Download citation
Download citation
link to html
Crystals of the title salt, [(C6H5NH3)]+·[(HOOC(CH2)CH(OH)COO)] or C6H8N+·C4H5O5, are built up from protonated anilinium residues and monodissociated DL-malate ions. The NH3+ group of the anilinium cation is ordered at room temperature. Rotation of the NH3+ group along the C(aromatic)—Nsp3 bond (often observed at room temperature in other anilinium salts) is prevented by N—H...O hydrogen bonds between the NH3+ group and the malate anions. The anions are connected by four O—H...O hydrogen bonds into two-dimensional sheets parallel to the (001) plane. The charged moieties, i.e. the anilinium cations and the sheets of hydrogen-bonded malate anions, form two-dimensional layers in which the phenyl rings of the anilinium residues lie perpendicular to the malate-ion sheets. The conformation of the monodissociated malate ion in the crystal is compared with that obtained from ab initio molecular-orbital calculations.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270103023837/gg1192sup1.cif
Contains datablocks anijab, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270103023837/gg1192Isup2.hkl
Contains datablock I

CCDC reference: 229115

Comment top

Crystals of anilinium organic and inorganic salts exhibit structural phase transitions induced by order/disorder transformations of the protonated amine group, NH3+. The potential energy barrier for rotation of the NH3+ group along the C(aromatic)—Nsp3 single bond is small, if the H atoms interact weakly with neighbouring ions or molecules. In this case, the NH3+ group exhibits rotation at room temperature, but this is inhibited at lower temperatures. Investigation of the title compound, (I), has its origin in our interest in the characterization of compounds that form multiple and different hydrogen-bonding systems (Janczak & Perpétuo, 2003, and references therein; Perpétuo & Janczak, 2003). Additionally, the geometry and conformation of (I) have been compared with the ab-initio fully optimized parameters calculated at the B3LYP/6–31 G(d,p) level (Frisch et al., 1995). The ab-initio molecular orbital (MO) calculations were carried out on isolated ions, i.e. te anilinium cation and monodissociated (DL)-malate anion, and the results are illustrated in Fig. 1.

Our X-ray study of (I) shows that the NH3+ group in the anilinium cations is ordered at room temperature; however, the malate anion may be disordered, as indicated by? the relatively high anisotropic displacement parameters of the C atoms. Nevertheless, some disorder models that have been tested for the malate anion show no disorder, and thus the relatively high displacement parameters of the atoms of the malate ion can be taken to indicate large molecular motion. Additionally, the powder diffraction data collected between room temperature and 90 K did not show evidence for any structural phase transition. The benzene ring of the anilinium cation (Fig. 2) (like that of other anilinium compounds) has a symmetry closer to C2v (mm) than to C6 h (6/mmm) (Colapietro et al., 1981, Sakal & Terauchi, 1981; Paixao et al., 2000). The distortion of the ring is not large but is significant, and involves bond distances as well as angles. The endocyclic C—C—C angle ipso to the substituent is larger than 120° (especially in the optimized molecule; Fig. 1 b) as expected from the σ-electron-withdrawing character of the NH3+ group (Domenicano & Murray-Rust, 1979). The aromatic C—C bonds involving the C atom ipso to the substituent, viz. C11—C12 and C11—C16, are shorter than the central C—C bonds of the ring, viz. C12—C13 and C15—C16. The differences in the C—C bonds within the ring in the crystal are greater than the optimized differences?. The C(aromatic)—Nsp3 distance is close to the lower band of the range reported for several anilinium salts (Allen et al., 1987).

The anilinium residue in the crystal of (I) is involved in three hydrogen bonds as a donor. The H atoms of the NH3+ group form N—H···O hydrogen bonds with three neighbouring monodissociated (DL)-malate anions (see Table 2).

The conformation of the carbon skeleton of the malate anion in (I) is syn [ψ = 179.7 (2)°], with the dissociated carboxyl group (COO) almost coplanar with the C2 and O5 atoms [ϕ2 = −8.8 (2)°]. The conformation of the carboxyl group (COOH) around the terminal C—C bond is clinal [χ = 77.7 (2)°]. The ψ, ϕ2 and χ torsion angles in (I) (ψ = C1—C2—C3—C4, ϕ2 = O1—C1—C2—O5 and χ = C2—C3—C4—O4) describe the conformation of the malate ion as well as the conformation of the malic acid (Sluis & Kroon, 1985; 1989). In the optimized malate ion, the values of ψ, ϕ2 and χ are −177.8, −3.9 and 61.7°, respectively. Thus the conformation of the carbon skeleton of the optimized malate ion is anti. The optimized value of ϕ2 is smaller than the angle in (I), and the O1—C1—C2—O5—H5o fragment deviates less from the plane than it does in (I) because of the formation of the intramolecular O5—H5o···O1 hydrogen bond [O5—H5o = 0.947 Å, H5o···O1 = 1.872 Å and O—H···O = 125.6°; for comparison with the X-ray geometry of this hydrogen bond, see Table 2]. The rotation of the terminal COOH group is greater in the crystal than in the optimized ion [χ = 61.7 and 77.7 (2)° in the optimized ion and in the crystal] because of the interaction of this group with the hydroxy group of a neighbouring malate ion and the formation of the O5—H5o···O4i hydrogen bond. The optimized angle in the carboxy group (O1—C1—O2) is greater, and the angle in the nondissociated carboxy group (O3—C4—O4) is smaller, than the corresponding angle in (I). These differences are explained by the steric effect of the lone-pair electron predicted by the valence-shell electron-pair repulsion model (VSEPR; Gillespie, 1963, 1992). Atom O5 is involved in two hydrogen bonds, one as a donor to a neighbouring malate anion and one as an acceptor to the NH3+ group of the anilinium residue.

The C1—C2, C2—C3 and C3—C4 bond lengths obtained from the X-ray analysis of (I) are shorter than the optimized bond lengths. A search of the Cambridge Structural Database (CSD; Allen, 2002) for structures containing the malate anion or malic acid shows that in the crystal of (DL)-malic acid (Sluis & Kroon, 1985), as well as in the crystal of (L)-malic acid (Sluis & Kroon, 1989), these C—C bonds range from 1.499 (4) to 1.529 (4) Å. The C—O bond distances in the dissociated carboxy group ?are intermediate between typical single and double bond lengths, indicating? the delocalization of the π electron over both C—O bonds. The O1—C1—O2 angle of the dissociated carboxy group (COO) is greater than the O3—C4—O4 angle of the carboxyl group (COOH) in both the crystal and the optimized malate anion because of the steric effect of the lone-pair electron on atoms O1 and O2 atoms in relation to the non-dissociated COOH group.

Each monodissociated malate anion is connected by O—H···O hydrogen bonds to four neighbouring malate ions, thus forming a sheet that is located parallel to the (001) plane in the crystal. The anilinium cations are linked by N—H···O hydrogen bonds to three malate ions in the sheet, thus forming two-dimensional layers. The benzene rings of the anilinium residues are almost perpendicular to the sheet of hydrogen-bonded malate ions. Two anilinium–malate layers, connected via hydrogen bonds, are oriented in an alternating face-to-face and back-to-back pattern (Fig. 3). The rings of the anilinium moieties are partially overlapping and interact slightly via the ππ clouds (separated by about 3.66 Å along the stack) formed by two face-to-face-oriented layers of interconnected anilinium and malate residues.

Experimental top

Aniline was added to a solution (10%) of (DL)-malic acid and the resulting solution was evaporated slowly. After several days, colourless crystals of (I) appeared.

Computing details top

Data collection: Kuma KM-4 CCD Software (Kuma, 2000); cell refinement: Kuma KM-4 CCD Software; data reduction: Kuma KM-4 CCD Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990a); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 1990b); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. Results of the optimized ab-initio calculations for the monodissociated malate anion and for the anilinium cation. Geometric parameters are in Å and °.
[Figure 2] Fig. 2. The molecular structure of (I), showing 50% probability displacement ellipsoids. H atoms are shown as spheres of arbitrary radii.
[Figure 3] Fig. 3. The crystal packing of (I), showing the alternating arrangment of back-to-back and face-to-face layers of the hydrogen-bonded anilinium–malate residues. Dashed lines represent hydrogen bonds and H atoms have been omitted for clarity.
anilinium monohydrogen (DL)-malate top
Crystal data top
C6H8N+·C4H5O5Z = 2
Mr = 227.21F(000) = 240
Triclinic, P1Dx = 1.415 Mg m3
Dm = 1.41 Mg m3
Dm measured by floatation
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 6.180 (1) ÅCell parameters from 1339 reflections
b = 7.545 (2) Åθ = 3.2–26.2°
c = 12.425 (2) ŵ = 0.11 mm1
α = 91.23 (3)°T = 293 K
β = 102.27 (3)°Parallelepiped, colourless
γ = 108.80 (3)°0.28 × 0.25 × 0.21 mm
V = 533.4 (2) Å3
Data collection top
Kuma KM-4 with CCD detector
diffractometer
2123 independent reflections
Radiation source: fine-focus sealed tube1339 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.011
Detector resolution: 1024x1024 with blocks 2x2 pixels mm-1θmax = 26.2°, θmin = 3.2°
ω–scanh = 67
Absorption correction: analytical
face-indexed, SHELXTL (Sheldrick, 1990b)
k = 98
Tmin = 0.964, Tmax = 0.978l = 1515
5133 measured reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.039H-atom parameters constrained
wR(F2) = 0.107 w = 1/[σ2(Fo2) + (0.0443P)2 + 0.058P]
where P = (Fo2 + 2Fc2)/3
S = 1.09(Δ/σ)max = 0.001
2113 reflectionsΔρmax = 0.25 e Å3
164 parametersΔρmin = 0.25 e Å3
0 restraintsExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.078 (9)
Crystal data top
C6H8N+·C4H5O5γ = 108.80 (3)°
Mr = 227.21V = 533.4 (2) Å3
Triclinic, P1Z = 2
a = 6.180 (1) ÅMo Kα radiation
b = 7.545 (2) ŵ = 0.11 mm1
c = 12.425 (2) ÅT = 293 K
α = 91.23 (3)°0.28 × 0.25 × 0.21 mm
β = 102.27 (3)°
Data collection top
Kuma KM-4 with CCD detector
diffractometer
2123 independent reflections
Absorption correction: analytical
face-indexed, SHELXTL (Sheldrick, 1990b)
1339 reflections with I > 2σ(I)
Tmin = 0.964, Tmax = 0.978Rint = 0.011
5133 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0390 restraints
wR(F2) = 0.107H-atom parameters constrained
S = 1.09Δρmax = 0.25 e Å3
2113 reflectionsΔρmin = 0.25 e Å3
164 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
O10.3701 (2)0.04190 (15)0.84679 (11)0.0565 (4)
O20.7578 (2)0.17753 (15)0.88424 (12)0.0650 (4)
C10.5713 (3)0.03878 (19)0.85793 (15)0.0505 (4)
C20.5900 (3)0.1505 (2)0.8274 (2)0.0906 (9)
H20.63570.13860.75630.136*
O50.3827 (2)0.29502 (15)0.80690 (13)0.0720 (4)
H5O0.27520.25360.80680.108*
C30.7876 (3)0.1907 (2)0.9054 (2)0.0900 (8)
H3A0.76380.18720.98000.108*
H3B0.93500.09350.90470.108*
C40.8024 (3)0.3806 (2)0.87397 (18)0.0571 (5)
O30.7225 (2)0.50120 (17)0.94000 (12)0.0701 (4)
H3O0.73100.60320.92130.105*
O40.8850 (3)0.41506 (19)0.80036 (13)0.0780 (5)
N10.1637 (2)0.31137 (18)0.79078 (11)0.0479 (4)
H1N0.03250.27770.81540.059 (5)*
H2N0.24530.43180.81340.083 (7)*
H3N0.24980.24060.81710.093 (8)*
C110.1044 (3)0.2854 (2)0.67098 (14)0.0465 (4)
C120.1272 (4)0.2229 (3)0.61420 (17)0.0689 (6)
H120.24720.19800.65180.083*
C130.1777 (5)0.1979 (4)0.4998 (2)0.0886 (7)
H130.33370.15390.46040.106*
C140.0033 (5)0.2365 (3)0.4438 (2)0.0870 (7)
H140.03940.22000.36690.104*
C150.2228 (5)0.2992 (3)0.5016 (2)0.0859 (7)
H150.34260.32520.46380.103*
C160.2796 (4)0.3256 (3)0.61624 (17)0.0686 (6)
H160.43590.37020.65510.082*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0452 (7)0.0419 (7)0.0835 (9)0.0203 (5)0.0081 (6)0.0061 (6)
O20.0517 (8)0.0302 (6)0.1158 (11)0.0138 (6)0.0252 (7)0.0012 (6)
C10.0492 (11)0.0333 (9)0.0714 (12)0.0169 (8)0.0141 (9)0.0081 (8)
C20.0488 (12)0.0360 (11)0.172 (3)0.0179 (9)0.0090 (14)0.0160 (12)
O50.0480 (8)0.0350 (7)0.1193 (12)0.0131 (6)0.0067 (7)0.0074 (7)
C30.0633 (13)0.0347 (10)0.154 (2)0.0201 (9)0.0151 (14)0.0147 (12)
C40.0443 (10)0.0388 (10)0.0861 (14)0.0199 (8)0.0019 (10)0.0020 (9)
O30.0717 (9)0.0429 (7)0.1077 (11)0.0245 (6)0.0380 (8)0.0027 (7)
O40.1031 (12)0.0531 (8)0.0852 (10)0.0309 (8)0.0291 (9)0.0166 (7)
N10.0432 (8)0.0369 (8)0.0620 (10)0.0140 (7)0.0080 (7)0.0007 (6)
C110.0510 (10)0.0371 (9)0.0527 (10)0.0195 (7)0.0069 (8)0.0028 (7)
C120.0548 (12)0.0766 (14)0.0691 (14)0.0223 (10)0.0014 (10)0.0027 (10)
C130.0793 (17)0.0981 (18)0.0734 (16)0.0314 (14)0.0158 (13)0.0014 (13)
C140.116 (2)0.0833 (17)0.0611 (14)0.0379 (16)0.0119 (15)0.0108 (12)
C150.0940 (19)0.0847 (17)0.0771 (17)0.0188 (14)0.0330 (15)0.0059 (13)
C160.0587 (12)0.0733 (14)0.0683 (14)0.0140 (10)0.0162 (10)0.0000 (10)
Geometric parameters (Å, º) top
O1—C11.230 (2)N1—H1N0.8900
O2—C11.256 (2)N1—H2N0.8900
C1—C21.516 (2)N1—H3N0.8900
C2—O51.358 (2)C11—C161.355 (3)
C2—C31.507 (2)C11—C121.375 (3)
C2—H20.9800C12—C131.384 (3)
O5—H5O0.8200C12—H120.9300
C3—C41.513 (2)C13—C141.362 (3)
C3—H3A0.9700C13—H130.9300
C3—H3B0.9700C14—C151.351 (3)
C4—O41.199 (2)C14—H140.9300
C4—O31.288 (2)C15—C161.386 (3)
O3—H3O0.8200C15—H150.9300
N1—C111.448 (2)C16—H160.9300
O1—C1—O2126.53 (13)H1N—N1—H2N109.5
O1—C1—C2115.36 (15)C11—N1—H3N109.5
O2—C1—C2117.91 (15)H1N—N1—H3N109.5
O5—C2—C3113.78 (16)H2N—N1—H3N109.5
O5—C2—C1114.18 (15)C16—C11—C12120.84 (18)
C3—C2—C1112.69 (14)C16—C11—N1119.15 (16)
O5—C2—H2105.0C12—C11—N1120.00 (17)
C3—C2—H2105.0C11—C12—C13118.5 (2)
C1—C2—H2105.0C11—C12—H12120.8
C2—O5—H5O109.5C13—C12—H12120.8
C2—C3—C4111.90 (14)C14—C13—C12121.2 (2)
C2—C3—H3A109.2C14—C13—H13119.4
C4—C3—H3A109.2C12—C13—H13119.4
C2—C3—H3B109.2C15—C14—C13119.0 (2)
C4—C3—H3B109.2C15—C14—H14120.5
H3A—C3—H3B107.9C13—C14—H14120.5
O4—C4—O3123.62 (14)C14—C15—C16121.2 (2)
O4—C4—C3125.4 (2)C14—C15—H15119.4
O3—C4—C3110.97 (18)C16—C15—H15119.4
C4—O3—H3O109.5C11—C16—C15119.2 (2)
C11—N1—H1N109.5C11—C16—H16120.4
C11—N1—H2N109.5C15—C16—H16120.4
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O5—H5O···O10.822.132.608 (3)117
O5—H5O···O4i0.822.312.895 (3)129
O3—H3O···O2ii0.821.782.595 (3)178
N1—H3N···O10.891.892.757 (3)165
N1—H2N···O5iii0.891.972.821 (2)159
N1—H1N···O2i0.892.002.884 (3)172
Symmetry codes: (i) x1, y, z; (ii) x, y1, z; (iii) x, y+1, z.

Experimental details

Crystal data
Chemical formulaC6H8N+·C4H5O5
Mr227.21
Crystal system, space groupTriclinic, P1
Temperature (K)293
a, b, c (Å)6.180 (1), 7.545 (2), 12.425 (2)
α, β, γ (°)91.23 (3), 102.27 (3), 108.80 (3)
V3)533.4 (2)
Z2
Radiation typeMo Kα
µ (mm1)0.11
Crystal size (mm)0.28 × 0.25 × 0.21
Data collection
DiffractometerKuma KM-4 with CCD detector
diffractometer
Absorption correctionAnalytical
face-indexed, SHELXTL (Sheldrick, 1990b)
Tmin, Tmax0.964, 0.978
No. of measured, independent and
observed [I > 2σ(I)] reflections
5133, 2123, 1339
Rint0.011
(sin θ/λ)max1)0.621
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.039, 0.107, 1.09
No. of reflections2113
No. of parameters164
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.25, 0.25

Computer programs: Kuma KM-4 CCD Software (Kuma, 2000), Kuma KM-4 CCD Software, SHELXS97 (Sheldrick, 1990a), SHELXL97 (Sheldrick, 1997), SHELXTL (Sheldrick, 1990b), SHELXL97.

Selected geometric parameters (Å, º) top
O1—C11.230 (2)C3—C41.513 (2)
O2—C11.256 (2)C4—O41.199 (2)
C1—C21.516 (2)C4—O31.288 (2)
C2—O51.358 (2)N1—C111.448 (2)
C2—C31.507 (2)
O1—C1—O2126.53 (13)C3—C2—C1112.69 (14)
O1—C1—C2115.36 (15)C2—C3—C4111.90 (14)
O2—C1—C2117.91 (15)O4—C4—O3123.62 (14)
O5—C2—C3113.78 (16)O4—C4—C3125.4 (2)
O5—C2—C1114.18 (15)O3—C4—C3110.97 (18)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O5—H5O···O10.822.132.608 (3)117
O5—H5O···O4i0.822.312.895 (3)129
O3—H3O···O2ii0.821.782.595 (3)178
N1—H3N···O10.891.892.757 (3)165
N1—H2N···O5iii0.891.972.821 (2)159
N1—H1N···O2i0.892.002.884 (3)172
Symmetry codes: (i) x1, y, z; (ii) x, y1, z; (iii) x, y+1, z.
 

Follow Acta Cryst. C
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds