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In the title compound, C9H12NO2+·C4H3O4, the amino acid mol­ecule exists in the cationic form with a positively charged amino group and an uncharged carboxyl­ic acid group. The maleic acid mol­ecules exits in the mono-ionized state. In the semi-maleate anion, the intramolecular O—H...O hydrogen bond is asymmetric. The phenyl­alaninium cations and the semi-maleate anions form hydrogen-bonded double layers, linked together by N—H...O and O—H...O hydrogen bonds, extending along [101].

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S160053680202295X/ci6190sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S160053680202295X/ci6190Isup2.hkl
Contains datablock I

CCDC reference: 204707

Key indicators

  • Single-crystal X-ray study
  • T = 123 K
  • Mean [sigma](C-C) = 0.003 Å
  • R factor = 0.045
  • wR factor = 0.146
  • Data-to-parameter ratio = 14.8

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

Comment top

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.

Experimental top

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.

Refinement top

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.

Computing details top

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.

Figures top
[Figure 1] Fig. 1. The molecular structure of (I) with the atom-numbering scheme and 50% probability displacement ellipsoids.
[Figure 2] Fig. 2. The packing of the molecules of (I), viewed down the b axis.
(I) top
Crystal data top
C9H12NO2+·C4H3O4F(000) = 592
Mr = 281.26Dx = 1.420 Mg m3
Dm = 1.42 Mg m3
Dm measured by flotation in mixture of xylene and bromoform
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ynCell parameters from 1024 reflections
a = 12.308 (3) Åθ = 1.9–26.4°
b = 5.9942 (12) ŵ = 0.11 mm1
c = 18.061 (4) ÅT = 123 K
β = 99.15 (3)°Plate, colourless
V = 1315.5 (5) Å30.3 × 0.3 × 0.1 mm
Z = 4
Data collection top
Bruker SMART CCD
diffractometer
2704 independent reflections
Radiation source: fine-focus sealed tube2250 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.043
Detector resolution: 8 pixels mm-1θmax = 26.4°, θmin = 1.9°
ω scansh = 1515
Absorption correction: multi-scan
(SADABS; Bruker, 1998)
k = 77
Tmin = 0.97, Tmax = 0.99l = 2222
13028 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.045Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.146H-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 parametersΔρmax = 0.34 e Å3
0 restraintsΔρmin = 0.34 e Å3
Crystal data top
C9H12NO2+·C4H3O4V = 1315.5 (5) Å3
Mr = 281.26Z = 4
Monoclinic, P21/nMo Kα radiation
a = 12.308 (3) ŵ = 0.11 mm1
b = 5.9942 (12) ÅT = 123 K
c = 18.061 (4) Å0.3 × 0.3 × 0.1 mm
β = 99.15 (3)°
Data collection top
Bruker SMART CCD
diffractometer
2704 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 1998)
2250 reflections with I > 2σ(I)
Tmin = 0.97, Tmax = 0.99Rint = 0.043
13028 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0450 restraints
wR(F2) = 0.146H-atom parameters constrained
S = 1.13Δρmax = 0.34 e Å3
2704 reflectionsΔρmin = 0.34 e Å3
183 parameters
Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O10.13825 (13)1.3674 (2)0.15043 (8)0.0355 (4)
H10.11011.43380.18840.053*
O20.20333 (13)1.1386 (2)0.23179 (7)0.0328 (3)
O30.92375 (12)0.6878 (2)0.52559 (7)0.0314 (3)
H30.95430.63820.56590.047*
O40.84354 (12)0.9987 (2)0.48147 (7)0.0305 (3)
O51.05343 (13)0.6794 (2)0.76513 (8)0.0367 (4)
O61.02083 (12)0.5538 (2)0.64761 (8)0.0321 (3)
N10.28096 (13)0.8413 (2)0.12824 (8)0.0236 (3)
H1A0.30180.74900.09000.035*
H1B0.34010.89080.14580.035*
H1C0.23720.76910.16440.035*
C10.18664 (15)1.1856 (3)0.16946 (10)0.0242 (4)
C20.22052 (15)1.0331 (3)0.10227 (9)0.0230 (4)
H2A0.26991.11480.06370.028*
C30.11943 (15)0.9547 (3)0.06942 (10)0.0284 (4)
H3A0.06501.07300.07590.034*
H3B0.08770.82710.09810.034*
C40.14166 (15)0.8906 (3)0.01264 (10)0.0262 (4)
C50.11659 (18)0.6797 (4)0.03554 (13)0.0379 (5)
H50.09260.57120.00020.046*
C60.1269 (2)0.6273 (5)0.11139 (16)0.0596 (8)
H60.10830.48580.12640.071*
C70.1652 (3)0.7884 (7)0.16457 (14)0.0691 (10)
H70.17240.75530.21540.083*
C80.1924 (2)0.9973 (6)0.14149 (14)0.0628 (8)
H80.21861.10480.17700.075*
C90.18106 (19)1.0483 (4)0.06614 (12)0.0414 (5)
H90.20001.18960.05120.050*
C100.89634 (14)0.8952 (3)0.53398 (10)0.0245 (4)
C110.92789 (16)1.0109 (3)0.60772 (10)0.0273 (4)
H110.91051.16190.60720.033*
C120.97666 (16)0.9341 (3)0.67400 (10)0.0278 (4)
H120.98581.03940.71230.033*
C131.01929 (15)0.7058 (3)0.69695 (10)0.0264 (4)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0497 (9)0.0277 (7)0.0281 (7)0.0135 (6)0.0031 (6)0.0031 (6)
O20.0488 (9)0.0275 (7)0.0229 (7)0.0027 (6)0.0084 (6)0.0046 (5)
O30.0379 (8)0.0245 (7)0.0286 (7)0.0061 (5)0.0042 (6)0.0052 (5)
O40.0369 (8)0.0255 (7)0.0270 (7)0.0001 (6)0.0011 (5)0.0012 (5)
O50.0529 (9)0.0288 (7)0.0270 (7)0.0113 (6)0.0019 (6)0.0024 (6)
O60.0386 (8)0.0221 (7)0.0336 (7)0.0082 (6)0.0001 (6)0.0047 (5)
N10.0310 (8)0.0196 (7)0.0199 (7)0.0002 (6)0.0037 (6)0.0010 (6)
C10.0284 (9)0.0202 (8)0.0229 (8)0.0028 (7)0.0008 (7)0.0014 (7)
C20.0284 (9)0.0208 (8)0.0191 (8)0.0003 (7)0.0019 (6)0.0007 (6)
C30.0269 (9)0.0346 (10)0.0235 (9)0.0006 (8)0.0030 (7)0.0010 (7)
C40.0253 (8)0.0294 (9)0.0250 (9)0.0045 (7)0.0070 (7)0.0028 (7)
C50.0390 (12)0.0328 (11)0.0459 (12)0.0072 (9)0.0189 (9)0.0071 (9)
C60.0616 (17)0.0622 (17)0.0637 (17)0.0315 (14)0.0369 (14)0.0406 (15)
C70.0633 (17)0.117 (3)0.0293 (12)0.0451 (18)0.0145 (11)0.0309 (15)
C80.0573 (16)0.100 (2)0.0278 (12)0.0091 (16)0.0021 (10)0.0112 (14)
C90.0442 (12)0.0485 (13)0.0314 (11)0.0014 (10)0.0060 (9)0.0052 (9)
C100.0240 (8)0.0227 (9)0.0267 (9)0.0028 (7)0.0035 (7)0.0011 (7)
C110.0318 (10)0.0183 (8)0.0305 (9)0.0015 (7)0.0006 (7)0.0027 (7)
C120.0332 (10)0.0217 (9)0.0276 (9)0.0019 (7)0.0020 (7)0.0059 (7)
C130.0287 (9)0.0228 (9)0.0277 (9)0.0028 (7)0.0043 (7)0.0003 (7)
Geometric parameters (Å, º) top
O1—C11.313 (2)C3—H3B0.97
O1—H10.82C4—C51.381 (3)
O2—C11.209 (2)C4—C91.383 (3)
O3—C101.303 (2)C5—C61.391 (3)
O3—H30.82C5—H50.93
O4—C101.229 (2)C6—C71.390 (5)
O5—C131.246 (2)C6—H60.93
O6—C131.276 (2)C7—C81.378 (5)
N1—C21.485 (2)C7—H70.93
N1—H1A0.89C8—C91.380 (3)
N1—H1B0.89C8—H80.93
N1—H1C0.89C9—H90.93
C1—C21.524 (2)C10—C111.497 (2)
C2—C31.535 (3)C11—C121.333 (3)
C2—H2A0.98C11—H110.93
C3—C41.513 (2)C12—C131.501 (3)
C3—H3A0.97C12—H120.93
C1—O1—H1109.5C4—C5—H5119.6
C10—O3—H3109.5C6—C5—H5119.6
C2—N1—H1A109.5C7—C6—C5119.4 (3)
C2—N1—H1B109.5C7—C6—H6120.3
H1A—N1—H1B109.5C5—C6—H6120.3
C2—N1—H1C109.5C8—C7—C6119.6 (2)
H1A—N1—H1C109.5C8—C7—H7120.2
H1B—N1—H1C109.5C6—C7—H7120.2
O2—C1—O1126.02 (17)C7—C8—C9120.5 (3)
O2—C1—C2122.41 (16)C7—C8—H8119.7
O1—C1—C2111.57 (15)C9—C8—H8119.7
N1—C2—C1107.48 (14)C8—C9—C4120.5 (3)
N1—C2—C3111.26 (15)C8—C9—H9119.8
C1—C2—C3110.82 (15)C4—C9—H9119.8
N1—C2—H2A109.1O4—C10—O3120.46 (16)
C1—C2—H2A109.1O4—C10—C11118.87 (16)
C3—C2—H2A109.1O3—C10—C11120.67 (16)
C4—C3—C2115.14 (15)C12—C11—C10130.92 (17)
C4—C3—H3A108.5C12—C11—H11114.5
C2—C3—H3A108.5C10—C11—H11114.5
C4—C3—H3B108.5C11—C12—C13130.59 (17)
C2—C3—H3B108.5C11—C12—H12114.7
H3A—C3—H3B107.5C13—C12—H12114.7
C5—C4—C9119.13 (19)O5—C13—O6124.02 (17)
C5—C4—C3120.77 (18)O5—C13—C12115.88 (16)
C9—C4—C3119.97 (18)O6—C13—C12120.09 (16)
C4—C5—C6120.8 (2)
O2—C1—C2—N14.1 (2)C5—C6—C7—C80.0 (4)
O1—C1—C2—N1176.15 (15)C6—C7—C8—C90.6 (4)
O2—C1—C2—C3117.6 (2)C7—C8—C9—C40.3 (4)
O1—C1—C2—C362.1 (2)C5—C4—C9—C81.7 (3)
N1—C2—C3—C485.72 (19)C3—C4—C9—C8174.2 (2)
C1—C2—C3—C4154.75 (16)O4—C10—C11—C12174.2 (2)
C2—C3—C4—C5122.01 (19)O3—C10—C11—C125.4 (3)
C2—C3—C4—C962.1 (2)C10—C11—C12—C131.7 (4)
C9—C4—C5—C62.3 (3)C11—C12—C13—O5174.5 (2)
C3—C4—C5—C6173.65 (19)C11—C12—C13—O66.7 (3)
C4—C5—C6—C71.4 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H1···O5i0.821.782.5314 (19)151
O3—H3···O60.821.652.468 (2)176
N1—H1A···O4ii0.891.982.861 (2)170
N1—H1A···O3ii0.892.403.047 (2)130
N1—H1B···O6iii0.891.982.823 (2)159
N1—H1C···O2iv0.892.262.839 (2)123
N1—H1C···O5v0.892.473.283 (2)152
Symmetry codes: (i) x1, y+1, z1; (ii) x1/2, y+3/2, z1/2; (iii) x+3/2, y+1/2, z+1/2; (iv) x+1/2, y1/2, z1/2; (v) x1, y, z1.

Experimental details

Crystal data
Chemical formulaC9H12NO2+·C4H3O4
Mr281.26
Crystal system, space groupMonoclinic, P21/n
Temperature (K)123
a, b, c (Å)12.308 (3), 5.9942 (12), 18.061 (4)
β (°) 99.15 (3)
V3)1315.5 (5)
Z4
Radiation typeMo Kα
µ (mm1)0.11
Crystal size (mm)0.3 × 0.3 × 0.1
Data collection
DiffractometerBruker SMART CCD
diffractometer
Absorption correctionMulti-scan
(SADABS; Bruker, 1998)
Tmin, Tmax0.97, 0.99
No. of measured, independent and
observed [I > 2σ(I)] reflections
13028, 2704, 2250
Rint0.043
(sin θ/λ)max1)0.626
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.045, 0.146, 1.13
No. of reflections2704
No. of parameters183
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.34, 0.34

Computer programs: SMART (Bruker, 1999), SMART, SAINT (Bruker, 1999), SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), PLATON (Spek, 1999), SHELXL97.

Selected geometric parameters (Å, º) top
O1—C11.313 (2)C4—C51.381 (3)
O2—C11.209 (2)C4—C91.383 (3)
O3—C101.303 (2)C5—C61.391 (3)
O4—C101.229 (2)C6—C71.390 (5)
O5—C131.246 (2)C7—C81.378 (5)
O6—C131.276 (2)C8—C91.380 (3)
N1—C21.485 (2)C10—C111.497 (2)
C1—C21.524 (2)C11—C121.333 (3)
C2—C31.535 (3)C12—C131.501 (3)
C3—C41.513 (2)
O2—C1—O1126.02 (17)C8—C7—C6119.6 (2)
O2—C1—C2122.41 (16)C7—C8—C9120.5 (3)
O1—C1—C2111.57 (15)C8—C9—C4120.5 (3)
N1—C2—C1107.48 (14)O4—C10—O3120.46 (16)
N1—C2—C3111.26 (15)O4—C10—C11118.87 (16)
C1—C2—C3110.82 (15)O3—C10—C11120.67 (16)
C4—C3—C2115.14 (15)C12—C11—C10130.92 (17)
C5—C4—C9119.13 (19)C11—C12—C13130.59 (17)
C5—C4—C3120.77 (18)O5—C13—O6124.02 (17)
C9—C4—C3119.97 (18)O5—C13—C12115.88 (16)
C4—C5—C6120.8 (2)O6—C13—C12120.09 (16)
C7—C6—C5119.4 (3)
O2—C1—C2—N14.1 (2)C5—C6—C7—C80.0 (4)
O1—C1—C2—N1176.15 (15)C6—C7—C8—C90.6 (4)
O2—C1—C2—C3117.6 (2)C7—C8—C9—C40.3 (4)
O1—C1—C2—C362.1 (2)C5—C4—C9—C81.7 (3)
N1—C2—C3—C485.72 (19)C3—C4—C9—C8174.2 (2)
C1—C2—C3—C4154.75 (16)O4—C10—C11—C12174.2 (2)
C2—C3—C4—C5122.01 (19)O3—C10—C11—C125.4 (3)
C2—C3—C4—C962.1 (2)C10—C11—C12—C131.7 (4)
C9—C4—C5—C62.3 (3)C11—C12—C13—O5174.5 (2)
C3—C4—C5—C6173.65 (19)C11—C12—C13—O66.7 (3)
C4—C5—C6—C71.4 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H1···O5i0.821.782.5314 (19)151
O3—H3···O60.821.652.468 (2)176
N1—H1A···O4ii0.891.982.861 (2)170
N1—H1A···O3ii0.892.403.047 (2)130
N1—H1B···O6iii0.891.982.823 (2)159
N1—H1C···O2iv0.892.262.839 (2)123
N1—H1C···O5v0.892.473.283 (2)152
Symmetry codes: (i) x1, y+1, z1; (ii) x1/2, y+3/2, z1/2; (iii) x+3/2, y+1/2, z+1/2; (iv) x+1/2, y1/2, z1/2; (v) x1, y, z1.
 

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