Monoprotonated species of 2-amino­malonyl difluoride, [C3H4F2NO2][H2F3]

Hollenwäger, D.; Leitz, D.; Bockmair, V.; Kornath, A.J.

doi:10.1107/S2053229624012452

research papers

STRUCTURAL
CHEMISTRY

ISSN: 2053-2296

Volume 81| Part 2| February 2025|

https://doi.org/10.1107/S2053229624012452

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Monoprotonated species of 2-aminomalonyl difluoride, [C₃H₄F₂NO₂][H₂F₃]

Dirk Hollenwäger,^a ^* Dominik Leitz,^a Valentin Bockmair ^a and Andreas J. Kornath ^a ‡

^aDepartment Chemie, Ludwig-Maximilians Universität, Butenandtstrasse 5-13 (Haus D), D-81377 München, Germany
^*Correspondence e-mail: dirk.hollenwaeger@cup.uni-muenchen.de

Edited by T. Ohhara, J-PARC Center, Japan Atomic Energy Agency, Japan (Received 4 October 2024; accepted 25 December 2024; online 8 January 2025)

The monoprotonated species of 2-aminomalonyl difluoride, namely, 1,3-difluoro-1,3-dioxopropan-2-aminium dihydrogen trifluoride, [C₃H₄F₂NO₂][H₂F₃], was synthesized from sulfur tetrafluoride in anhydrous hydrogen fluoride (aHF) with [NH₄][C₃H₅NO₄] as the starting material. The solvent was removed and the salt was dissolved in aHF and crystallized. In the solid state, the three-dimensional network is built by medium–strong N—H⋯F hydrogen bonds and C⋯F contacts. This is the first structure determination of an aminoacyl difluoride and the second of an aminoacyl fluoride.

Keywords: crystal structure; 2-aminomalonyl difluoride; aminoacyl fluoride; vibrational spectroscopy; sulfur tetrafluoride; complexone.

CCDC reference: 2413368

1. Introduction

The monoprotonated species of 2-aminomalonyl difluoride, as the [C₃H₄F₂NO₂][H₂F₃] salt, is the second characterized salt of an acylamino fluoride, after the synthesis of glycinoyl fluoride (Hollenwäger et al., 2024a ). Glycinoyl fluoride with protection groups was first characterized by NMR spectroscopy in 1999 by Carpino & Mansour (1999 ). The direct synthesis of acylamino fluorides was investigated by our group in 2024 (Hollenwäger et al., 2024a). The solid state of glycinoyl fluoride was characterized by vibrational and NMR spectroscopy, as well as single-crystal X-ray diffraction (Hollenwäger et al., 2024a). [C₃H₄F₂NO₂]⁺ is the first cation of the group of acyl fluorides which contains two acyl fluoride moieties. The direct synthesis with sulfur tetrafluoride in anhydrous hydrogen fluoride (aHF) applies Kollonitsch's idea of using HF as a solvent to improve the formation of SF₃⁺ to activate the deoxyfluorinating species (Kollonitsch et al., 1975 ). The aHF also performs the function of protonating the NH₂ group to prevent adduct formation of SF₄ with the lone pair of the nitrogen (Hollenwäger et al., 2024a; Goettel et al., 2012 ; Chaudhary et al., 2015 ). [C₃H₄F₂NO₂][H₂F₃] is produced with [NH₄][C₃H₅NO₄] as the starting material and belongs to the group of complexones (Hollenwäger et al., 2024b ; Anderegg et al., 2005 ). Due to the high toxicity of fluoride, its application is highly likely to be limited. The salt could be used in the specialized field of fluorine chemistry, as its two acyl fluoride moieties make it highly interesting for conversion in superacidic or Lewis acidic media.

2. Experimental

2.1. Synthesis and crystallization

[NH₄][C₃H₅NO₄] (67 mg, 0.893 mmol) was added in an FEP (fluorinated ethylene propylene) tube reactor. Anhydrous hydrogen fluoride (aHF, 0.75 ml) and sulfur tetrafluoride (203 mg, 1.87 mmol) were then added at −196 °C, and the mixture homogenized at room temperature. Excess solvent was removed at −78 °C overnight. The product was a colourless solid that was stable at room temperature. The equation of the formation is shown in Scheme 1.

2.2. Analysis (X-ray and Raman)

We investigated and characterized the [C₃H₄F₂NO₂][H₂F₃] salt by single-crystal X-ray diffraction and Raman spectroscopy. Complete data and the devices used for the X-ray measurements are listed in the supporting information (CIF file). Low-temperature Raman spectroscopic studies were performed using a Bruker MultiRAM FT–Raman spectrometer with Nd:YAG laser excitation (λ = 1064 cm⁻¹) under vacuum at −196 °C. For measurements, the synthesized compounds were transferred to a cooled glass cell.

2.3. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. The positions of the H atoms were identified by residual electron-density peaks on the difference Fourier map and by evaluation of the contacts (Fig. 1). Due to the high diffraction resolution, all H atoms were assigned with respect to the difference map and freely refined.

Table 1
Experimental details

Crystal data
Chemical formula	C₃H₃F₂NO₂⁺·H₂F₃⁻
M_r	183.09
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	102
a, b, c (Å)	5.5736 (2), 9.2154 (4), 12.7952 (7)
V (Å³)	657.20 (5)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.23
Crystal size (mm)	0.34 × 0.11 × 0.07

Data collection
Diffractometer	Rigaku Xcalibur Sapphire3
Absorption correction	Multi-scan (CrysAlis PRO; Rigaku OD, 2020 $[Rigaku OD (2020). CrysAlis PRO. Rigaku Oxford Diffraction Ltd, Yarnton, Oxfordshire, England.]$ )
T_min, T_max	0.945, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	7118, 2187, 1930
R_int	0.034
(sin θ/λ)_max (Å⁻¹)	0.752

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.034, 0.067, 1.02
No. of reflections	2187
No. of parameters	124
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.27, −0.18
Absolute structure	Flack x determined using 683 quotients [(I⁺) − (I⁻)]/[(I⁺) + (I⁻)] (Parsons et al., 2013 )
Absolute structure parameter	−0.3 (5)
Computer programs: CrysAlis PRO (Rigaku OD, 2020 $[Rigaku OD (2020). CrysAlis PRO. Rigaku Oxford Diffraction Ltd, Yarnton, Oxfordshire, England.]$ ), SHELXT (Sheldrick, 2015a ), SHELXL2019 (Sheldrick, 2015b ), ORTEP-3 for Windows (Farrugia, 2012 ) and PLATON (Spek, 2020 ).

Figure 1
A difference Fourier map of [C₃H₄F₂NO₂][H₂F₃] without the H atoms between F3, F4 and F5, and between N1 and F3, F4 and F5. The green solid lines and red dotted lines show positive and negative density distribution, respectively.

3. Results and discussion

3.1. Single-crystal X-ray diffraction

Herein we present the results of the single-crystal X-ray diffraction study of the salt [C₃H₄F₂NO₂][H₂F₃], namely, monoprotonated 2-aminomalonyl difluoride dihydrogen trifluoride. The salt crystallizes in the orthorhombic space group P2₁2₁2₁ with four formula units per unit cell. The asymmetric unit is shown in Fig. 2. The C1—C3 [1.518 (2) Å] and C2—C3 [1.519 (2) Å] bonds are shortened compared to those of the starting material [1.539 (2) and 1.549 (2) Å, respectively; Hollenwäger et al., 2024b]. The C—C bond lengths are elongated compared to the electron diffraction values of malonyl difluoride [1.502 (5) Å; Jin et al., 1992 ]. The C1—F1 bond length [1.331 (2) Å] is in the same range as the C2—F2 bond [1.329 (2) Å]. Compared to the C—F bond length of malonyl difluoride (Jin et al., 1992), the bond in [C₃H₄F₂NO₂][H₂F₃] [1.349 (4) Å] is slightly shortened. The C=O bonds [C1=O1 = 1.175 (2) Å and C1=O2 = 1.172 (2) Å] are in the same range as in malonyl difluoride [1.177 (3) Å; Jin et al., 1992]. The C3—N1 bond length [1.469 (2) Å] is significantly shortened with respect to the starting material [1.482 (2) Å], the Csp³—Nsp³ bond lengths (1.488 Å) in organic compounds and the bond in glycine [1.482 (3) Å; Hollenwäger et al., 2024b; Allen et al., 1987 ; Jiang et al., 2015 ]. Table 2 lists the bond lengths, bond angles and torsion angles of the [C₃H₄F₂NO₂][H₂F₃] salt, the starting material [NH₄][C₃H₅NO₄], glycinoyl fluoride, β-glycine and malonyl difluoride (Hollenwäger et al., 2024a,b; Jiang et al., 2015; Jin et al., 1992). The bond deviation of the crystal structure of [C₃H₄F₂NO₂][H₂F₃] with respect to malonyl difluoride results from the structure of malonyl difluoride being measured in the gas phase (Jin et al., 1992). The shortened C—C bond lengths of the [C₃H₄F₂NO₂][H₂F₃] salt compared to the [NH₄][C₃H₅NO₄] salt is a result of the stronger negative inductive effect of fluorine compared to oxygen in the carboxylic acid. Additionally, the starting material is a zwitterionic anion and the shown aminoacyl fluoride is a cationic salt. The determined structures of glycinoyl fluoride and [C₃H₄F₂NO₂][H₂F₃] are in good agreement with each other (Hollenwäger et al., 2024a). The second acyl fluoride moiety of [C₃H₄F₂NO₂][H₂F₃] also exerts a negative inductive effect on the backbone, whereby the C—C bonds are slightly lengthened compared to glycinoyl fluoride (Hollenwäger et al., 2024a).

Table 2
Bond lengths (Å), bond angles (°) and torsion angles (°) of [C₃H₄F₂NO₂][H₂F₃], [NH₄][C₃H₅NO₄], glycinoyl fluoride, β-glycine and malonyl difluoride

Bond length	[C₃H₄F₂NO₂][H₂F₃]	[NH₄][C₃H₅NO₄]	Glycinoyl fluoride	β-Glycine	Malonyl difluoride
C1—C3	1.518 (2)	1.5394 (18)	1.509 (5)	1.536 (3)	1.502 (5)
C2—C3	1.519 (2)	1.5485 (18)			1.502 (5)
C1—F1	1.331 (2)		1.333 (4)		1.349 (4)
C2—F2	1.329 (2)				1.349 (4)
C1=O1	1.175 (2)	1.2483 (16)		1.257 (2)	1.177 (3)
C2=O2	1.172 (2)	1.2462 (17)		1.258 (3)	1.177 (3)
C3—N1	1.469 (2)	1.4821 (16)	1.476 (5)	1.482 (3)

Angle
C1—C2—C3	114.1 (1)	113.00 (10)			110.2 (10)
C3—C1—O1	126.0 (2)	117.7 (1)	127.2 (3)		129.1 (8)
C3—C2—O2	125.9 (2)	116.9 (1)			129.1 (8)
C3—C1—F1	111.3 (1)		110.2 (3)		109.7 (7)
C3—C2—F2	111.4 (1)				109.7 (7)
N1—C3—C1	108.5 (1)	109.56 (10)	108.3 (3)	111.8 (1)
N1—C3—C2	108.6 (1)	109.98 (10)

Torsion angle
F1—C1—C3—N1	−173.5 (1)
F1—C1—C3—C2	65.4 (2)
O1—C1—C3—N1	4.7 (2)	−2.96 (16)	8.1 (5)
O1—C1—C3—C2	−116.4 (2)	120.0 (1)			112.0 (20)
F2—C2—C3—N1	177.7 (1)		−171.2 (3)
F2—C2—C3—C1	−61.2
O2—C2—C3—C1	122.4 (2)	−112.3 (1)			0.0

Figure 2
The asymmetric unit of [C₃H₄F₂NO₂][H₂F₃], with displacement ellipsoids drawn at the 50% probability level.

The C—C—C angle [114.1 (1)°] is significantly increased compared to both the starting material [113.0 (1)°] and malonyl difluoride [110.2 (10)°; Jin et al., 1992; Hollenwäger et al., 2024b]. The C—C—O angles [C3—C1—O1 = 126.0 (2)° and C3—C2—O2 = 125.9 (2)°] are significantly decreased compared to malonyl difluoride [129.1 (8)°; Jin et al., 1992]. The C—C—F angles [111.4 (1) and 111.3 (1)°] are significantly increased compared to malonyl difluoride [109.7 (7)°; Jin et al., 1992]. The C—C—N angles [N1—C3—C1 = 108.5 (1)° and N1—C3—C2 = 108.6 (1)°] are slightly decreased compared to the starting material (Hollenwäger et al., 2024b). The torsion angles are available in Table 2.

The crystal structure of [C₃H₄F₂NO₂][H₂F₃] results from a three-dimensional network (Fig. 3) of two strong hydrogen bonds within the [H₂F₃]⁻ anion [2.322 (2) Å for F4(—H5)⋯F3 and 2.338 (2) Å for F5(—H6)⋯F3] and three medium–strong hydrogen bonds classified according to Jeffrey (1997 ). The medium–strong hydrogen bonds connect the anion with the cation [2.655 (2) Å for N1(—H3)⋯F3, 2.742 (2) Å for N1(—H1)⋯F5 and 2.743 (2) Å for N1(—H2)⋯F4]. In addition, the network establishes three C⋯F contacts, which are within the van der Waals radii sum (3.17 Å) by approximately 16% [C1⋯F4 = 2.676 (2) Å, C1⋯F5 = 2.682 (2) Å and C2⋯F5 = 2.688 (2) Å]. The hydrogen bonds and C⋯F contacts are listed in the supporting information.

Figure 3
Hydrogen bonds in the crystal structure of [C₃H₄F₂NO₂][H₂F₃], with displacement ellipsoids drawn at the 50% probability level. [Symmetry codes: (i) −x + 1, y − $[{1\over 2}]$ , −z + $[{1\over 2}]$ ; (ii) x − 1, y, −z; (iii) −x + $[{1\over 2}]$ , −y + 1, z − $[{1\over 2}]$ ; (iv) −x + 1, y + $[{1\over 2}]$ , −z + $[{1\over 2}]$ ; (v) x + 1, y, z; (vi) −x + $[{1\over 2}]$ , −y + 1, z + $[{1\over 2}]$ ; (vii) x + $[{1\over 2}]$ , −y + $[{1\over 2}]$ , −z + 1; (viii) x − $[{1\over 2}]$ , −y + $[{1\over 2}]$ , −z + 1.]

3.2. Raman spectroscopy

The low-temperature Raman spectra of [C₃H₄F₂NO₂][H₂F₃], [NH₄][C₃H₅NO₄] and C₃H₄O₄ are illustrated in Fig. 4. Table 3 lists the Raman data for [C₃H₄F₂NO₂][H₂F₃] and the calculated frequencies for the [C₃H₄F₂NO₂]⁺ cation at the aug-cc-pVTZ level of theory. The first evidence of the successful preparation of the [C₃H₄F₂NO₂][H₂F₃] salt is the C=O valence oscillation being blue-shifted by approximately 193 cm⁻¹ to 1877 and 1846 cm⁻¹ compared to the starting material at 1684 cm⁻¹ (Hollenwäger et al., 2024b). The second pieces of evidence are the C—F valence oscillations, which are coupled with the δ(C—H) bands at 1303, 1235 and 1152 cm⁻¹. The C—C stretching vibrations are observed at 923 and 763 cm⁻¹. Only one of the three N—H vibrations is Raman-active and is observed at 3225 cm⁻¹. The C—H stretching oscillation is detected at 2978 cm⁻¹.

Table 3
Experimental (exptl) Raman vibrational frequencies (cm⁻¹) of [C₃H₄F₂NO₂][H₂F₃] and calculated (calc) Raman vibrational frequencies (cm⁻¹) of [C₃H₄NO₂F₂]⁺ at the M062x/aug-cc-pVTZ-level of theory (the scaling factor is 0.956)

Exptl	Calc	Assignment
	3327 (173)	A	ν1	ν(NH)
3225 (6)	3182 (251)	A	ν2	ν(NH)
	3143 (67)	A	ν3	ν(NH)
2978 (19)	2980 (22)	A	ν4	ν(CH)
1877 (100)	1889 (297)	A	ν5	ν(CO)
1846 (31)	1862 (210)	A	ν6	ν(CO)
1627 (14)	1578 (34)	A	ν7	δ(NH₂)
1611 (14)	1560 (44)	A	ν8	δ(NH₂)
1378 (19)	1446 (187)	A	ν9	δ(NH₂)
1303 (14)	1341 (251)	A	ν10	ν(CF)+δ(CH)
	1255 (98)	A	ν11	ν(CF)+δ(CH)
1235 (20)	1237 (208)	A	ν12	δ(CH)+ν(CF)
1152 (17)	1160 (59)	A	ν13	δ(CH)+ν(CF)
1133 (13)	1092 (43)	A	ν14	δ(CH)+δ(NH₃)
1083 (14)	1080 (8)	A	ν15	δ(CH)+δ(NH₃)
	1030 (16)	A	ν16	ν(CN)
923 (20)	895 (51)	A	ν17	ν(CC)
873 (47)	858 (25)	A	ν18	δ(CCC)
763 (77)	755 (1)	A	ν19	ν(CC)
657 (17)	650 (32)	A	ν20	δ(COF)
603 (20)	588 (3)	A	ν21	ρ(CCC)
587 (25)	576 (15)	A	ν22	δ(NH₃)
533 (15)
491 (36)
475 (32)	486 (47)		ν23	δ(NH₃)
439 (21)
402 (34)	380 (18)	A	ν24	δ(CCF)
352 (43)	303 (14)	A	ν25	δ(CCF)
248 (20)	287 (14)	A	ν26	δ(NH₃)
221 (41)
203 (32)	191 (0)	A	ν27	δ(NH₃)
155 (59)	160 (11)	A	ν28	δ(COF)
130 (55)
99 (46)	93 (14)	A	ν29	τ(COF)
90 (47)
80 (41)	45 (0)	A	ν30	τ(COF)

Figure 4
Low-temperature Raman spectra of [C₃H₄F₂NO₂][H₂F₃], [NH₄][C₃H₅NO₄] and malonic acid (C₃H₄O₄) (Hollenwäger et al., 2024b

4. Conclusion

Herein we present the first single-crystal X-ray diffraction and Raman spectroscopy study of the [C₃H₄F₂NO₂][H₂F₃] salt. This salt represents the first difluoride in the group of diacylamino fluorides and is a further example of a complexone.

Supporting information

CCDC reference: 2413368

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S2053229624012452/oj3024sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2053229624012452/oj3024Isup2.hkl

Computing details top

1,3-Difluoro-1,3-dioxopropan-2-aminium dihydrogen trifluoride top

Crystal data top

C₃H₃F₂NO₂⁺·H₂F₃⁻	D_x = 1.850 Mg m⁻³
M_r = 183.09	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, P2₁2₁2₁	Cell parameters from 2040 reflections
a = 5.5736 (2) Å	θ = 2.7–31.2°
b = 9.2154 (4) Å	µ = 0.23 mm⁻¹
c = 12.7952 (7) Å	T = 102 K
V = 657.20 (5) Å³	Needle, colorless
Z = 4	0.34 × 0.11 × 0.07 mm
F(000) = 368

Data collection top

Rigaku Xcalibur Sapphire3 diffractometer	2187 independent reflections
Radiation source: Enhance (Mo) X-ray Source	1930 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.034
Detector resolution: 15.9809 pixels mm^-1	θ_max = 32.3°, θ_min = 2.7°
ω scans	h = −8→5
Absorption correction: multi-scan (CrysAlis PRO; Rigaku OD, 2020)	k = −13→13
T_min = 0.945, T_max = 1.000	l = −19→18
7118 measured reflections

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.034	All H-atom parameters refined
wR(F²) = 0.067	w = 1/[σ²(F_o²) + (0.0296P)²] where P = (F_o² + 2F_c²)/3
S = 1.02	(Δ/σ)_max < 0.001
2187 reflections	Δρ_max = 0.27 e Å⁻³
124 parameters	Δρ_min = −0.18 e Å⁻³
0 restraints	Absolute structure: Flack x determined using 683 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.3 (5)

Special details top

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
F1	0.0476 (2)	0.32000 (12)	0.02215 (9)	0.0243 (3)
F2	0.4306 (2)	0.50434 (12)	0.05212 (8)	0.0244 (3)
O2	0.4408 (2)	0.58347 (13)	0.21402 (10)	0.0202 (3)
O1	−0.1665 (2)	0.31969 (15)	0.16660 (11)	0.0210 (3)
N1	0.2218 (3)	0.34495 (18)	0.29301 (12)	0.0171 (3)
C1	0.0210 (3)	0.33015 (19)	0.12529 (14)	0.0178 (3)
C2	0.3829 (3)	0.49451 (19)	0.15364 (13)	0.0160 (3)
C3	0.2606 (3)	0.35165 (19)	0.17959 (14)	0.0148 (3)
H1	0.154 (4)	0.257 (3)	0.3148 (19)	0.025 (6)*
H2	0.126 (4)	0.414 (2)	0.3121 (17)	0.020 (5)*
H4	0.362 (4)	0.275 (2)	0.1562 (15)	0.012 (5)*
H3	0.355 (4)	0.363 (3)	0.331 (2)	0.037 (7)*
F4	0.88392 (19)	0.54834 (12)	0.34615 (9)	0.0225 (2)
F5	0.53500 (19)	0.38358 (12)	0.59645 (9)	0.0221 (2)
F3	0.59728 (18)	0.39321 (12)	0.41590 (9)	0.0239 (3)
H5	0.784 (6)	0.482 (4)	0.378 (3)	0.071 (11)*
H6	0.562 (5)	0.385 (4)	0.524 (3)	0.070 (9)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
F1	0.0236 (5)	0.0276 (6)	0.0217 (5)	−0.0004 (4)	−0.0047 (5)	−0.0041 (5)
F2	0.0234 (5)	0.0291 (6)	0.0209 (6)	−0.0026 (5)	0.0059 (4)	0.0023 (4)
O2	0.0194 (6)	0.0165 (6)	0.0247 (7)	−0.0033 (5)	−0.0023 (5)	0.0009 (5)
O1	0.0136 (6)	0.0208 (7)	0.0287 (7)	−0.0012 (5)	−0.0019 (5)	−0.0008 (6)
N1	0.0138 (7)	0.0171 (7)	0.0203 (8)	−0.0019 (6)	−0.0009 (6)	0.0030 (6)
C1	0.0185 (8)	0.0120 (8)	0.0227 (8)	0.0006 (6)	−0.0043 (6)	−0.0010 (7)
C2	0.0110 (7)	0.0176 (8)	0.0195 (8)	0.0006 (6)	0.0005 (6)	0.0027 (7)
C3	0.0120 (7)	0.0135 (8)	0.0188 (8)	0.0013 (6)	−0.0014 (6)	−0.0004 (6)
F4	0.0201 (5)	0.0205 (6)	0.0268 (6)	−0.0018 (4)	0.0006 (5)	−0.0004 (5)
F5	0.0238 (5)	0.0232 (6)	0.0193 (5)	0.0051 (4)	0.0010 (4)	0.0032 (4)
F3	0.0210 (5)	0.0301 (6)	0.0206 (5)	−0.0046 (4)	−0.0020 (4)	−0.0012 (5)

Geometric parameters (Å, º) top

F1—C1	1.331 (2)	C1—C3	1.518 (2)
F2—C2	1.329 (2)	C2—C3	1.519 (2)
O2—C2	1.172 (2)	C3—H4	0.95 (2)
O1—C1	1.175 (2)	F4—H5	0.92 (4)
N1—C3	1.469 (2)	F5—H6	0.94 (3)
N1—H1	0.94 (2)	F3—H5	1.41 (4)
N1—H2	0.87 (2)	F3—H6	1.40 (3)
N1—H3	0.90 (3)

C1···F4	2.676 (2)	C2···F5	2.688 (2)
C1···F5	2.682 (2)

C3—N1—H1	112.9 (15)	O2—C2—C3	125.85 (16)
C3—N1—H2	109.8 (14)	F2—C2—C3	111.25 (14)
H1—N1—H2	107.6 (19)	N1—C3—C1	108.51 (14)
C3—N1—H3	113.6 (15)	N1—C3—C2	108.57 (14)
H1—N1—H3	109 (2)	C1—C3—C2	114.07 (14)
H2—N1—H3	103 (2)	N1—C3—H4	111.5 (12)
O1—C1—F1	122.64 (16)	C1—C3—H4	106.3 (12)
O1—C1—C3	125.94 (17)	C2—C3—H4	107.9 (12)
F1—C1—C3	111.40 (14)	H5—F3—H6	118.6 (19)
O2—C2—F2	122.80 (16)

O1—C1—C3—N1	4.7 (3)	O2—C2—C3—N1	1.3 (2)
F1—C1—C3—N1	−173.50 (14)	F2—C2—C3—N1	177.71 (13)
O1—C1—C3—C2	−116.4 (2)	O2—C2—C3—C1	122.37 (19)
F1—C1—C3—C2	65.34 (19)	F2—C2—C3—C1	−61.17 (18)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···F5ⁱ	0.94 (2)	1.84 (2)	2.7422 (19)	159 (2)
N1—H2···F4ⁱⁱ	0.87 (2)	1.88 (2)	2.7426 (19)	172 (2)
N1—H3···F3	0.90 (3)	1.75 (3)	2.6551 (19)	174 (2)
F4—H5···F3	0.92 (4)	1.41 (4)	2.3221 (15)	170 (3)
F5—H6···F3	0.94 (3)	1.40 (3)	2.3378 (16)	177 (3)
N1—H1···F5ⁱ	0.94 (2)	1.84 (2)	2.7422 (19)	159 (2)
N1—H2···F4ⁱⁱ	0.87 (2)	1.88 (2)	2.7426 (19)	172 (2)
N1—H3···F3	0.90 (3)	1.75 (3)	2.6551 (19)	174 (2)
F4—H5···F3	0.92 (4)	1.41 (4)	2.3221 (15)	170 (3)
F5—H6···F3	0.94 (3)	1.40 (3)	2.3378 (16)	177 (3)

Symmetry codes: (i) x−1/2, −y+1/2, −z+1; (ii) x−1, y, z.

Bond lengths (Å), bond angles (°) and torsion angles (°) of [C₃H₄F₂NO₂][H₂F₃], [NH₄][C₃H₅NO₄], glycinoyl fluoride, β-glycine and malonyl difluoride top

Bond length	[C₃H₄F₂NO₂][H₂F₃]	[NH₄][C₃H₅NO₄]	Glycinoyl fluoride	β-Glycine	Malonyl difluoride
C1—C3	1.518 (2)	1.5394 (18)	1.509 (5)	1.536 (3)	1.502 (5)
C2—C3	1.519 (2)	1.5485 (18)			1.502 (5)
C1—F1	1.331 (2)		1.333 (4)		1.349 (4)
C2—F2	1.329 (2)				1.349 (4)
C1═O1	1.175 (2)	1.2483 (16)		1.257 (2)	1.177 (3)
C2═O2	1.172 (2)	1.2462 (17)		1.258 (3)	1.177 (3)
C3—N1	1.469 (2)	1.4821 (16)	1.476 (5)	1.482 (3)

Angle
C1—C2—C3	114.1 (1)	113.00 (10)			110.2 (10)
C3—C1—O1	126.0 (2)	117.7 (1)	127.2 (3)		129.1 (8)
C3—C2—O2	125.9 (2)	116.9 (1)			129.1 (8)
C3—C1—F1	111.3 (1)		110.2 (3)		109.7 (7)
C3—C2—F2	111.4 (1)				109.7 (7)
N1—C3—C1	108.5 (1)	109.56 (10)	108.3 (3)	111.8 (1)
N1—C3—C2	108.6 (1)	109.98 (10)

Torsion angle
F1—C1—C3—N1	-173.5 (1)
F1—C1—C3—C2	65.4 (2)
O1—C1—C3—N1	4.7 (2)	-2.96 (16)	8.1 (5)
O1—C1—C3—C2	-116.4 (2)	120.0 (1)			112.0 (20)
F2—C2—C3—N1	177.7 (1)		-171.2 (3)
F2—C2—C3—C1	-61.2
O2—C2—C3—C1	122.4 (2)	-112.3 (1)			0.0

Experimental (exptl) Raman vibrational frequencies (cm^-1) of [C₃H₄F₂NO₂][H₂F₃] and calculated (calc) Raman vibrational frequencies (cm^-1) of [C₃H₄NO₂F₂]⁺ at the M062x/aug-cc-pVTZ-level of theory (the scaling factor is 0.956) [Please provide suitable headings for columns 3 and 4] top

Exptl	Calc	???	???	Assignment
	3327 (173)	A	ν1	ν(NH)
3225 (6)	3182 (251)	A	ν2	ν(NH)
	3143 (67)	A	ν3	ν(NH)
2978 (19)	2980 (22)	A	ν4	ν(CH)
1877 (100)	1889 (297)	A	ν5	ν(CO)
1846 (31)	1862 (210)	A	ν6	ν(CO)
1627 (14)	1578 (34)	A	ν7	δ(NH₂)
1611 (14)	1560 (44)	A	ν8	δ(NH₂)
1378 (19)	1446 (187)	A	ν9	δ(NH₂)
1303 (14)	1341 (251)	A	ν10	ν(CF)+δ(CH)
	1255 (98)	A	ν11	ν(CF)+δ(CH)
1235 (20)	1237 (208)	A	ν12	δ(CH)+ν(CF)
1152 (17)	1160 (59)	A	ν13	δ(CH)+ν(CF)
1133 (13)	1092 (43)	A	ν14	δ(CH)+δ(NH₃)
1083 (14)	1080 (8)	A	ν15	δ(CH)+δ(NH₃)
	1030 (16)	A	ν16	ν(CN)
923 (20)	895 (51)	A	ν17	ν(CC)
873 (47)	858 (25)	A	ν18	δ(CCC)
763 (77)	755 (1)	A	ν19	ν(CC)
657 (17)	650 (32)	A	ν20	δ(COF)
603 (20)	588 (3)	A	ν21	ρ(CCC)
587 (25)	576 (15)	A	ν22	δ(NH₃)
533 (15)
491 (36)
475 (32)	486 (47)		ν23	δ(NH₃)
439 (21)
402 (34)	380 (18)	A	ν24	δ(CCF)
352 (43)	303 (14)	A	ν25	δ(CCF)
248 (20)	287 (14)	A	ν26	δ(NH₃)
221 (41)
203 (32)	191 (0)	A	ν27	δ(NH₃)
155 (59)	160 (11)	A	ν28	δ(COF)
130 (55)
99 (46)	93 (14)	A	ν29	τ(COF)
90 (47)
80 (41)	45 (0)	A	ν30	τ(COF)

Footnotes

‡Deceased

Acknowledgements

We are grateful to the Department of Chemistry at the Ludwig Maximilian University of Munich, the Deutsche Forschungsgemeinschaft (DFG), the F-Select GmbH, and Professor Dr Karaghiosoff and Dr Constantin Hoch for their support. Open access funding enabled and organized by Projekt DEAL.

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