0046 (4)	0.0018 (5)
O2	0.0586 (7)	0.0185 (5)	0.0244 (5)	−0.0065 (5)	−0.0123 (5)	0.0063 (4)
O3	0.0198 (4)	0.0349 (6)	0.0282 (5)	0.0041 (4)	−0.0056 (4)	0.0067 (4)
O4	0.0234 (4)	0.0233 (5)	0.0282 (5)	−0.0052 (3)	0.0004 (4)	0.0070 (4)
N1	0.0199 (4)	0.0258 (6)	0.0174 (4)	−0.0036 (4)	−0.0020 (4)	0.0069 (4)
N2	0.0162 (4)	0.0197 (5)	0.0167 (4)	0.0011 (4)	0.0015 (4)	−0.0013 (4)
O5	0.0199 (4)	0.0285 (5)	0.0295 (5)	−0.0032 (4)	0.0019 (4)	0.0088 (4)
C1	0.0294 (5)	0.0225 (7)	0.0220 (6)	−0.0014 (5)	0.0003 (5)	0.0024 (5)
C2	0.0275 (5)	0.0252 (7)	0.0231 (6)	−0.0001 (5)	0.0006 (5)	0.0013 (5)
C6	0.0166 (5)	0.0322 (8)	0.0336 (7)	−0.0001 (5)	−0.0030 (5)	0.0034 (6)
C4	0.0172 (4)	0.0223 (6)	0.0184 (5)	−0.0003 (4)	0.0013 (4)	−0.0011 (5)

Geometric parameters (Å, º) top

S1—O1	1.4253 (10)	F2—C2	1.3282 (16)
S1—O2	1.4256 (11)	F3—C2	1.3321 (16)
S1—N1	1.6035 (11)	F4—C1	1.3239 (16)
S1—C1	1.8293 (15)	F5—C1	1.3141 (17)
S2—O3	1.4307 (9)	F6—C2	1.3273 (16)
S2—O4	1.4304 (9)	N2—C6	1.4716 (15)
S2—N1	1.5947 (11)	N2—C4	1.2888 (15)
S2—C2	1.8349 (15)	O5—C4	1.2983 (16)
C3—H3A	0.9600	O5—H5	0.74 (2)
C3—H3B	0.9600	C6—H6A	0.9600
C3—H3C	0.9600	C6—H6B	0.9600
C3—N2	1.4675 (16)	C6—H6C	0.9600
F1—C1	1.3242 (16)	C4—H4	0.9300

O1—S1—O2	120.18 (7)	C4—O5—H5	116.8 (16)
O1—S1—N1	115.44 (6)	F1—C1—S1	110.90 (11)
O1—S1—C1	105.10 (7)	F4—C1—S1	109.94 (10)
O2—S1—N1	107.36 (6)	F4—C1—F1	107.68 (12)
O2—S1—C1	104.06 (7)	F5—C1—S1	110.91 (10)
N1—S1—C1	102.53 (6)	F5—C1—F1	108.30 (13)
O3—S2—N1	108.15 (6)	F5—C1—F4	109.03 (13)
O3—S2—C2	104.43 (6)	F2—C2—S2	111.07 (9)
O4—S2—O3	119.62 (6)	F2—C2—F3	108.06 (11)
O4—S2—N1	115.68 (6)	F3—C2—S2	109.56 (10)
O4—S2—C2	104.73 (6)	F6—C2—S2	111.09 (9)
N1—S2—C2	101.98 (6)	F6—C2—F2	107.72 (12)
H3A—C3—H3B	109.5	F6—C2—F3	109.25 (12)
H3A—C3—H3C	109.5	N2—C6—H6A	109.5
H3B—C3—H3C	109.5	N2—C6—H6B	109.5
N2—C3—H3A	109.5	N2—C6—H6C	109.5
N2—C3—H3B	109.5	H6A—C6—H6B	109.5
N2—C3—H3C	109.5	H6A—C6—H6C	109.5
S2—N1—S1	124.53 (6)	H6B—C6—H6C	109.5
C3—N2—C6	115.95 (10)	N2—C4—O5	120.37 (11)
C4—N2—C3	121.11 (11)	N2—C4—H4	119.8
C4—N2—C6	122.92 (11)	O5—C4—H4	119.8

C3—N2—C4—O5	−179.64 (11)	O4—S2—N1—S1	21.78 (11)
O1—S1—N1—S2	14.69 (11)	O4—S2—C2—F2	−178.35 (9)
O1—S1—C1—F1	−169.55 (11)	O4—S2—C2—F3	62.34 (10)
O1—S1—C1—F4	71.48 (11)	O4—S2—C2—F6	−58.47 (11)
O1—S1—C1—F5	−49.18 (12)	N1—S1—C1—F1	−48.50 (12)
O2—S1—N1—S2	151.76 (9)	N1—S1—C1—F4	−167.47 (9)
O2—S1—C1—F1	63.26 (12)	N1—S1—C1—F5	71.88 (11)
O2—S1—C1—F4	−55.70 (11)	N1—S2—C2—F2	−57.43 (10)
O2—S1—C1—F5	−176.36 (10)	N1—S2—C2—F3	−176.74 (9)
O3—S2—N1—S1	159.07 (8)	N1—S2—C2—F6	62.45 (11)
O3—S2—C2—F2	55.11 (11)	C1—S1—N1—S2	−98.96 (9)
O3—S2—C2—F3	−64.20 (10)	C2—S2—N1—S1	−91.20 (9)
O3—S2—C2—F6	174.99 (10)	C6—N2—C4—O5	2.30 (19)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	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+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.

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