organic compounds
(R)-1-Phenylethylammonium trifluoroacetate
aEscuela de Ingeniería Química, Universidad del Istmo, Ciudad Universitaria s/n, 70760 Sto. Domingo Tehuantepec, Oax., Mexico, and bDEP Facultad de Ciencias Químicas, UANL, Guerrero y Progreso S/N, Col. Treviño, 64570 Monterrey, NL, Mexico
*Correspondence e-mail: sylvain_bernes@Hotmail.com
In the 8H12N+·C2F3O2−, all of the ammonium H atoms serve as donors for hydrogen bonds to carboxylate O atoms, forming an R43(10) ring motif based on two cations and two anions. Since both cations and anions act as inter-ion bridging groups, R(10) rings aggregate in a one-dimensional supramolecular network by sharing the strongest N—H⋯O bond. Edge-sharing motifs lie on the twofold screw axis parallel to [010], and antiparallel packing of these 21-column structural units results in the This arrangement is one of the most commonly occurring in conglomerates of chiral 1-phenylethylamine with achiral monocarboxylic acids, confirming that these ionic salts are particularly robust supramolecular heterosynthons useful in crystal engineering.
of the title salt, CRelated literature
For graph-set analysis, see: Etter (1990); Bernstein et al. (1995). For characteristic structural patterns found in crystal salts of 1-phenylethylamine and monocarboxylic acids, see: Kinbara, Hashimoto et al. (1996); Kinbara, Kai et al. (1996); Lemmerer et al. (2008). For related chiral salt structures, see: Johansen et al. (1998); Boussac et al. (2002); Lemmerer et al. (2008).
Experimental
Crystal data
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Data collection
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Refinement
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Data collection: XSCANS (Siemens, 1996); cell XSCANS; data reduction: XSCANS (Siemens, 1996); program(s) used to solve structure: SHELXTL-Plus (Sheldrick, 2008); program(s) used to refine structure: SHELXTL-Plus; molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXTL-Plus.
Supporting information
https://doi.org/10.1107/S1600536810013565/pb2025sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536810013565/pb2025Isup2.hkl
The title salt crystallized when attempting to synthesize a diimine organic ligand. A mixture of (S)-6-acetyloxy-5-methyl-2,3-hexanedione (1 g, 5.37 mmol) and Na2SO4 (4 g) in chloroform (10 ml) was stirred for 5 min. A catalytic amount of trifluoroacetic acid and 2 equiv. of (R)-(+)-α-phenylethylamine (10.6 mmol) were added and the mixture was refluxed (ca. 353 K) under inert atmosphere, until starting materials were not detected by TLC (ca. 2 h). After evaporation under reduced pressure, the crude was recrystallized from CH2Cl2 at 298 K, affording, among other products, the title salt.
As no heavy atoms are present in the crystal and data were measured at room-temperature using Mo Kα radiation, no absorption correction was applied to the raw data. Because of insufficient effects, the could not be reliably determined, and measured Friedel pairs (796) were merged. was assigned by reference to the chiral amine used as starting material, assuming that no inversion occurred during crystallization. Ammonium H atoms were refined with free coordinates, in order to get accurate dimensions for hydrogen bonds. Other H atoms were placed in idealized positions and refined as riding to their carrier atoms, with bond lengths fixed to 0.93 (aromatic CH), 0.96 (methyl CH3) or 0.98 Å (methine CH). Isotropic displacement parameters for H atoms were calculated as Uiso(H) = 1.2Ueq(C) for aromatic CH groups and Uiso(H) = 1.5Ueq(C, N) for other groups. The methyl group was considered as a rigid group free to rotate about its C—C bond.
In their works about
of conglomerates, Kinbara et al. noted that characteristic hydrogen-bond networks were formed in the salt crystals of 1-phenylethylamine and 1-(4-isopropylphenyl)ethylamine with cinnamic acid (Kinbara, Kai et al., 1996). They suggested that "the pattern of hydrogen bonds plays a significant role in the formation of conglomerates" (Kinbara, Hashimoto et al., 1996). In the specific case of salts of chiral 1-phenylethylamine with achiral monocarboxylic acids, a number of structural determinations indeed showed that two predominant supramolecular arrangements are favored by the charge assisted N—H···O hydrogen bonds, which result in crystals belonging to P21 or P212121 space groups (Lemmerer et al., 2008): cations and anions associate through quite strong hydrogen bonds to form C21(4)C22(6)[R43(10)] motifs (Etter, 1990; Bernstein et al., 1995). This basic unit has hydrogen bonds with translational units, forming an infinite columnar structure, which generates a screw axis in the (invariably a 21 axis). This supramolecular structure, referred as '21–column' in the Kinbara's reports, may be arranged in a parallel packing in the crystal, which then belongs to P21 or in an antiparallel fashion, generating P212121 crystals.The chiral title salt (Fig. 1) clearly falls in the latter category. Both the cation and anion are placed in general positions in an orthorhombic → R65(16) → R87(22) → R109(28) → ··· → R2n2n-1(6n-2) [with n > 1]. The shortest contact between neighboring 21–columns is N1—H1B···F2i, which should be regarded as a van der Waals contact rather than as an actual hydrogen bond. As a consequence, an antiparallel arrangement of 21–columns is favored (Fig. 2, inset), which is, in turn, reflected in the P212121 Such crystal structures were obtained for numerous 1-phenylethylamine salts including different anions, e.g. bromofluoroacetate (Boussac et al., 2002), m-iodobenzoate (Lemmerer et al., 2008) or more complex, bulky carboxylate derivatives (Johansen et al., 1998).
All ammonium H atoms form hydrogen bonds with carboxylate O atoms, giving a ring motif R43(10), as shown in Fig. 2. The strongest hydrogen bond, N1—H1C···O2ii is common to two rings motifs. The repetition of the motif in the [010] direction generates homochiral (R)–21–columns. This 1D supramolecular network includes larger ring motifs, which appear if shared contacts are omitted. The sequence of sub-rings nest is R43(10)The above description is thus in line with expectations from previous reported structures, and confirms that salts based on chiral 1-phenylethylamine and achiral monocarboxylic acids are robust heterosynthons, useful for crystal engineering and
prediction. The feature should however not been transferred to other salts (or worse, to cocrystals) of 1-phenylethylamine, which stabilize different supramolecular motifs, if any.For graph-set analysis, see: Etter (1990); Bernstein et al. (1995). For characteristic structural patterns found in crystal salts of 1-phenylethylamine and monocarboxylic acids, see: Kinbara, Hashimoto et al. (1996); Kinbara, Kai et al. (1996); Lemmerer et al. (2008). For related chiral salt structures, see: Johansen et al. (1998); Boussac et al. (2002); Lemmerer et al. (2008).
Data collection: XSCANS (Siemens, 1996); cell
XSCANS (Siemens, 1996); data reduction: XSCANS (Siemens, 1996); program(s) used to solve structure: SHELXTL-Plus (Sheldrick, 2008); program(s) used to refine structure: SHELXTL-Plus (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXTL-Plus (Sheldrick, 2008).C8H12N+·C2F3O2− | F(000) = 488 |
Mr = 235.21 | Dx = 1.352 Mg m−3 |
Orthorhombic, P212121 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2ac 2ab | Cell parameters from 70 reflections |
a = 6.7821 (5) Å | θ = 4.5–12.5° |
b = 6.9887 (8) Å | µ = 0.13 mm−1 |
c = 24.378 (2) Å | T = 298 K |
V = 1155.49 (19) Å3 | Prism, colorless |
Z = 4 | 0.60 × 0.44 × 0.40 mm |
Siemens P4 diffractometer | Rint = 0.020 |
Radiation source: fine-focus sealed tube | θmax = 29.0°, θmin = 1.7° |
Graphite monochromator | h = −9→4 |
2θ/ω scans | k = −9→1 |
3079 measured reflections | l = −33→1 |
1808 independent reflections | 3 standard reflections every 97 reflections |
1288 reflections with I > 2σ(I) | intensity decay: 1% |
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)] = 0.041 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.112 | w = 1/[σ2(Fo2) + (0.0464P)2 + 0.1579P] where P = (Fo2 + 2Fc2)/3 |
S = 1.03 | (Δ/σ)max < 0.001 |
1808 reflections | Δρmax = 0.16 e Å−3 |
156 parameters | Δρmin = −0.13 e Å−3 |
0 restraints | Extinction correction: SHELXTL-Plus (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 constraints | Extinction coefficient: 0.045 (4) |
Primary atom site location: structure-invariant direct methods |
C8H12N+·C2F3O2− | V = 1155.49 (19) Å3 |
Mr = 235.21 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 6.7821 (5) Å | µ = 0.13 mm−1 |
b = 6.9887 (8) Å | T = 298 K |
c = 24.378 (2) Å | 0.60 × 0.44 × 0.40 mm |
Siemens P4 diffractometer | Rint = 0.020 |
3079 measured reflections | 3 standard reflections every 97 reflections |
1808 independent reflections | intensity decay: 1% |
1288 reflections with I > 2σ(I) |
R[F2 > 2σ(F2)] = 0.041 | 0 restraints |
wR(F2) = 0.112 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.03 | Δρmax = 0.16 e Å−3 |
1808 reflections | Δρmin = −0.13 e Å−3 |
156 parameters |
x | y | z | Uiso*/Ueq | ||
N1 | 0.9254 (3) | 0.1712 (3) | 0.19995 (7) | 0.0480 (4) | |
H1C | 1.002 (5) | 0.206 (4) | 0.2286 (11) | 0.072* | |
H1B | 0.853 (5) | 0.062 (5) | 0.2039 (11) | 0.072* | |
H1A | 0.840 (5) | 0.268 (5) | 0.1966 (11) | 0.072* | |
C1 | 1.0532 (3) | 0.1429 (4) | 0.15044 (8) | 0.0513 (5) | |
H1 | 1.1377 | 0.0316 | 0.1571 | 0.062* | |
C2 | 1.1846 (5) | 0.3153 (5) | 0.14290 (11) | 0.0818 (9) | |
H2C | 1.2617 | 0.3000 | 0.1102 | 0.123* | |
H2B | 1.2709 | 0.3273 | 0.1739 | 0.123* | |
H2A | 1.1049 | 0.4283 | 0.1398 | 0.123* | |
C3 | 0.9260 (3) | 0.1001 (4) | 0.10055 (8) | 0.0502 (5) | |
C4 | 0.9482 (5) | −0.0721 (4) | 0.07311 (11) | 0.0706 (7) | |
H4 | 1.0390 | −0.1616 | 0.0857 | 0.085* | |
C5 | 0.8359 (6) | −0.1118 (5) | 0.02695 (12) | 0.0893 (10) | |
H5 | 0.8526 | −0.2272 | 0.0086 | 0.107* | |
C6 | 0.7020 (5) | 0.0165 (5) | 0.00854 (11) | 0.0819 (10) | |
H6 | 0.6265 | −0.0114 | −0.0223 | 0.098* | |
C7 | 0.6776 (4) | 0.1863 (5) | 0.03497 (10) | 0.0743 (8) | |
H7 | 0.5859 | 0.2744 | 0.0221 | 0.089* | |
C8 | 0.7891 (4) | 0.2282 (4) | 0.08117 (9) | 0.0633 (7) | |
H8 | 0.7710 | 0.3442 | 0.0992 | 0.076* | |
C9 | 0.6937 (4) | 0.6770 (3) | 0.19540 (9) | 0.0482 (5) | |
O1 | 0.6911 (4) | 0.5019 (3) | 0.19191 (10) | 0.0921 (7) | |
O2 | 0.8190 (3) | 0.7849 (3) | 0.21505 (7) | 0.0620 (5) | |
C10 | 0.5086 (4) | 0.7725 (4) | 0.17224 (11) | 0.0613 (6) | |
F1 | 0.4723 (3) | 0.7214 (4) | 0.12145 (7) | 0.1175 (8) | |
F2 | 0.5178 (3) | 0.9610 (2) | 0.17221 (11) | 0.1065 (8) | |
F3 | 0.3482 (2) | 0.7254 (3) | 0.20053 (8) | 0.0914 (6) |
U11 | U22 | U33 | U12 | U13 | U23 | |
N1 | 0.0484 (10) | 0.0459 (9) | 0.0498 (9) | −0.0030 (9) | −0.0118 (9) | 0.0002 (9) |
C1 | 0.0420 (10) | 0.0574 (13) | 0.0545 (11) | 0.0045 (11) | −0.0077 (10) | −0.0010 (10) |
C2 | 0.0655 (16) | 0.105 (2) | 0.0744 (16) | −0.029 (2) | −0.0104 (14) | 0.0154 (17) |
C3 | 0.0429 (11) | 0.0622 (13) | 0.0455 (10) | 0.0012 (12) | −0.0017 (9) | 0.0003 (10) |
C4 | 0.0760 (17) | 0.0669 (16) | 0.0689 (14) | 0.0113 (16) | −0.0136 (15) | −0.0104 (13) |
C5 | 0.116 (3) | 0.082 (2) | 0.0699 (15) | −0.003 (2) | −0.0199 (18) | −0.0186 (16) |
C6 | 0.085 (2) | 0.106 (3) | 0.0544 (13) | −0.022 (2) | −0.0162 (15) | −0.0043 (16) |
C7 | 0.0650 (16) | 0.099 (2) | 0.0585 (13) | 0.0027 (18) | −0.0157 (13) | 0.0114 (15) |
C8 | 0.0618 (14) | 0.0706 (16) | 0.0576 (12) | 0.0107 (14) | −0.0108 (12) | −0.0038 (12) |
C9 | 0.0487 (12) | 0.0465 (12) | 0.0495 (10) | 0.0049 (10) | −0.0017 (10) | −0.0005 (9) |
O1 | 0.0946 (16) | 0.0488 (11) | 0.1330 (18) | 0.0160 (11) | −0.0199 (16) | −0.0080 (11) |
O2 | 0.0575 (10) | 0.0609 (10) | 0.0677 (9) | −0.0061 (9) | −0.0241 (8) | 0.0114 (8) |
C10 | 0.0477 (13) | 0.0611 (14) | 0.0753 (14) | −0.0048 (13) | −0.0089 (12) | 0.0110 (13) |
F1 | 0.1021 (14) | 0.173 (2) | 0.0768 (10) | −0.0089 (18) | −0.0389 (10) | 0.0115 (13) |
F2 | 0.0614 (10) | 0.0583 (10) | 0.200 (2) | 0.0064 (9) | −0.0258 (13) | 0.0349 (11) |
F3 | 0.0526 (8) | 0.0911 (13) | 0.1303 (14) | −0.0024 (10) | 0.0155 (9) | 0.0106 (12) |
N1—C1 | 1.499 (3) | C5—C6 | 1.352 (5) |
N1—H1C | 0.90 (3) | C5—H5 | 0.9300 |
N1—H1B | 0.92 (3) | C6—C7 | 1.361 (4) |
N1—H1A | 0.90 (3) | C6—H6 | 0.9300 |
C1—C2 | 1.510 (4) | C7—C8 | 1.388 (3) |
C1—C3 | 1.521 (3) | C7—H7 | 0.9300 |
C1—H1 | 0.9800 | C8—H8 | 0.9300 |
C2—H2C | 0.9600 | C9—O1 | 1.227 (3) |
C2—H2B | 0.9600 | C9—O2 | 1.233 (3) |
C2—H2A | 0.9600 | C9—C10 | 1.530 (3) |
C3—C8 | 1.374 (3) | C10—F1 | 1.312 (3) |
C3—C4 | 1.385 (3) | C10—F2 | 1.319 (3) |
C4—C5 | 1.387 (4) | C10—F3 | 1.329 (3) |
C4—H4 | 0.9300 | ||
C1—N1—H1C | 109.1 (18) | C5—C4—H4 | 119.8 |
C1—N1—H1B | 106.6 (18) | C6—C5—C4 | 120.4 (3) |
H1C—N1—H1B | 117 (2) | C6—C5—H5 | 119.8 |
C1—N1—H1A | 113.5 (18) | C4—C5—H5 | 119.8 |
H1C—N1—H1A | 104 (2) | C5—C6—C7 | 120.2 (3) |
H1B—N1—H1A | 107 (2) | C5—C6—H6 | 119.9 |
N1—C1—C2 | 109.5 (2) | C7—C6—H6 | 119.9 |
N1—C1—C3 | 109.99 (17) | C6—C7—C8 | 120.1 (3) |
C2—C1—C3 | 113.23 (19) | C6—C7—H7 | 119.9 |
N1—C1—H1 | 108.0 | C8—C7—H7 | 119.9 |
C2—C1—H1 | 108.0 | C3—C8—C7 | 120.7 (3) |
C3—C1—H1 | 108.0 | C3—C8—H8 | 119.7 |
C1—C2—H2C | 109.5 | C7—C8—H8 | 119.7 |
C1—C2—H2B | 109.5 | O1—C9—O2 | 130.3 (3) |
H2C—C2—H2B | 109.5 | O1—C9—C10 | 113.4 (2) |
C1—C2—H2A | 109.5 | O2—C9—C10 | 116.2 (2) |
H2C—C2—H2A | 109.5 | F1—C10—F2 | 106.3 (2) |
H2B—C2—H2A | 109.5 | F1—C10—F3 | 105.6 (2) |
C8—C3—C4 | 118.3 (2) | F2—C10—F3 | 106.6 (3) |
C8—C3—C1 | 122.0 (2) | F1—C10—C9 | 112.6 (2) |
C4—C3—C1 | 119.7 (2) | F2—C10—C9 | 113.4 (2) |
C3—C4—C5 | 120.4 (3) | F3—C10—C9 | 111.85 (19) |
C3—C4—H4 | 119.8 | ||
N1—C1—C3—C8 | 61.4 (3) | C4—C3—C8—C7 | −0.6 (4) |
C2—C1—C3—C8 | −61.5 (3) | C1—C3—C8—C7 | 178.9 (2) |
N1—C1—C3—C4 | −119.1 (2) | C6—C7—C8—C3 | 0.4 (4) |
C2—C1—C3—C4 | 118.0 (3) | O1—C9—C10—F1 | −54.5 (3) |
C8—C3—C4—C5 | 0.7 (4) | O2—C9—C10—F1 | 126.5 (2) |
C1—C3—C4—C5 | −178.8 (3) | O1—C9—C10—F2 | −175.2 (3) |
C3—C4—C5—C6 | −0.7 (5) | O2—C9—C10—F2 | 5.8 (3) |
C4—C5—C6—C7 | 0.5 (5) | O1—C9—C10—F3 | 64.2 (3) |
C5—C6—C7—C8 | −0.4 (5) | O2—C9—C10—F3 | −114.8 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1A···O1 | 0.90 (3) | 1.92 (3) | 2.812 (3) | 171 (3) |
N1—H1B···O2i | 0.92 (3) | 1.97 (3) | 2.818 (3) | 154 (3) |
N1—H1C···O2ii | 0.90 (3) | 1.92 (3) | 2.816 (2) | 175 (3) |
N1—H1B···F2i | 0.92 (3) | 2.50 (3) | 3.202 (3) | 134 (2) |
Symmetry codes: (i) x, y−1, z; (ii) −x+2, y−1/2, −z+1/2. |
Experimental details
Crystal data | |
Chemical formula | C8H12N+·C2F3O2− |
Mr | 235.21 |
Crystal system, space group | Orthorhombic, P212121 |
Temperature (K) | 298 |
a, b, c (Å) | 6.7821 (5), 6.9887 (8), 24.378 (2) |
V (Å3) | 1155.49 (19) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.13 |
Crystal size (mm) | 0.60 × 0.44 × 0.40 |
Data collection | |
Diffractometer | Siemens P4 |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3079, 1808, 1288 |
Rint | 0.020 |
(sin θ/λ)max (Å−1) | 0.682 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.041, 0.112, 1.03 |
No. of reflections | 1808 |
No. of parameters | 156 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.16, −0.13 |
Computer programs: XSCANS (Siemens, 1996), SHELXTL-Plus (Sheldrick, 2008), Mercury (Macrae et al., 2008).
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1A···O1 | 0.90 (3) | 1.92 (3) | 2.812 (3) | 171 (3) |
N1—H1B···O2i | 0.92 (3) | 1.97 (3) | 2.818 (3) | 154 (3) |
N1—H1C···O2ii | 0.90 (3) | 1.92 (3) | 2.816 (2) | 175 (3) |
Symmetry codes: (i) x, y−1, z; (ii) −x+2, y−1/2, −z+1/2. |
Acknowledgements
This work was supported by CONACyT (grant 83049).
References
Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl. 34, 1555–1573. CrossRef CAS Web of Science Google Scholar
Boussac, H., Crassous, J., Dutasta, J.-P., Grosvalet, L. & Thozet, A. (2002). Tetrahedron Asymmetry, 13, 975–981. Web of Science CSD CrossRef CAS Google Scholar
Etter, M. C. (1990). Acc. Chem. Res. 23, 120–126. CrossRef CAS Web of Science Google Scholar
Johansen, T. N., Ebert, B., Bräuner-Osborne, H., Didriksen, M., Christensen, I. T., Søby, K. K., Madsen, U., Krogsgaard-Larsen, P. & Brehm, L. (1998). J. Med. Chem. 41, 930–939. Web of Science CSD CrossRef CAS PubMed Google Scholar
Kinbara, K., Hashimoto, Y., Sukegawa, M., Nohira, H. & Saigo, K. (1996). J. Am. Chem. Soc. 118, 3441–3449. CSD CrossRef CAS Web of Science Google Scholar
Kinbara, K., Kai, A., Maekawa, Y., Hashimoto, Y., Naruse, S., Hasegawa, M. & Saigo, K. (1996). J. Chem. Soc. Perkin Trans 2, pp. 247–253. CrossRef Google Scholar
Lemmerer, A., Bourne, S. A. & Fernandes, M. A. (2008). Cryst. Growth Des. 8, 1106–1109. Web of Science CSD CrossRef CAS Google Scholar
Macrae, C. F., Bruno, I. J., Chisholm, J. A., Edgington, P. R., McCabe, P., Pidcock, E., Rodriguez-Monge, L., Taylor, R., van de Streek, J. & Wood, P. A. (2008). J. Appl. Cryst. 41, 466–470. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Siemens (1996). XSCANS. Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA. Google Scholar
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In their works about optical resolution of conglomerates, Kinbara et al. noted that characteristic hydrogen-bond networks were formed in the salt crystals of 1-phenylethylamine and 1-(4-isopropylphenyl)ethylamine with cinnamic acid (Kinbara, Kai et al., 1996). They suggested that "the pattern of hydrogen bonds plays a significant role in the formation of conglomerates" (Kinbara, Hashimoto et al., 1996). In the specific case of salts of chiral 1-phenylethylamine with achiral monocarboxylic acids, a number of structural determinations indeed showed that two predominant supramolecular arrangements are favored by the charge assisted N—H···O hydrogen bonds, which result in crystals belonging to P21 or P212121 space groups (Lemmerer et al., 2008): cations and anions associate through quite strong hydrogen bonds to form C21(4)C22(6)[R43(10)] motifs (Etter, 1990; Bernstein et al., 1995). This basic unit has hydrogen bonds with translational units, forming an infinite columnar structure, which generates a screw axis in the crystal structure (invariably a 21 axis). This supramolecular structure, referred as '21–column' in the Kinbara's reports, may be arranged in a parallel packing in the crystal, which then belongs to P21 space group, or in an antiparallel fashion, generating P212121 crystals.
The chiral title salt (Fig. 1) clearly falls in the latter category. Both the cation and anion are placed in general positions in an orthorhombic unit cell. All ammonium H atoms form hydrogen bonds with carboxylate O atoms, giving a ring motif R43(10), as shown in Fig. 2. The strongest hydrogen bond, N1—H1C···O2ii is common to two rings motifs. The repetition of the motif in the [010] direction generates homochiral (R)–21–columns. This 1D supramolecular network includes larger ring motifs, which appear if shared contacts are omitted. The sequence of sub-rings nest is R43(10) → R65(16) → R87(22) → R109(28) → ··· → R2n2n-1(6n-2) [with n > 1]. The shortest contact between neighboring 21–columns is N1—H1B···F2i, which should be regarded as a van der Waals contact rather than as an actual hydrogen bond. As a consequence, an antiparallel arrangement of 21–columns is favored (Fig. 2, inset), which is, in turn, reflected in the P212121 space group. Such crystal structures were obtained for numerous 1-phenylethylamine salts including different anions, e.g. bromofluoroacetate (Boussac et al., 2002), m-iodobenzoate (Lemmerer et al., 2008) or more complex, bulky carboxylate derivatives (Johansen et al., 1998).
The above description is thus in line with expectations from previous reported structures, and confirms that salts based on chiral 1-phenylethylamine and achiral monocarboxylic acids are robust heterosynthons, useful for crystal engineering and crystal structure prediction. The feature should however not been transferred to other salts (or worse, to cocrystals) of 1-phenylethylamine, which stabilize different supramolecular motifs, if any.