Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536801015240/ci6062sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536801015240/ci6062Isup2.hkl |
CCDC reference: 175370
Key indicators
- Single-crystal X-ray study
- T = 293 K
- Mean (C-C) = 0.003 Å
- R factor = 0.028
- wR factor = 0.078
- Data-to-parameter ratio = 7.2
checkCIF results
No syntax errors found ADDSYM reports no extra symmetry General Notes
REFLT_03 From the CIF: _diffrn_reflns_theta_max 67.92 From the CIF: _reflns_number_total 1353 Count of symmetry unique reflns 1352 Completeness (_total/calc) 100.07% TEST3: Check Friedels for noncentro structure Estimate of Friedel pairs measured 1 Fraction of Friedel pairs measured 0.001 Are heavy atom types Z>Si present no Please check that the estimate of the number of Friedel pairs is correct. If it is not, please give the correct count in the _publ_section_exptl_refinement section of the submitted CIF.
Colorless single crystals of (I) were grown as transparent needles from a saturated aqueous solution containing L-alanine and maleic acid in a 1:1 stoichiometric ratio.
The absolute configuration of L-phenylalaninium maleate was not established by the analysis but is known from the configuration of the starting reagents. The H atoms were placed at calculated positions and were allowed to ride on their respective parent atoms with HFIX instructions using SHELXL97 (Sheldrick, 1997) defaults. The H atom shared between O3 and O5 atoms of the semimaleate anion is, however, refined isotropically.
Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: CAD-4 Software; 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. Packing of the molecules of (I) viewed down the b axis. |
C9H12NO2+·C4H3O4− | F(000) = 296 |
Mr = 281.26 | Dx = 1.407 Mg m−3 Dm = 1.41 Mg m−3 Dm measured by flotation in mixture of xylene and bromoform |
Monoclinic, P21 | Cu Kα radiation, λ = 1.54180 Å |
a = 11.0560 (9) Å | Cell parameters from 25 reflections |
b = 5.3326 (4) Å | θ = 28–42° |
c = 11.4712 (7) Å | µ = 0.96 mm−1 |
β = 101.07 (1)° | T = 293 K |
V = 663.73 (8) Å3 | Needle, colorless |
Z = 2 | 0.40 × 0.10 × 0.10 mm |
Enraf-Nonius CAD-4 diffractometer | 1294 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.015 |
Graphite monochromator | θmax = 67.9°, θmin = 3.9° |
ω–2θ scans | h = −13→0 |
Absorption correction: ψ scan (North et al., 1968) | k = 0→6 |
Tmin = 0.82, Tmax = 0.91 | l = −13→13 |
1424 measured reflections | 2 standard reflections every 100 reflections |
1353 independent reflections | intensity decay: <2% |
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)] = 0.028 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.078 | w = 1/[σ2(Fo2) + (0.0418P)2 + 0.0901P] where P = (Fo2 + 2Fc2)/3 |
S = 1.13 | (Δ/σ)max < 0.001 |
1353 reflections | Δρmax = 0.12 e Å−3 |
187 parameters | Δρmin = −0.12 e Å−3 |
1 restraint | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.052 (3) |
C9H12NO2+·C4H3O4− | V = 663.73 (8) Å3 |
Mr = 281.26 | Z = 2 |
Monoclinic, P21 | Cu Kα radiation |
a = 11.0560 (9) Å | µ = 0.96 mm−1 |
b = 5.3326 (4) Å | T = 293 K |
c = 11.4712 (7) Å | 0.40 × 0.10 × 0.10 mm |
β = 101.07 (1)° |
Enraf-Nonius CAD-4 diffractometer | 1294 reflections with I > 2σ(I) |
Absorption correction: ψ scan (North et al., 1968) | Rint = 0.015 |
Tmin = 0.82, Tmax = 0.91 | 2 standard reflections every 100 reflections |
1424 measured reflections | intensity decay: <2% |
1353 independent reflections |
R[F2 > 2σ(F2)] = 0.028 | 1 restraint |
wR(F2) = 0.078 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.13 | Δρmax = 0.12 e Å−3 |
1353 reflections | Δρmin = −0.12 e Å−3 |
187 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 | 0.21671 (16) | 0.2656 (4) | 0.40613 (13) | 0.0593 (5) | |
H1 | 0.1884 | 0.3756 | 0.3588 | 0.089* | |
O2 | 0.09656 (12) | 0.4396 (3) | 0.51853 (11) | 0.0427 (4) | |
O3 | 0.89837 (18) | 0.3761 (4) | 0.88035 (14) | 0.0600 (5) | |
O4 | 0.86654 (15) | 0.1424 (4) | 0.72068 (13) | 0.0556 (5) | |
O5 | 0.86833 (19) | 0.3497 (4) | 1.08272 (15) | 0.0626 (5) | |
O6 | 0.81953 (17) | 0.0653 (4) | 1.20320 (13) | 0.0623 (5) | |
N1 | 0.12481 (14) | 0.0781 (4) | 0.67720 (15) | 0.0465 (5) | |
H1A | 0.1359 | −0.0571 | 0.7235 | 0.070* | |
H1B | 0.0445 | 0.1081 | 0.6547 | 0.070* | |
H1C | 0.1611 | 0.2095 | 0.7172 | 0.070* | |
C1 | 0.16094 (16) | 0.2707 (4) | 0.49675 (16) | 0.0341 (4) | |
C2 | 0.17990 (17) | 0.0341 (4) | 0.57051 (18) | 0.0379 (5) | |
H2 | 0.1316 | −0.0986 | 0.5240 | 0.045* | |
C3 | 0.31263 (17) | −0.0598 (5) | 0.60380 (19) | 0.0424 (5) | |
H3A | 0.3123 | −0.2202 | 0.6437 | 0.051* | |
H3B | 0.3435 | −0.0884 | 0.5313 | 0.051* | |
C4 | 0.40088 (16) | 0.1127 (4) | 0.68253 (17) | 0.0384 (5) | |
C5 | 0.4201 (2) | 0.0880 (6) | 0.8048 (2) | 0.0537 (6) | |
H5 | 0.3785 | −0.0362 | 0.8383 | 0.064* | |
C6 | 0.5001 (2) | 0.2454 (7) | 0.8774 (2) | 0.0645 (8) | |
H6 | 0.5115 | 0.2274 | 0.9595 | 0.077* | |
C7 | 0.5628 (2) | 0.4274 (7) | 0.8300 (2) | 0.0619 (7) | |
H7 | 0.6170 | 0.5325 | 0.8794 | 0.074* | |
C8 | 0.5454 (2) | 0.4546 (6) | 0.7089 (2) | 0.0621 (7) | |
H8 | 0.5875 | 0.5787 | 0.6760 | 0.074* | |
C9 | 0.4650 (2) | 0.2971 (5) | 0.6359 (2) | 0.0513 (6) | |
H9 | 0.4540 | 0.3159 | 0.5540 | 0.062* | |
C10 | 0.86352 (19) | 0.1716 (4) | 0.82772 (18) | 0.0420 (5) | |
C11 | 0.8215 (2) | −0.0398 (5) | 0.89285 (19) | 0.0470 (5) | |
H11 | 0.7984 | −0.1826 | 0.8474 | 0.056* | |
C12 | 0.8112 (2) | −0.0586 (5) | 1.00627 (19) | 0.0489 (5) | |
H12 | 0.7851 | −0.2146 | 1.0279 | 0.059* | |
C13 | 0.8346 (2) | 0.1277 (5) | 1.10374 (19) | 0.0460 (5) | |
H3 | 0.884 (3) | 0.355 (8) | 0.975 (3) | 0.091 (10)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0771 (11) | 0.0642 (12) | 0.0418 (8) | 0.0283 (10) | 0.0245 (7) | 0.0151 (8) |
O2 | 0.0488 (7) | 0.0392 (9) | 0.0417 (7) | 0.0089 (7) | 0.0129 (6) | 0.0095 (7) |
O3 | 0.0919 (12) | 0.0431 (10) | 0.0479 (9) | −0.0199 (9) | 0.0205 (8) | −0.0143 (8) |
O4 | 0.0729 (10) | 0.0562 (11) | 0.0411 (8) | −0.0106 (9) | 0.0195 (7) | −0.0131 (8) |
O5 | 0.1022 (14) | 0.0415 (10) | 0.0455 (9) | −0.0062 (10) | 0.0175 (8) | −0.0174 (8) |
O6 | 0.0829 (11) | 0.0662 (13) | 0.0419 (8) | 0.0039 (11) | 0.0224 (8) | −0.0079 (9) |
N1 | 0.0374 (8) | 0.0532 (12) | 0.0491 (9) | 0.0006 (9) | 0.0087 (7) | 0.0233 (10) |
C1 | 0.0340 (8) | 0.0335 (10) | 0.0326 (9) | 0.0003 (9) | 0.0011 (7) | 0.0034 (8) |
C2 | 0.0381 (9) | 0.0306 (10) | 0.0416 (10) | −0.0019 (9) | −0.0008 (7) | 0.0051 (9) |
C3 | 0.0431 (10) | 0.0310 (10) | 0.0508 (11) | 0.0058 (9) | 0.0031 (8) | 0.0029 (10) |
C4 | 0.0296 (8) | 0.0379 (11) | 0.0463 (10) | 0.0051 (9) | 0.0040 (7) | 0.0050 (9) |
C5 | 0.0501 (11) | 0.0598 (16) | 0.0488 (12) | −0.0092 (13) | 0.0031 (9) | 0.0130 (12) |
C6 | 0.0602 (14) | 0.083 (2) | 0.0460 (12) | −0.0126 (16) | −0.0003 (10) | 0.0015 (15) |
C7 | 0.0472 (11) | 0.0696 (19) | 0.0659 (15) | −0.0112 (14) | 0.0033 (10) | −0.0129 (15) |
C8 | 0.0525 (12) | 0.0627 (17) | 0.0724 (15) | −0.0194 (14) | 0.0154 (11) | 0.0028 (15) |
C9 | 0.0483 (11) | 0.0581 (16) | 0.0485 (11) | −0.0093 (13) | 0.0116 (9) | 0.0053 (12) |
C10 | 0.0459 (10) | 0.0411 (12) | 0.0400 (10) | −0.0007 (10) | 0.0108 (8) | −0.0112 (10) |
C11 | 0.0616 (12) | 0.0360 (12) | 0.0434 (11) | −0.0081 (11) | 0.0100 (9) | −0.0150 (10) |
C12 | 0.0650 (13) | 0.0383 (12) | 0.0441 (11) | −0.0061 (12) | 0.0121 (9) | −0.0068 (10) |
C13 | 0.0524 (11) | 0.0478 (14) | 0.0390 (11) | 0.0055 (11) | 0.0115 (9) | −0.0096 (10) |
O1—C1 | 1.307 (2) | C3—H3B | 0.97 |
O1—H1 | 0.82 | C4—C9 | 1.379 (3) |
O2—C1 | 1.203 (3) | C4—C5 | 1.384 (3) |
O3—C10 | 1.270 (3) | C5—C6 | 1.378 (4) |
O3—H3 | 1.13 (3) | C5—H5 | 0.93 |
O4—C10 | 1.244 (2) | C6—C7 | 1.366 (4) |
O5—C13 | 1.278 (3) | C6—H6 | 0.93 |
O5—H3 | 1.28 (3) | C7—C8 | 1.373 (4) |
O6—C13 | 1.230 (3) | C7—H7 | 0.93 |
N1—C2 | 1.486 (3) | C8—C9 | 1.381 (4) |
N1—H1A | 0.89 | C8—H8 | 0.93 |
N1—H1B | 0.89 | C9—H9 | 0.93 |
N1—H1C | 0.89 | C10—C11 | 1.476 (3) |
C1—C2 | 1.511 (3) | C11—C12 | 1.331 (3) |
C2—C3 | 1.528 (3) | C11—H11 | 0.93 |
C2—H2 | 0.98 | C12—C13 | 1.481 (3) |
C3—C4 | 1.508 (3) | C12—H12 | 0.93 |
C3—H3A | 0.97 | ||
C1—O1—H1 | 109.5 | C6—C5—C4 | 120.7 (2) |
C10—O3—H3 | 106 (2) | C6—C5—H5 | 119.6 |
C13—O5—H3 | 107 (2) | C4—C5—H5 | 119.6 |
C2—N1—H1A | 109.5 | C7—C6—C5 | 120.5 (2) |
C2—N1—H1B | 109.5 | C7—C6—H6 | 119.7 |
H1A—N1—H1B | 109.5 | C5—C6—H6 | 119.7 |
C2—N1—H1C | 109.5 | C6—C7—C8 | 119.7 (2) |
H1A—N1—H1C | 109.5 | C6—C7—H7 | 120.2 |
H1B—N1—H1C | 109.5 | C8—C7—H7 | 120.2 |
O2—C1—O1 | 124.68 (19) | C7—C8—C9 | 119.8 (2) |
O2—C1—C2 | 122.17 (17) | C7—C8—H8 | 120.1 |
O1—C1—C2 | 113.08 (18) | C9—C8—H8 | 120.1 |
N1—C2—C1 | 107.14 (17) | C4—C9—C8 | 121.2 (2) |
N1—C2—C3 | 111.81 (16) | C4—C9—H9 | 119.4 |
C1—C2—C3 | 115.91 (17) | C8—C9—H9 | 119.4 |
N1—C2—H2 | 107.2 | O4—C10—O3 | 120.9 (2) |
C1—C2—H2 | 107.2 | O4—C10—C11 | 118.3 (2) |
C3—C2—H2 | 107.2 | O3—C10—C11 | 120.76 (18) |
C4—C3—C2 | 115.43 (19) | C12—C11—C10 | 130.3 (2) |
C4—C3—H3A | 108.4 | C12—C11—H11 | 114.9 |
C2—C3—H3A | 108.4 | C10—C11—H11 | 114.9 |
C4—C3—H3B | 108.4 | C11—C12—C13 | 130.7 (2) |
C2—C3—H3B | 108.4 | C11—C12—H12 | 114.6 |
H3A—C3—H3B | 107.5 | C13—C12—H12 | 114.6 |
C9—C4—C5 | 118.1 (2) | O6—C13—O5 | 121.5 (2) |
C9—C4—C3 | 121.64 (19) | O6—C13—C12 | 118.9 (2) |
C5—C4—C3 | 120.3 (2) | O5—C13—C12 | 119.6 (2) |
O2—C1—C2—N1 | −9.4 (2) | C5—C6—C7—C8 | 0.4 (5) |
O1—C1—C2—N1 | 173.33 (17) | C6—C7—C8—C9 | −0.3 (4) |
O2—C1—C2—C3 | −135.0 (2) | C5—C4—C9—C8 | −0.6 (4) |
O1—C1—C2—C3 | 47.7 (2) | C3—C4—C9—C8 | 179.8 (2) |
N1—C2—C3—C4 | −59.3 (2) | C7—C8—C9—C4 | 0.4 (4) |
C1—C2—C3—C4 | 63.9 (2) | O4—C10—C11—C12 | 179.0 (2) |
C2—C3—C4—C9 | −88.8 (2) | O3—C10—C11—C12 | 0.6 (4) |
C2—C3—C4—C5 | 91.5 (3) | C10—C11—C12—C13 | 2.2 (4) |
C9—C4—C5—C6 | 0.7 (4) | C11—C12—C13—O6 | −179.3 (3) |
C3—C4—C5—C6 | −179.7 (2) | C11—C12—C13—O5 | 1.5 (4) |
C4—C5—C6—C7 | −0.6 (4) |
D—H···A | D—H | H···A | D···A | D—H···A |
O3—H3···O5 | 1.13 (3) | 1.28 (3) | 2.412 (2) | 175 (4) |
O1—H1···O4i | 0.82 | 1.73 | 2.547 (2) | 170 |
N1—H1A···O5ii | 0.89 | 2.29 | 2.999 (2) | 137 |
N1—H1A···O6ii | 0.89 | 2.20 | 3.068 (3) | 164 |
N1—H1B···O2iii | 0.89 | 2.45 | 3.077 (2) | 128 |
N1—H1B···O4iv | 0.89 | 2.25 | 3.011 (2) | 144 |
N1—H1C···O6v | 0.89 | 2.10 | 2.947 (3) | 159 |
C2—H2···O2vi | 0.98 | 2.49 | 3.324 (3) | 142 |
C2—H2···O2iii | 0.98 | 2.48 | 3.073 (2) | 118 |
C11—H11···O3vi | 0.93 | 2.60 | 3.239 (3) | 127 |
C12—H12···O5vi | 0.93 | 2.53 | 3.303 (3) | 140 |
Symmetry codes: (i) −x+1, y+1/2, −z+1; (ii) −x+1, y−1/2, −z+2; (iii) −x, y−1/2, −z+1; (iv) x−1, y, z; (v) −x+1, y+1/2, −z+2; (vi) x, y−1, z. |
Experimental details
Crystal data | |
Chemical formula | C9H12NO2+·C4H3O4− |
Mr | 281.26 |
Crystal system, space group | Monoclinic, P21 |
Temperature (K) | 293 |
a, b, c (Å) | 11.0560 (9), 5.3326 (4), 11.4712 (7) |
β (°) | 101.07 (1) |
V (Å3) | 663.73 (8) |
Z | 2 |
Radiation type | Cu Kα |
µ (mm−1) | 0.96 |
Crystal size (mm) | 0.40 × 0.10 × 0.10 |
Data collection | |
Diffractometer | Enraf-Nonius CAD-4 diffractometer |
Absorption correction | ψ scan (North et al., 1968) |
Tmin, Tmax | 0.82, 0.91 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 1424, 1353, 1294 |
Rint | 0.015 |
(sin θ/λ)max (Å−1) | 0.601 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.028, 0.078, 1.13 |
No. of reflections | 1353 |
No. of parameters | 187 |
No. of restraints | 1 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.12, −0.12 |
Computer programs: CAD-4 Software (Enraf-Nonius, 1989), CAD-4 Software, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), PLATON (Spek, 1999), SHELXL97.
O1—C1 | 1.307 (2) | C3—C4 | 1.508 (3) |
O2—C1 | 1.203 (3) | C4—C9 | 1.379 (3) |
O3—C10 | 1.270 (3) | C4—C5 | 1.384 (3) |
O4—C10 | 1.244 (2) | C5—C6 | 1.378 (4) |
O5—C13 | 1.278 (3) | C6—C7 | 1.366 (4) |
O5—H3 | 1.28 (3) | C7—C8 | 1.373 (4) |
O6—C13 | 1.230 (3) | C8—C9 | 1.381 (4) |
N1—C2 | 1.486 (3) | C10—C11 | 1.476 (3) |
C1—C2 | 1.511 (3) | C11—C12 | 1.331 (3) |
C2—C3 | 1.528 (3) | C12—C13 | 1.481 (3) |
O2—C1—O1 | 124.68 (19) | C6—C7—C8 | 119.7 (2) |
O2—C1—C2 | 122.17 (17) | C7—C8—C9 | 119.8 (2) |
O1—C1—C2 | 113.08 (18) | C4—C9—C8 | 121.2 (2) |
N1—C2—C1 | 107.14 (17) | O4—C10—O3 | 120.9 (2) |
N1—C2—C3 | 111.81 (16) | O4—C10—C11 | 118.3 (2) |
C1—C2—C3 | 115.91 (17) | O3—C10—C11 | 120.76 (18) |
C4—C3—C2 | 115.43 (19) | C12—C11—C10 | 130.3 (2) |
C9—C4—C5 | 118.1 (2) | C11—C12—C13 | 130.7 (2) |
C9—C4—C3 | 121.64 (19) | O6—C13—O5 | 121.5 (2) |
C5—C4—C3 | 120.3 (2) | O6—C13—C12 | 118.9 (2) |
C6—C5—C4 | 120.7 (2) | O5—C13—C12 | 119.6 (2) |
C7—C6—C5 | 120.5 (2) | ||
O2—C1—C2—N1 | −9.4 (2) | O1—C1—C2—C3 | 47.7 (2) |
O1—C1—C2—N1 | 173.33 (17) | N1—C2—C3—C4 | −59.3 (2) |
O2—C1—C2—C3 | −135.0 (2) | C1—C2—C3—C4 | 63.9 (2) |
D—H···A | D—H | H···A | D···A | D—H···A |
O3—H3···O5 | 1.13 (3) | 1.28 (3) | 2.412 (2) | 175 (4) |
O1—H1···O4i | 0.82 | 1.73 | 2.547 (2) | 170 |
N1—H1A···O5ii | 0.89 | 2.29 | 2.999 (2) | 137 |
N1—H1A···O6ii | 0.89 | 2.20 | 3.068 (3) | 164 |
N1—H1B···O2iii | 0.89 | 2.45 | 3.077 (2) | 128 |
N1—H1B···O4iv | 0.89 | 2.25 | 3.011 (2) | 144 |
N1—H1C···O6v | 0.89 | 2.10 | 2.947 (3) | 159 |
C2—H2···O2vi | 0.98 | 2.49 | 3.324 (3) | 142 |
C2—H2···O2iii | 0.98 | 2.48 | 3.073 (2) | 118 |
C11—H11···O3vi | 0.93 | 2.60 | 3.239 (3) | 127 |
C12—H12···O5vi | 0.93 | 2.53 | 3.303 (3) | 140 |
Symmetry codes: (i) −x+1, y+1/2, −z+1; (ii) −x+1, y−1/2, −z+2; (iii) −x, y−1/2, −z+1; (iv) x−1, y, z; (v) −x+1, y+1/2, −z+2; (vi) x, y−1, z. |
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Phenylalanine, an essential amino acid commonly found in proteins, plays a key role in the formation of a variety of physiologically important chemicals that transmit signals between nerve cells. Previous works on phenylalanine report only the unit-cell dimensions (Khawas & Murthi, 1968; Khawas, 1970, 1971, 1985) and the crystal structure of the D-form with a high agreement factor of 15% (Weissbuch et al., 1990). The crystal structure of L-phenylalanine, however, is yet to be reported. A number of complexes of L-phenylalanine with inorganic acids are already known. The present study, which reports the crystal structure of L-phenylalaninium maleate, (I), is part of a series of X-ray investigations being carried out in our laboratory on amino acid–carboxylic acid complexes. Recently, the crystal structure of glycinium maleate (Rajagopal, Krishnakumar, Mostad & Natarajan, 2001), L-alaninium maleate (Alagar et al., 2001) and β-alaninium maleate (Rajagopal, Krishnakumar & Natarajan, 2001) have been reported.
Fig. 1 shows the molecular structure of (I) with the atom-numbering scheme adopted. The amino acid molecule exists in the cationic form with a positively charged amino group and an uncharged carboxylic acid group. The phenylalaninium cation has the gauche- conformation with a χ1 value of -59.3 (2)°. This is different from the values observed in L-phenylalanine L-phenylalaninium formate with χ1 = 72.3 (4) and 70.8 (4)°, respectively, for the zwitterion and the cation (Gorbitz & Etter, 1992). The maleic acid molecule exists in the mono-ionized state (i.e. as a semi-maleate anion). In the semi-maleate anion, a nearly symmetric intramolecular hydrogen bond with a proton shared between the O3 and O5 atoms is observed as in the crystal structures of complexes of maleic acid with DL– and L-arginine (Ravishankar et al., 1998) and L-histidine and L-lysine (Pratap et al., 2000). However, in the crystal structures of maleic acid itself (James & Williams, 1974), glycinium maleate and L-alaninium maleate, this intramolecular hydrogen bond is asymmetric.
Fig. 2 shows the packing of the molecules of (I) viewed down the b axis. The phenylalaninium cations and the semimaleate anions form hydrogen-bonded double chains in which they alternate along the c axis and are held together by N—H···O hydrogen bonds. The double chain, on either side, is flanked by the hydrophobic side chains of phenylalanine leading to alternating hydrophilic and hydrophobic zones along the a axis. These double chains form an infinite two-dimensional network extending along the b axis, interconnected through O—H···O, N—H···O and C—H···O hydrogen bonds. The aggregation pattern observed in (I) has striking similarities with those observed in L-phenylalanine L-phenylalaninium formate (Gorbitz & Etter, 1992) and L-phenylalanine L-phenylalaninium perchlorate (Srinivasan & Rajaram, 1997).