4-Carboxy-anilinium (2R,3R)-tartrate and a redetermination of the α-polymorph of 4-amino-benzoic acid

Article abstract of DOI:10.1107/S0108270107022469

In the title compounds, 4-carboxy-anilinium (2R,3R)-tartrate, C7H8NO2 ⁺·C4H5O6 ^-, (I), and 4-amino-benzoic acid, C7H7NO2, (II), the carboxyl planes of the 4-carboxy-anilinium cations/4-amino-benzoic acid are twisted from the aromatic plane. In (I), the characteristic head-to-tail inter-actions are observed through the tartrate anions, forming two C 2 ²(7) chain motifs propagating parallel to the a and c axes of the unit cell. Also, the tartrate anions are connected through two primary C 1 ¹(6) and C 1 ¹(7) chain motifs, leading to a secondary R 4 ⁴(22) ring motif. In (II), head-to-tail inter-action is seen through a discrete D 1 ¹(2) motif and carboxyl group dimerization is observed through centrosymmetrically related R 2 ²(8) motifs around the inversion centres of the unit cell. The crystal structures of both compounds are stabilized by intricate three-dimensional hydrogen-bonding networks. Alternate hydro-phobic and hydro-philic layers are observed in (I) as a result of a column-like arrangement of the anions and the aromatic rings of the cations. International Union of Crystallography 2007.

Full text of DOI:10.1107/S0108270107022469

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
of diffractometer data for the ꢀ-form of this compound,
(II), stimulated us to carry out the redetermination of this
structure.
ISSN 0108-2701
4-Carboxyanilinium (2R,3R)-tartrate
and a redetermination of the a-poly-
morph of 4-aminobenzoic acid
PABA complexes such as 4-carboxyphenylammonium
nitrate, 4-carboxyphenylammonium perchlorate monohydrate
and bis(4-carboxyphenylammonium) sulfate (Athimoolam &
Natarajan, 2006), have already been studied in our laboratory
to understand their structure±extension properties via their
linear and cyclic hydrogen-bonding associations. Also, the
structures of 4-carboxyanilinium dihydrogenmonoarsenate
monohydrate (Tordjman et al., 1988), 2,4,6-trinitrobenzoic
acid 4-aminobenzoic acid monohydrate (Lynch et al., 1992),
bis(4-aminobenzoic acid)dichlorocadmium(II) (Le Fur &
Masse, 1996) and bis(4-aminobenzoic acid)silver(I) nitrate
(Wang et al., 2004) have been reported previously. Hu and co-
workers have already reported the structure of PABA with
tartaric acid in hydrated form (Hu et al., 2002). We present
here the crystal structure of an anhydrous form of the PABA±
tartaric acid complex, (I).
The asymmetric parts of (I) and (II) consist of two crys-
tallographically independent PABA molecules oriented with
angles of 1.7 (3) and 38.4 (1)ꢀ, respectively, between them
(Figs. 1 and 2). Protonation on the N site of the PABA cation
and deprotonation on the ±COOH group of the anion in (I)
are evident from the CÐN and CÐO bond distances (Table 1).
Twisting out of the carboxyl plane from the aromatic ring
plane is a common feature found in PABA complexes [in 27
complexes of PABA adducts in the Cambridge Structural
Database (CSD, Version 5.28; Allen, 2002)]. The angles of this
S. Athimoolam* and S. Natarajan
Department of Physics, Madurai Kamaraj University, Madurai 625 021, India
Correspondence e-mail: xrdsopmku@yahoo.com
Received 2 April 2007
Accepted 7 May 2007
Online 9 August 2007
In the title compounds, 4-carboxyanilinium (2R,3R)-tartrate,
+
C7H8NO2 ÁC4H5O6 , (I), and 4-aminobenzoic acid, C7H7NO2,
(II), the carboxyl planes of the 4-carboxyanilinium cations/4-
aminobenzoic acid are twisted from the aromatic plane. In (I),
the characteristic head-to-tail interactions are observed
through the tartrate anions, forming two C22(7) chain motifs
propagating parallel to the a and c axes of the unit cell. Also,
the tartrate anions are connected through two primary C11(6)
and C11(7) chain motifs, leading to a secondary R44(22) ring
motif. In (II), head-to-tail interaction is seen through a
discrete D11(2) motif and carboxyl group dimerization is
observed through centrosymmetrically related R22(8) motifs
around the inversion centres of the unit cell. The crystal
structures of both compounds are stabilized by intricate three-
dimensional hydrogen-bonding networks. Alternate hydro-
phobic and hydrophilic layers are observed in (I) as a result of
a column-like arrangement of the anions and the aromatic
rings of the cations.
Comment
4-Aminobenzoic acid (PABA) is an essential biological mol-
ecule, acting as a bacterial cofactor involved in the synthesis of
folic acid (Robinson, 1966). PABA is also a starting material in
the synthesis of target esters, salts, folic acid, azo dyes and
many other organic compounds. It is used in medicine for
preparing local anaesthetics and ointments. It helps to protect
the skin from sunburn and cancer. Fibrotic skin disorders can
also be treated with PABA (Osgood et al., 1982). As PABA
can donate and also accept hydrogen, it has proved to be a
versatile reagent for structure extension by linear hydrogen-
bonding associations, through both the carboxylic acid and
amine functional groups. The crystallographic study of PABA
compounds was started by Pant (1965), who studied the crystal
structure of 4-amino-3,5-dibromobenzoic acid. Later, Lai &
Marsh (1967) studied this structure extensively using photo-
graphic/visual data. In fact, PABA exists as two different
polymorphs, viz. the ꢀ- and ꢁ-forms. The ꢁ-form has recently
been reinvestigated by Gracin & Fischer (2005). The absence
Figure 1
The molecular structure of (I), showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 50% probability level and H
atoms not involved in the hydrogen bonds (dashed lines) have been
omitted for clarity.
o514 # 2007 International Union of Crystallography
DOI: 10.1107/S0108270107022469
Acta Cryst. (2007). C63, o514±o517

organic compounds
twisting are 1.1 (2) and 6.8 (2)ꢀ in (I), and 3.0 (4) and 4.3 (4)ꢀ
in (II).
dimerization is observed through centrosymmetrically related
R22(8) motifs (in both residues in the asymmetric unit) around
the inversion centres of the unit cell. Hence, in short, the
crystal packing of (II) can be readily described with three
primary motifs [two R22(8) and one D11(2)] and two discrete
secondary motifs [D32(7) and D33(19)] (Table 3 and Fig. 4).
Alternate hydrophobic and hydrophilic layers are observed
in (I) as a result of the column-like arrangement of the
aromatic rings of the cations and the anions. Each tartrate
anion forms a self-association of S(5) motif via OÐHÁ Á ÁO
intramolecular bonds. Even though tartrates form extensive
intermolecular hydrogen bonds between themselves and with
PABA, it is more sensible to discuss the characteristic
As discussed above, the structure±extension property of
PABA via hydrogen bonds is recognized as a possible tool for
promoting cocrystallization, with the aim of designing
noncentrosymmetric organic materials (Etter & Frankenbach,
1989). However, among the many reported adducts of PABA,
only a few have been found to crystallize in noncentrosym-
metric space groups (only four out of 27 complexes of PABA
adducts in the CSD), and complex (I) is another such case.
In (II), the bond distances and angles (Table 3) are in
agreement with the reported values (Lai & Marsh, 1967).
Even though the molecular structure of (II) is already known,
the aim of the present work is to elucidate the structure with
precision, and to study the crystal packing of the molecule via
hydrogen bonds and their visualization through graph-set
notation (Etter et al., 1990; Bernstein et al., 1995).
As discussed in our previous publication (Athimoolam &
Natarajan, 2006), head-to-tail hydrogen-bonding association
+
(head = NH2/NH3 and tail = COOH) and carboxyl group
dimerization are characteristic interactions found between the
PABA residues in many PABA complexes in the CSD. In (I),
these interactions are observed through the anions because of
dominant hydrogen-bonding sites in the tartrates, and corre-
spondingly the crystal packing can be described by an intricate
three-dimensional hydrogen-bonding network (Fig. 3). In (II),
head-to-tail interaction is seen through a discrete D11(2) motif
via an N14Á Á ÁO2A hydrogen bond and carboxyl group
Figure 4
A packing diagram for (II), viewed down the b axis. Hydrogen bonds are
shown as dashed lines.
Figure 2
The molecular structure of (II), showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 50% probability level and H
atoms are shown as small spheres of arbitrary radii. Hydrogen bonds are
shown as dashed lines.
Figure 5
A view of the cations in (I) connected through the tartrate anions,
showing the C22(7) chain motifs and R33(12) ring motifs. Hydrogen bonds
are shown as dashed lines. [Symmetry codes: (i) x, y, z 1; (ii) x + 1, y, z;
(iii) x + 1, y, z 1.]
Figure 3
A packing diagram for (I), viewed down the a axis. Hydrogen bonds are
shown as dashed lines.
+
ꢁ
Acta Cryst. (2007). C63, o514±o517
Athimoolam and Natarajan
C7H8NO2 ÁC4H5O6 and C7H7NO2 o515

organic compounds
Re®nement
hydrogen-bonding features than all the intricate hydrogen
bonds (Table 4). The NH3+ group of the cationic residues of (I)
and (II) form two sets of C22(7) chain motifs through the
tartrate anions via NÐHÁ Á ÁO hydrogen bonds. Also, the
tartrate anions are themselves connected via OÐHÁ Á ÁO bonds
of another C22(7) chain motif. One of the two C22(7) chain
motifs of the NÐHÁ Á ÁO hydrogen bonds and the OÐHÁ Á ÁO
C22(7) chain motif lead to a ring of R33(12) motif in both
cationic residues (Fig. 5). Fig. 6 shows the aggregation of the
tartrates through OÐHÁ Á ÁO chain motifs of C11(6) and C11(7)
running along the a and c axes of the unit cell, respectively.
These chain motifs form a closed secondary R44(22) ring motif
in both anions.
R[F2 > 2ꢃ(F2)] = 0.039
wR(F2) = 0.106
S = 1.08
2721 re¯ections
371 parameters
1 restraint
H-atom parameters constrained
3
Ê
Áꢄmax = 0.29 e A
3
Ê
0.28 e A
Áꢄmin
=
Table 1
Selected geometric parameters (A, ) for (I).
ꢀ
Ê
C111ÐO1A
C111ÐO1B
C14ÐN14
C211ÐO2A
C211ÐO2B
C24ÐN24
1.196 (7)
1.318 (7)
1.464 (6)
1.205 (10)
1.344 (10)
1.476 (5)
1.236 (5)
C1CÐO2C
C4CÐO5C
C4CÐO6C
C1DÐO1D
C1DÐO2D
C4DÐO5D
C4DÐO6D
1.261 (5)
1.202 (5)
1.306 (5)
1.232 (5)
1.276 (5)
1.219 (5)
1.301 (5)
C1CÐO1C
C12ÐC11ÐC111ÐO1B 1.3 (7)
C22ÐC21ÐC211ÐO2B 6.2 (8)
Table 2
Hydrogen-bond geometry (A, ) for (I).
ꢀ
Ê
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
O1BÐH1BÁ Á ÁO5Ci
O1BÐH1BÁ Á ÁO4Ci
N14ÐH14AÁ Á ÁO2Dii
N14ÐH14BÁ Á ÁO3Di
N14ÐH14CÁ Á ÁO1Diii
O2BÐH2BÁ Á ÁO5D
N24ÐH24AÁ Á ÁO2Civ
N24ÐH24CÁ Á ÁO3C
N24ÐH24BÁ Á ÁO1Cv
O3CÐH3CÁ Á ÁO1A
O4CÐH4CÁ Á ÁO1Cvi
O6CÐH6CÁ Á ÁO2Cv
O3DÐH3DÁ Á ÁO5Dvi
O4DÐH4DÁ Á ÁO2Cvii
O6DÐH6DÁ Á ÁO2Dii
0.82
0.82
0.89
0.89
0.89
0.82
0.89
0.89
0.89
0.82
0.82
0.82
0.82
0.82
0.82
2.20
2.25
1.91
1.93
1.81
2.20
2.63
1.92
1.89
2.11
2.12
1.80
2.11
2.06
1.70
2.901 (6)
2.949 (6)
2.790 (5)
2.788 (4)
2.687 (4)
2.914 (6)
3.490 (5)
2.787 (5)
2.737 (5)
2.841 (5)
2.877 (5)
2.608 (4)
2.715 (4)
2.782 (4)
2.515 (4)
143
143
170
163
168
145
164
166
159
149
154
171
131
146
175
Figure 6
A view showing the aggregation of anions in (I) through the primary
C11(6) and C11(7) tartrate graph-set motifs propagating along the a and c
axes, respectively, and the secondary R44(22) ring motif. Hydrogen bonds
are shown as dashed lines. [Symmetry codes: (i) x 1, y, z; (ii) x, y, z 1.]
Symmetry codes: (i) x ‡ 1; y; z; (ii) x; y; z 1; (iii) x ‡ 1; y; z 1; (iv) x ‡ 1; y; z ‡ 1; (v)
1
2
x; y; z ‡ 1; (vi) x 1; y; z; (vii) x; y
; z.
Experimental
Compound (I) was crystallized from an aqueous solution containing
4-aminobenzoic acid and (2R,3R)-tartaric acid in a 1:1 stochiometric
ratio at room temperature by slow evaporation. Compound (II) was
crystallized from a saturated aqueous solution of 4-aminobenzoic
acid.
Compound (II)
Crystal data
3
Ê
V = 1327.06 (13) A
C7H7NO2
Mr = 137.14
Z = 8
Mo Kꢀ radiation
Monoclinic, P21=n
1
Compound (I)
Ê
a = 18.5712 (8) A
ꢂ = 0.10 mm
T = 293 (2) K
Ê
b = 3.8431 (3) A
Crystal data
+
Ê
c = 18.6321 (9) A
0.23 Â 0.14 Â 0.12 mm
Ê
V = 1225.0 (12) A
ꢁ = 93.670 (11)ꢀ
3
C7H8NO2 ÁC4H5O6
Mr = 287.22
Monoclinic, P21
Ê
a = 6.021 (4) A
Ê
b = 28.789 (11) A
c = 7.426 (5) A
ꢁ = 107.89 (4)ꢀ
Z = 4
Mo Kꢀ radiation
Data collection
1
ꢂ = 0.14 mm
T = 293 (2) K
Nonius MACH-3 sealed-tube
diffractometer
Absorption correction: scan
(North et al., 1968)
Tmin = 0.945, Tmax = 0.985
3787 measured re¯ections
2845 independent re¯ections
1746 re¯ections with I > 2ꢃ(I)
Rint = 0.038
3 standard re¯ections
frequency: 60 min
intensity decay: none
Ê
0.22 Â 0.15 Â 0.13 mm
Data collection
Nonius MACH-3 sealed-tube
diffractometer
Absorption correction: scan
(North et al., 1968)
Tmin = 0.930, Tmax = 0.981
3083 measured re¯ections
2721 independent re¯ections
2127 re¯ections with I > 2ꢃ(I)
Rint = 0.091
3 standard re¯ections
frequency: 60 min
intensity decay: none
Re®nement
R[F2 > 2ꢃ(F2)] = 0.066
wR(F2) = 0.227
S = 1.17
183 parameters
H-atom parameters constrained
3
Ê
Áꢄmax = 0.37 e A
3
Ê
0.27 e A
2845 re¯ections
Áꢄmin
=
+
ꢁ
o516 Athimoolam and Natarajan
C7H8NO2 ÁC4H5O6 and C7H7NO2
Acta Cryst. (2007). C63, o514±o517

organic compounds
Table 3
Selected geometric parameters (A, ) for (II).
Crystal Diffractometer facility at the School of Physics,
Madurai Kamaraj University, Madurai, through the FIST
programme. The authors also thank the UGC for the DRS
programme.
ꢀ
Ê
C111ÐO1A
C111ÐO1B
C14ÐN14
1.230 (4)
1.318 (4)
1.372 (5)
C211ÐO2A
C211ÐO2B
C24ÐN24
1.254 (4)
1.298 (4)
1.372 (5)
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: AV3090). Services for accessing these data are
described at the back of the journal.
C16ÐC11ÐC111ÐO1B
1.3 (5)
C22ÐC21ÐC211ÐO2B
3.0 (6)
Table 4
Hydrogen-bond geometry (A, ) for (II).
ꢀ
Ê
References
Allen, F. H. (2002). Acta Cryst. B58, 380±388.
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
Athimoolam, S. & Natarajan, S. (2006). Acta Cryst. C62, o612±o617.
Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem.
Int. Ed. Engl. 34, 1555±1573.
Bruker (2000). SHELXTL/PC. Version 6.10. Bruker AXS Inc., Madison,
Wisconsin, USA.
Enraf±Nonius (1994). CAD-4 EXPRESS. Version 5.1/1.2. Enraf±Nonius,
Delft, The Netherlands.
Etter, M. C. & Frankenbach, G. A. (1989). Chem. Mater. 1, 10±12.
Etter, M. C., MacDonald, J. C. & Bernstein, J. (1990). Acta Cryst. B46, 256±262.
Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565.
Gracin, S. & Fischer, A. (2005). Acta Cryst. E61, o1242±o1244.
Harms, K. & Wocadlo, S. (1995). XCAD4. University of Marburg, Germany.
Hu, Z., Liu, J., Shen, L., Xu, D. & Xu, Y. (2002). J. Chem. Crystallogr. 32, 525±
527.
Lai, T. F. & Marsh, R. E. (1967). Acta Cryst. 22, 885±893.
Le Fur, Y. & Masse, R. (1996). Acta Cryst. C52, 2183±2185.
Lynch, D. E., Smith, G., Byriel, K. A. & Kennard, C. H. L. (1992). Acta Cryst.
C48, 533±536.
O1BÐH1BÁ Á ÁO1Ai
N14ÐH14AÁ Á ÁO2A
O2BÐH2BÁ Á ÁO2Aii
N24ÐH24AÁ Á ÁO1Aiii
0.82
0.86
0.82
0.86
1.83
2.57
1.81
2.13
2.650 (4)
3.369 (5)
2.616 (4)
2.969 (4)
172
154
166
165
1
2
Symmetry codes: (i) x ‡ 2; y; z ‡ 1; (ii) x ‡ 1; y; z ‡ 1; (iii) x
,
y ‡ 12,
z ‡ 12.
All H atoms were positioned geometrically and re®ned using a
Ê
riding model, with CÐH = 0.93 (aromatic CH) and 0.98 A (±CH),
Ê
Ê
OÐH = 0.82 A and NÐH = 0.89 A, and with Uiso(H) = 1.2±
1.5Ueq(parent). In compound (I), in addition to the 2721 unique
re¯ections, 109 Friedel pairs were measured. However, owing to the
absence of atoms with signi®cant anomalous dispersion effects, these
data were merged.
For both compounds, data collection: CAD-4 EXPRESS (Enraf±
Nonius, 1994); cell re®nement: CAD-4 EXPRESS; data reduction:
XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve struc-
ture: SHELXTL/PC (Bruker, 2000); program(s) used to re®ne
structure: SHELXTL/PC; molecular graphics: ORTEP-3 (Farrugia,
1997), Mercury (Version 1.4.1; Macrae et al., 2006) and PLATON
(Spek, 2003); software used to prepare material for publication:
SHELXTL/PC.
Macrae, C. F., Edgington, P. R., McCabe, P., Pidcock, E., Shields, G. P., Taylor,
R., Towler, M. & van de Streek, J. (2006). J. Appl. Cryst. 39, 453±457.
North, A. C. T., Phillips, D. C. & Mathews, F. S. (1968). Acta Cryst. A24, 351±
359.
Osgood, P. J., Moss, S. H. & Davies, D. J. (1982). J. Invest. Dermatol. 79, 354±
357.
Pant, A. K. (1965). Acta Cryst. 19, 440±448.
Robinson, F. A. (1966). The Vitamin Co-factors of Enzyme Systems, pp. 541±
662. London: Pergamon.
Spek, A. L. (2003). J. Appl. Cryst. 36, 7±13.
Tordjman, I., Masse, R. & Guitel, J. C. (1988). Acta Cryst. C44, 2057±2059.
Wang, R., Hong, M. C., Luo, J., Jiang, F., Han, L., Lin, Z. & Cao, R. (2004).
Inorg. Chim. Acta, 357, 103±108.
The authors thank the Department of Science and Tech-
nology, Government of India, for establishing the Single-
+
ꢁ
Acta Cryst. (2007). C63, o514±o517
Athimoolam and Natarajan
C7H8NO2 ÁC4H5O6 and C7H7NO2 o517