Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S160053680202295X/ci6190sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S160053680202295X/ci6190Isup2.hkl |
CCDC reference: 204707
Colourless single crystals of (I) were grown as transparent plates from a saturated aqueous solution containing DL-phenylalanine and maleic acid in a 1:1 stoichiometric ratio.
After checking their presence in the difference map, all H atoms were positioned geometrically and were allowed to ride on their respective parent atoms with SHELXL97 (Sheldrick, 1997) defaults for bond lengths and isotropic displacement parameters. Rotating-group refinement was used for the OH groups.
Data collection: SMART (Bruker, 1999); cell refinement: SMART; data reduction: SAINT (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1999); software used to prepare material for publication: SHELXL97.
Fig. 1. The molecular structure of (I) with the atom-numbering scheme and 50% probability displacement ellipsoids. | |
Fig. 2. The packing of the molecules of (I), viewed down the b axis. |
C9H12NO2+·C4H3O4− | F(000) = 592 |
Mr = 281.26 | Dx = 1.420 Mg m−3 Dm = 1.42 Mg m−3 Dm measured by flotation in mixture of xylene and bromoform |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2yn | Cell parameters from 1024 reflections |
a = 12.308 (3) Å | θ = 1.9–26.4° |
b = 5.9942 (12) Å | µ = 0.11 mm−1 |
c = 18.061 (4) Å | T = 123 K |
β = 99.15 (3)° | Plate, colourless |
V = 1315.5 (5) Å3 | 0.3 × 0.3 × 0.1 mm |
Z = 4 |
Bruker SMART CCD diffractometer | 2704 independent reflections |
Radiation source: fine-focus sealed tube | 2250 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.043 |
Detector resolution: 8 pixels mm-1 | θmax = 26.4°, θmin = 1.9° |
ω scans | h = −15→15 |
Absorption correction: multi-scan (SADABS; Bruker, 1998) | k = −7→7 |
Tmin = 0.97, Tmax = 0.99 | l = −22→22 |
13028 measured reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.045 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.146 | H-atom parameters constrained |
S = 1.13 | w = 1/[σ2(Fo2) + (0.077P)2 + 0.6066P] where P = (Fo2 + 2Fc2)/3 |
2704 reflections | (Δ/σ)max < 0.001 |
183 parameters | Δρmax = 0.34 e Å−3 |
0 restraints | Δρmin = −0.34 e Å−3 |
C9H12NO2+·C4H3O4− | V = 1315.5 (5) Å3 |
Mr = 281.26 | Z = 4 |
Monoclinic, P21/n | Mo Kα radiation |
a = 12.308 (3) Å | µ = 0.11 mm−1 |
b = 5.9942 (12) Å | T = 123 K |
c = 18.061 (4) Å | 0.3 × 0.3 × 0.1 mm |
β = 99.15 (3)° |
Bruker SMART CCD diffractometer | 2704 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 1998) | 2250 reflections with I > 2σ(I) |
Tmin = 0.97, Tmax = 0.99 | Rint = 0.043 |
13028 measured reflections |
R[F2 > 2σ(F2)] = 0.045 | 0 restraints |
wR(F2) = 0.146 | H-atom parameters constrained |
S = 1.13 | Δρmax = 0.34 e Å−3 |
2704 reflections | Δρmin = −0.34 e Å−3 |
183 parameters |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.13825 (13) | 1.3674 (2) | −0.15043 (8) | 0.0355 (4) | |
H1 | 0.1101 | 1.4338 | −0.1884 | 0.053* | |
O2 | 0.20333 (13) | 1.1386 (2) | −0.23179 (7) | 0.0328 (3) | |
O3 | 0.92375 (12) | 0.6878 (2) | 0.52559 (7) | 0.0314 (3) | |
H3 | 0.9543 | 0.6382 | 0.5659 | 0.047* | |
O4 | 0.84354 (12) | 0.9987 (2) | 0.48147 (7) | 0.0305 (3) | |
O5 | 1.05343 (13) | 0.6794 (2) | 0.76513 (8) | 0.0367 (4) | |
O6 | 1.02083 (12) | 0.5538 (2) | 0.64761 (8) | 0.0321 (3) | |
N1 | 0.28096 (13) | 0.8413 (2) | −0.12824 (8) | 0.0236 (3) | |
H1A | 0.3018 | 0.7490 | −0.0900 | 0.035* | |
H1B | 0.3401 | 0.8908 | −0.1458 | 0.035* | |
H1C | 0.2372 | 0.7691 | −0.1644 | 0.035* | |
C1 | 0.18664 (15) | 1.1856 (3) | −0.16946 (10) | 0.0242 (4) | |
C2 | 0.22052 (15) | 1.0331 (3) | −0.10227 (9) | 0.0230 (4) | |
H2A | 0.2699 | 1.1148 | −0.0637 | 0.028* | |
C3 | 0.11943 (15) | 0.9547 (3) | −0.06942 (10) | 0.0284 (4) | |
H3A | 0.0650 | 1.0730 | −0.0759 | 0.034* | |
H3B | 0.0877 | 0.8271 | −0.0981 | 0.034* | |
C4 | 0.14166 (15) | 0.8906 (3) | 0.01264 (10) | 0.0262 (4) | |
C5 | 0.11659 (18) | 0.6797 (4) | 0.03554 (13) | 0.0379 (5) | |
H5 | 0.0926 | 0.5712 | −0.0002 | 0.046* | |
C6 | 0.1269 (2) | 0.6273 (5) | 0.11139 (16) | 0.0596 (8) | |
H6 | 0.1083 | 0.4858 | 0.1264 | 0.071* | |
C7 | 0.1652 (3) | 0.7884 (7) | 0.16457 (14) | 0.0691 (10) | |
H7 | 0.1724 | 0.7553 | 0.2154 | 0.083* | |
C8 | 0.1924 (2) | 0.9973 (6) | 0.14149 (14) | 0.0628 (8) | |
H8 | 0.2186 | 1.1048 | 0.1770 | 0.075* | |
C9 | 0.18106 (19) | 1.0483 (4) | 0.06614 (12) | 0.0414 (5) | |
H9 | 0.2000 | 1.1896 | 0.0512 | 0.050* | |
C10 | 0.89634 (14) | 0.8952 (3) | 0.53398 (10) | 0.0245 (4) | |
C11 | 0.92789 (16) | 1.0109 (3) | 0.60772 (10) | 0.0273 (4) | |
H11 | 0.9105 | 1.1619 | 0.6072 | 0.033* | |
C12 | 0.97666 (16) | 0.9341 (3) | 0.67400 (10) | 0.0278 (4) | |
H12 | 0.9858 | 1.0394 | 0.7123 | 0.033* | |
C13 | 1.01929 (15) | 0.7058 (3) | 0.69695 (10) | 0.0264 (4) |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0497 (9) | 0.0277 (7) | 0.0281 (7) | 0.0135 (6) | 0.0031 (6) | 0.0031 (6) |
O2 | 0.0488 (9) | 0.0275 (7) | 0.0229 (7) | 0.0027 (6) | 0.0084 (6) | 0.0046 (5) |
O3 | 0.0379 (8) | 0.0245 (7) | 0.0286 (7) | 0.0061 (5) | −0.0042 (6) | −0.0052 (5) |
O4 | 0.0369 (8) | 0.0255 (7) | 0.0270 (7) | 0.0001 (6) | −0.0011 (5) | 0.0012 (5) |
O5 | 0.0529 (9) | 0.0288 (7) | 0.0270 (7) | 0.0113 (6) | 0.0019 (6) | 0.0024 (6) |
O6 | 0.0386 (8) | 0.0221 (7) | 0.0336 (7) | 0.0082 (6) | 0.0001 (6) | −0.0047 (5) |
N1 | 0.0310 (8) | 0.0196 (7) | 0.0199 (7) | 0.0002 (6) | 0.0037 (6) | 0.0010 (6) |
C1 | 0.0284 (9) | 0.0202 (8) | 0.0229 (8) | −0.0028 (7) | 0.0008 (7) | 0.0014 (7) |
C2 | 0.0284 (9) | 0.0208 (8) | 0.0191 (8) | 0.0003 (7) | 0.0019 (6) | −0.0007 (6) |
C3 | 0.0269 (9) | 0.0346 (10) | 0.0235 (9) | −0.0006 (8) | 0.0030 (7) | 0.0010 (7) |
C4 | 0.0253 (8) | 0.0294 (9) | 0.0250 (9) | 0.0045 (7) | 0.0070 (7) | 0.0028 (7) |
C5 | 0.0390 (12) | 0.0328 (11) | 0.0459 (12) | 0.0072 (9) | 0.0189 (9) | 0.0071 (9) |
C6 | 0.0616 (17) | 0.0622 (17) | 0.0637 (17) | 0.0315 (14) | 0.0369 (14) | 0.0406 (15) |
C7 | 0.0633 (17) | 0.117 (3) | 0.0293 (12) | 0.0451 (18) | 0.0145 (11) | 0.0309 (15) |
C8 | 0.0573 (16) | 0.100 (2) | 0.0278 (12) | 0.0091 (16) | −0.0021 (10) | −0.0112 (14) |
C9 | 0.0442 (12) | 0.0485 (13) | 0.0314 (11) | −0.0014 (10) | 0.0060 (9) | −0.0052 (9) |
C10 | 0.0240 (8) | 0.0227 (9) | 0.0267 (9) | −0.0028 (7) | 0.0035 (7) | −0.0011 (7) |
C11 | 0.0318 (10) | 0.0183 (8) | 0.0305 (9) | 0.0015 (7) | 0.0006 (7) | −0.0027 (7) |
C12 | 0.0332 (10) | 0.0217 (9) | 0.0276 (9) | 0.0019 (7) | 0.0020 (7) | −0.0059 (7) |
C13 | 0.0287 (9) | 0.0228 (9) | 0.0277 (9) | 0.0028 (7) | 0.0043 (7) | −0.0003 (7) |
O1—C1 | 1.313 (2) | C3—H3B | 0.97 |
O1—H1 | 0.82 | C4—C5 | 1.381 (3) |
O2—C1 | 1.209 (2) | C4—C9 | 1.383 (3) |
O3—C10 | 1.303 (2) | C5—C6 | 1.391 (3) |
O3—H3 | 0.82 | C5—H5 | 0.93 |
O4—C10 | 1.229 (2) | C6—C7 | 1.390 (5) |
O5—C13 | 1.246 (2) | C6—H6 | 0.93 |
O6—C13 | 1.276 (2) | C7—C8 | 1.378 (5) |
N1—C2 | 1.485 (2) | C7—H7 | 0.93 |
N1—H1A | 0.89 | C8—C9 | 1.380 (3) |
N1—H1B | 0.89 | C8—H8 | 0.93 |
N1—H1C | 0.89 | C9—H9 | 0.93 |
C1—C2 | 1.524 (2) | C10—C11 | 1.497 (2) |
C2—C3 | 1.535 (3) | C11—C12 | 1.333 (3) |
C2—H2A | 0.98 | C11—H11 | 0.93 |
C3—C4 | 1.513 (2) | C12—C13 | 1.501 (3) |
C3—H3A | 0.97 | C12—H12 | 0.93 |
C1—O1—H1 | 109.5 | C4—C5—H5 | 119.6 |
C10—O3—H3 | 109.5 | C6—C5—H5 | 119.6 |
C2—N1—H1A | 109.5 | C7—C6—C5 | 119.4 (3) |
C2—N1—H1B | 109.5 | C7—C6—H6 | 120.3 |
H1A—N1—H1B | 109.5 | C5—C6—H6 | 120.3 |
C2—N1—H1C | 109.5 | C8—C7—C6 | 119.6 (2) |
H1A—N1—H1C | 109.5 | C8—C7—H7 | 120.2 |
H1B—N1—H1C | 109.5 | C6—C7—H7 | 120.2 |
O2—C1—O1 | 126.02 (17) | C7—C8—C9 | 120.5 (3) |
O2—C1—C2 | 122.41 (16) | C7—C8—H8 | 119.7 |
O1—C1—C2 | 111.57 (15) | C9—C8—H8 | 119.7 |
N1—C2—C1 | 107.48 (14) | C8—C9—C4 | 120.5 (3) |
N1—C2—C3 | 111.26 (15) | C8—C9—H9 | 119.8 |
C1—C2—C3 | 110.82 (15) | C4—C9—H9 | 119.8 |
N1—C2—H2A | 109.1 | O4—C10—O3 | 120.46 (16) |
C1—C2—H2A | 109.1 | O4—C10—C11 | 118.87 (16) |
C3—C2—H2A | 109.1 | O3—C10—C11 | 120.67 (16) |
C4—C3—C2 | 115.14 (15) | C12—C11—C10 | 130.92 (17) |
C4—C3—H3A | 108.5 | C12—C11—H11 | 114.5 |
C2—C3—H3A | 108.5 | C10—C11—H11 | 114.5 |
C4—C3—H3B | 108.5 | C11—C12—C13 | 130.59 (17) |
C2—C3—H3B | 108.5 | C11—C12—H12 | 114.7 |
H3A—C3—H3B | 107.5 | C13—C12—H12 | 114.7 |
C5—C4—C9 | 119.13 (19) | O5—C13—O6 | 124.02 (17) |
C5—C4—C3 | 120.77 (18) | O5—C13—C12 | 115.88 (16) |
C9—C4—C3 | 119.97 (18) | O6—C13—C12 | 120.09 (16) |
C4—C5—C6 | 120.8 (2) | ||
O2—C1—C2—N1 | 4.1 (2) | C5—C6—C7—C8 | 0.0 (4) |
O1—C1—C2—N1 | −176.15 (15) | C6—C7—C8—C9 | 0.6 (4) |
O2—C1—C2—C3 | −117.6 (2) | C7—C8—C9—C4 | 0.3 (4) |
O1—C1—C2—C3 | 62.1 (2) | C5—C4—C9—C8 | −1.7 (3) |
N1—C2—C3—C4 | 85.72 (19) | C3—C4—C9—C8 | 174.2 (2) |
C1—C2—C3—C4 | −154.75 (16) | O4—C10—C11—C12 | 174.2 (2) |
C2—C3—C4—C5 | −122.01 (19) | O3—C10—C11—C12 | −5.4 (3) |
C2—C3—C4—C9 | 62.1 (2) | C10—C11—C12—C13 | 1.7 (4) |
C9—C4—C5—C6 | 2.3 (3) | C11—C12—C13—O5 | −174.5 (2) |
C3—C4—C5—C6 | −173.65 (19) | C11—C12—C13—O6 | 6.7 (3) |
C4—C5—C6—C7 | −1.4 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H1···O5i | 0.82 | 1.78 | 2.5314 (19) | 151 |
O3—H3···O6 | 0.82 | 1.65 | 2.468 (2) | 176 |
N1—H1A···O4ii | 0.89 | 1.98 | 2.861 (2) | 170 |
N1—H1A···O3ii | 0.89 | 2.40 | 3.047 (2) | 130 |
N1—H1B···O6iii | 0.89 | 1.98 | 2.823 (2) | 159 |
N1—H1C···O2iv | 0.89 | 2.26 | 2.839 (2) | 123 |
N1—H1C···O5v | 0.89 | 2.47 | 3.283 (2) | 152 |
Symmetry codes: (i) x−1, y+1, z−1; (ii) x−1/2, −y+3/2, z−1/2; (iii) −x+3/2, y+1/2, −z+1/2; (iv) −x+1/2, y−1/2, −z−1/2; (v) x−1, y, z−1. |
Experimental details
Crystal data | |
Chemical formula | C9H12NO2+·C4H3O4− |
Mr | 281.26 |
Crystal system, space group | Monoclinic, P21/n |
Temperature (K) | 123 |
a, b, c (Å) | 12.308 (3), 5.9942 (12), 18.061 (4) |
β (°) | 99.15 (3) |
V (Å3) | 1315.5 (5) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.11 |
Crystal size (mm) | 0.3 × 0.3 × 0.1 |
Data collection | |
Diffractometer | Bruker SMART CCD diffractometer |
Absorption correction | Multi-scan (SADABS; Bruker, 1998) |
Tmin, Tmax | 0.97, 0.99 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 13028, 2704, 2250 |
Rint | 0.043 |
(sin θ/λ)max (Å−1) | 0.626 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.045, 0.146, 1.13 |
No. of reflections | 2704 |
No. of parameters | 183 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.34, −0.34 |
Computer programs: SMART (Bruker, 1999), SMART, SAINT (Bruker, 1999), SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), PLATON (Spek, 1999), SHELXL97.
O1—C1 | 1.313 (2) | C4—C5 | 1.381 (3) |
O2—C1 | 1.209 (2) | C4—C9 | 1.383 (3) |
O3—C10 | 1.303 (2) | C5—C6 | 1.391 (3) |
O4—C10 | 1.229 (2) | C6—C7 | 1.390 (5) |
O5—C13 | 1.246 (2) | C7—C8 | 1.378 (5) |
O6—C13 | 1.276 (2) | C8—C9 | 1.380 (3) |
N1—C2 | 1.485 (2) | C10—C11 | 1.497 (2) |
C1—C2 | 1.524 (2) | C11—C12 | 1.333 (3) |
C2—C3 | 1.535 (3) | C12—C13 | 1.501 (3) |
C3—C4 | 1.513 (2) | ||
O2—C1—O1 | 126.02 (17) | C8—C7—C6 | 119.6 (2) |
O2—C1—C2 | 122.41 (16) | C7—C8—C9 | 120.5 (3) |
O1—C1—C2 | 111.57 (15) | C8—C9—C4 | 120.5 (3) |
N1—C2—C1 | 107.48 (14) | O4—C10—O3 | 120.46 (16) |
N1—C2—C3 | 111.26 (15) | O4—C10—C11 | 118.87 (16) |
C1—C2—C3 | 110.82 (15) | O3—C10—C11 | 120.67 (16) |
C4—C3—C2 | 115.14 (15) | C12—C11—C10 | 130.92 (17) |
C5—C4—C9 | 119.13 (19) | C11—C12—C13 | 130.59 (17) |
C5—C4—C3 | 120.77 (18) | O5—C13—O6 | 124.02 (17) |
C9—C4—C3 | 119.97 (18) | O5—C13—C12 | 115.88 (16) |
C4—C5—C6 | 120.8 (2) | O6—C13—C12 | 120.09 (16) |
C7—C6—C5 | 119.4 (3) | ||
O2—C1—C2—N1 | 4.1 (2) | C5—C6—C7—C8 | 0.0 (4) |
O1—C1—C2—N1 | −176.15 (15) | C6—C7—C8—C9 | 0.6 (4) |
O2—C1—C2—C3 | −117.6 (2) | C7—C8—C9—C4 | 0.3 (4) |
O1—C1—C2—C3 | 62.1 (2) | C5—C4—C9—C8 | −1.7 (3) |
N1—C2—C3—C4 | 85.72 (19) | C3—C4—C9—C8 | 174.2 (2) |
C1—C2—C3—C4 | −154.75 (16) | O4—C10—C11—C12 | 174.2 (2) |
C2—C3—C4—C5 | −122.01 (19) | O3—C10—C11—C12 | −5.4 (3) |
C2—C3—C4—C9 | 62.1 (2) | C10—C11—C12—C13 | 1.7 (4) |
C9—C4—C5—C6 | 2.3 (3) | C11—C12—C13—O5 | −174.5 (2) |
C3—C4—C5—C6 | −173.65 (19) | C11—C12—C13—O6 | 6.7 (3) |
C4—C5—C6—C7 | −1.4 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H1···O5i | 0.82 | 1.78 | 2.5314 (19) | 151 |
O3—H3···O6 | 0.82 | 1.65 | 2.468 (2) | 176 |
N1—H1A···O4ii | 0.89 | 1.98 | 2.861 (2) | 170 |
N1—H1A···O3ii | 0.89 | 2.40 | 3.047 (2) | 130 |
N1—H1B···O6iii | 0.89 | 1.98 | 2.823 (2) | 159 |
N1—H1C···O2iv | 0.89 | 2.26 | 2.839 (2) | 123 |
N1—H1C···O5v | 0.89 | 2.47 | 3.283 (2) | 152 |
Symmetry codes: (i) x−1, y+1, z−1; (ii) x−1/2, −y+3/2, z−1/2; (iii) −x+3/2, y+1/2, −z+1/2; (iv) −x+1/2, y−1/2, −z−1/2; (v) x−1, y, z−1. |
Phenylalanine, an essential amino acid commonly found in proteins, has a variety of important physiological roles to play in animals. Interestingly, the crystal structure of the L– and racemic forms of phenylalanine remains unknown. However, the crystal structure of its D-form has been reported with a high R factor of 15% (Weissebuch et al., 1990). Though phenylalanine is known to form innumerable complexes with inorganic acids, crystallographic data on the nature of their complexation with organic acids remain scarce. The present study, which reports the crystal structure of DL-phenylalaninium maleate, is part of a series of X-ray investigations being carried out in our laboratory on amino acid–carboxylic acid complexes. Recently, the crystal structures of glycinium maleate (Rajagopal, Krishnakumar, Mostad & Natarajan, 2001), L-alaninium maleate (Alagar, Subha Nandhini, Krishnakumar & Natarajan, 2001), β-alaninium maleate (Rajagopal, Krishnakumar & Natarajan, 2001), DL-valinium maleate (Alagar, Krishnakumar, Mostad & Natarajan, 2001), L-phenylalaninium maleate (Alagar, Krishnakumar & Natarajan, 2001), sarcosinium maleate (Rajagopal et al., 2002) and DL-methioninium maleate (Alagar et al., 2002) have been reported from our laboratory.
Fig. 1 shows the molecular structure of the title compound, (I), with the atom-numbering scheme. The amino acid molecule exists in the cationic form with a positively charged amino group and an uncharged carboxylic acid group. The conformation of the phenylalaninium cation in the present structure considerably differs from that observed in L-phenylalaninium maleate. The torsion angles χ21 and χ22 [−122.0 (2) and 62.1 (2)°, respectively] indicate a distorted folded conformation in the present case. These values are significantly different from those observed in L-phenylalaninium maleate [91.5 (3) and −88.8 (2)°, respectively]. The maleic acid molecule exists in the mono-ionized state (i.e. as a semi-maleate anion). In the semi-maleate anion, the intramolecular hydrogen bond is asymmetric as observed in the crystal structures of maleic acid itself (James & Williams, 1974), glycinium maleate, L-alaninium maleate, DL-valinium maleate and DL-methioninium maleate. However, in the crystal structures of maleic acid with DL– and L-arginine (Ravishankar et al., 1998), L-histidine and L-lysine (Pratap et al., 2000) and L-phenylalaninium maleate, this intramolecular hydrogen bond is symmetric.
Fig. 2 shows the packing of the molecules of (I), viewed down the b axis. The phenylalaninium cations and the semi-maleate anions form hydrogen-bonded double layers linked toegether by N—H···O and O—H···O hydrogen bonds and extend along [101]. These double layers, on either side, are flanked by the hydrophobic side chains of phenylalanine, leading to alternating hydrophilic and hyrophobic zones and have no classic hydrogen-bonded interactions between them. A weak head-to-tail hydrogen bond between the glide-related phenylalaninium ions is present. The aggregation pattern observed in (I) has striking similarities with those observed in L-phenylalanine L-phenylalaninium formate (Görbitz & Etter, 1992), L-phenylalanine L-phenylalaninium perchlorate (Srinivasan & Rajaram, 1997), L-phenylalaninium maleate and other amino acid–maleic acid complexes, viz. glycinium maleate, sarcosinium maleate and DL-valinium maleate. Thus, it seems the mode of assembly of molecules is determined chiefly by semi-maleate anions irrespective of the chemical nature of the amino acids.