Download citation
Download citation
link to html
A new polymorph of bis­(2-amino­pyridinium) fumarate–fum­aric acid (1/1), 2C5H7N2+·C4H2O42−·C4H4O4, was obtained and its crystal structure determined by powder X-ray diffraction. The new polymorph (form II) crystallizes in the triclinic system (space group P\overline{1}), while the previous reported polymorph [form I; Ballabh, Trivedi, Dastidar & Suresh (2002). CrystEngComm, 4, 135–142; Büyükgüngör, Odabaşoğlu, Albayrak & Lönnecke (2004). Acta Cryst. C60, o470–o472] is monoclinic (space group P21/c). In both forms I and II, the asymmetric unit consists of one 2-amino­pyridinium cation, half a fumaric acid mol­ecule and half a fumarate dianion. The fumarate dianion is involved in hydrogen bonding with two neighbouring 2-amino­pyridinium cations to form a hydrogen-bonded trimer in both forms. In form II, the hydrogen-bonded trimers are inter­linked across centres of inversion via pairs of N—H...O hydrogen bonds, whereas such trimers are joined via single N—H...O hydrogen bonds in form I, leading to different packing modes for forms I and II. The results demonstrate the relevance and application of the powder diffraction method in the study of polymorphism of organic mol­ecular materials.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270113017423/cu3028sup1.cif
Contains datablocks global, 3

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108270113017423/cu30283sup2.rtv
Contains datablock 3

CCDC reference: 963384

Introduction top

2-Amino­pyridine, (1) (see Scheme 1), is an effective supra­molecular reagent that readily cocrystallizes with a number of organic compounds containing at least one carb­oxy­lic acid group (Bis & Zaworotko, 2005; Bis et al., 2006). During cocrystallization, 2-amino­pyridine (pKa = 6.67) may remove the H atom from the carb­oxy­lic acid, resulting in an organic salt instead of in a cocrystal. Among these cocrystals or salts, a 2-amino­pyridine–carb­oxy­lic acid supra­molecular heterosynthon (see Scheme 1) is frequently observed (Shan et al., 2002). A search of the Cambridge Structural Database (CSD, Version 5.34; Allen, 2002) for organic compounds including only the elements C, H, O and N was conducted, and revealed 39 crystal structures containing both 2-amino­pyridine and carb­oxy­lic acid, with such a supra­molecular heterosynthon observed in all of them. Among the 48 [39 in previous sentence? Please clarify] crystal structures, the carb­oxy­lic acids form salts with 2-amino­pyridine, with the exception of 4-nitro­phthalic acid (Karmakar et al., 2008). In the case of cocrystallization of 2-amino­pyridine with fumaric acid, (2) (see Scheme 1, pKa = 3.02), the organic salt (form I) bis­(2-amino­pyridinium) fumarate–fumaric acid (1/1), (3), was reported (Ballabh et al., 2002; Büyükgüngör et al., 2004). This organic salt crystallizes in the space group P21/c, with one 2-amino­pyridinium cation, half of the fumaric acid molecule and half of the fumarate dianion in the asymmetric unit.

Fumaric acid in neutral and/or ionic forms is frequently observed when it cocrystallizes with other small organic compounds. A search of the CSD for fumaric acid in neutral or ionized forms, including only the elements C, N, O and H, revealed a total of 152 crystal structures, of which four contain fumaric acid in both neutral and monoanionic forms and 16 contain fumaric acid in both the neutral and dianionic forms. In the remaining 132 structures, the neutral form occurs in 58, the monoanionic form in 43 and the dianionic form in 31 structures. A further investigation of the crystal structures containing fumaric acid in the dianionic form showed that the fumarate dianions lie on a centre of inversion, with four exceptions [CSD refcodes COCPEQ (Reference?), HUSTIY (Reference?), VEVSAR (Reference?) and XELJED (Reference?)]. In the present work, a new polymorph of (3), viz. form II, was obtained and its crystal structure determined by powder X-ray diffraction.

Synthesis and crystallization top

Form II of (3) was obtained by dissolving 2-amino­pyridine (0.470 g, 5.00 mmol) and fumaric acid (0.580 g, 5.00 mmol) in methanol (50 ml) and heating at 353 K for 10 min. A white crystalline powder was obtained after cooling and crystallization over a period of 5 h at ambient temperature.

The ionic form of the title solvated salt, due to proton transfer from fumaric acid to the aromatic N atom of the 2-amino­pyrdine molecule, was confirmed by FT–IR characterization. Two reasonably strong bands at 1634 and 1576 cm-1 were assigned to the asymmetric stretching of the –COO- anionic group. The strongest band at 1671 cm-1 is consistent with CO stretching of the free –COOH group involved in unsaturated hydrogen bonding.

For measurement of the powder X-ray diffraction pattern, the sample was finely ground and loaded into a borosilicate capillary (0.7 mm diameter). It was spun during data collection to improve powder averaging. The powder X-ray diffraction pattern was recorded at ambient temperature in transmission mode on a Rigaku SmartLab diffractometer (9 kW rotating anode, Cu Kα1, Ge monochromated; D/teX Ultra one-dimensional detector; counting rate 0.2° min-1; 2θ range 5–70°; collection time 6 h).

Refinement top

The powder pattern was indexed using the program X-CELL (Neumann, 2003), giving a unit cell with triclinic symmetry [a = 13.36, b = 9.60 and c = 3.82 Å; α = 91.71, β = 91.74 and γ = 94.30°; FOM = 3.79 × 103). This unit cell was transformed to the following unit cell in the standard setting: a = 3.82, b = 9.60 and c = 13.36 Å; α = 94.30, β = 91.74 and γ = 91.71°. A good quality Le Bail fit (Le Bail et al., 1988), using the GSAS program package (Larson & Von Dreele, 2004) inter­faced by EXPGUI (Toby, 2001), was obtained using this unit cell, thus confirming the correctness of the unit cell. Density considerations suggest that there are two 2-amino­pyridine molecules and two fumaric acid molecules in the unit cell. An initial attempt at structure solution using the simulated annealing method implemented in Materials Studio software (Accelrys, 2011) with the space group P1 (one 2-amino­pyridine and one fumaric acid molecule in the asymmetric unit) was not successful. The structure solution was then carried out in the space group P1 (two 2-amino­pyridine molecules and two fumaric acid molecules in the asymmetric unit), leading to a reasonable crystal structure with no short contacts except for hydrogen bonds. However, a close inspection of the obtained crystal structure in the space group P1 suggested two adjacent 2-amino­pyridine molecules are approximately related by an inversion centre. Therefore, the structure solution was finally carried out in the space group P1 with one 2-amino­pyridine molecule and two halves of a fumaric acid molecule in the asymmetric unit. The 2-amino­pyridine molecule and the two halves of the fumaric acid molecule were treated as motion groups without inter­nal torsional degrees of freedom. The positions and orientations of the motion groups were varied and therefore a total of 18 variables were optimized during the structure search.

A reasonable crystal structure solution (Rwp = 5.22% and Rp = 3.58%) was obtained after two cycles of 150000 simulated annealing steps and this was taken as the initial structural model for Rietveld refinement using GSAS. In the Rietveld refinement, standard restraints were applied to bond lengths and angles, and planar restraints were applied to the 2-amino­pyridine and fumaric acid molecules. These restraints were gradually released towards the end of the Rietveld refinement. Isotropic displacement parameters were refined independently for each molecule. In the final stage of the Rietveld refinement, H atoms were introduced from geometric arguments (C—H = 0.95 Å, O—H = 0.90 Å and N—H = 0.90 Å) using the CRYSTALS program package (Betteridge et al., 2003), with a fixed isotropic displacement parameter (0.05 Å2). The fumaric acid molecule, which forms an approximately inter­molecular planar hydrogen-bonded trimer with two neighbouring 2-amino­pyridine molecules via dimeric N—H···O hydrogen bonds, was deprotonated and therefore the dianion model was employed for the Rietveld refinement. The other fumaric acid molecule, linking adjacent hydrogen-bonded trimers via a single N—H···O hydrogen bond, was treated as a free fumaric acid molecule for the Rietveld refinement. The following parameters were refined: scale factor, lattice parameters, 2θ zero error, peak profile parameters, atomic coordinates and isotropic displacement parameters. The standard uncertainties of the atomic coordinates were corrected using the procedure described by Scott (1983). The final Rietveld refinement leads to a good quality of fit (Fig. 6). The discrepancies between the experimental and calculated powder X-ray diffraction pattern in the final Rietveld refinement are comparable with those of the Le Bail fit, confirming the completeness of the structure refinement.

Results and discussion top

A view of form II of (3) with the atom-labelling scheme is shown in Fig. 1. In the crystal structure, both the fumaric acid molecule and the fumarate dianion lie on inversion centres. The fumarate dianion is involved in dimeric hydrogen-bonding inter­actions with two neighbouring 2-amino­pyridinium cations via independent N1—H6···O1 and N2—H8···O2 hydrogen bonding, resulting in an approximately inter­molecular planar hydrogen-bonded trimer, outlined by a re­cta­ngle in Fig. 2. The inter­linking between adjacent hydrogen-bonded trimers is achieved through inversion-related dimeric N2—H6···O2 hydrogen-bonding inter­actions. The extension of these two types of dimeric N—H···O hydrogen-bonding inter­action link the 2-amino­pyrdium cations and fumarate dianions into a ribbon-like packing motif. These motifs are parallel to each other and present shifted ππ stacking inter­actions, with an inter­planar distance of 3.434 (3) Å along the c axis. The free fumaric acid molecule provides a further hydrogen-bonding inter­action (O3—H10···O1) to link the ribbon-like packing motifs into the three-dimensional crystal structure of form II, shown in Fig. 3.

In form I, both the fumaric acid molecule and the fumarate dianion lie on inversion centres. As shown in Fig. 4, the fumarate dianion is linked to two neighbouring 2-amino­pyridinium cations via dimeric N—H···O hydrogen bonding to form an approximately planar inter­molecular hydrogen-bonded trimer, which is similar to that in form II. Two adjacent hydrogen-bonded trimers are linked through single N—H···O hydrogen bonding. The extension of the dimeric N—H···O hydrogen bonding and single N—H···O hydrogen bonding links the hydrogen-bonded trimers into a staircase-like packing motif. There are no significant ππ stacking inter­actions between adjacent hydrogen-bonded trimers, as a consequence of the large offset. The free fumaric acid molecule in form I provides a further hydrogen-bonding inter­action, linking the motifs into the three-dimensional crystal structure of form I, shown in Fig. 5.

Related literature top

For related literature, see: Accelrys (2011); Allen (2002); Büyükgüngör et al. (2004); Ballabh et al. (2002); Betteridge et al. (2003); Bis & Zaworotko (2005); Bis et al. (2006); Karmakar et al. (2008); Larson & Von Dreele (2004); Le Bail, Duroy & Fourquet (1988); Neumann (2003); Scott (1983); Shan et al. (2002); Toby (2001).

Computing details top

Data collection: SmartLab software (Rigaku, 2013); cell refinement: GSAS (Larson & Von Dreele, 2004); data reduction: GSAS (Larson & Von Dreele, 2004); program(s) used to solve structure: Reflex implemented in Materials Studio (Accelrys, 2011); program(s) used to refine structure: GSAS (Larson & Von Dreele, 2004); molecular graphics: ORTEP-3 (Farrugia, 2012), DIAMOND (Brandenburg, 1999) and Mercury (Macrae et al., 2008); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top
[Figure 1] Fig. 1. A view of the components of (3), form II, showing the atom-labelling scheme. Asterisks indicate symmetry-equivalent atoms [Symmetry code?]. Dashed lines indicate hydrogen bonds. Displacement spheres are drawn at the 50% probability level.
[Figure 2] Fig. 2. A view of the crystal structure of (3), form II, showing the hydrogen-bonding scheme (dashed lines). One 2-aminopyridinium–fumarate hydrogen-bonded trimer is outlined with a rectangle. H atoms not involved in hydrogen bonding have been omitted for clarity. The 2-aminopyridinium cations are shown in lightest grey (green in the electronic version of the paper), fumarate dianions in medium grey (red) and free fumaric acid molecules in darkest grey (blue).
[Figure 3] Fig. 3. The crystal packing of (3), form II, viewed approximately along [010]. H atoms have been omitted for clarity. [Dashed lines indicate hydrogen bonds?] The 2-aminopyridinium–fumarate hydrogen-bonded trimers are shown in darker grey (blue in the electronic version of the paper) and the fumaric acid molecules are shown in lighter grey (red).
[Figure 4] Fig. 4. A view of the crystal structure of (3), form I, showing the hydrogen-bonding scheme (dashed lines). One 2-aminopyridinium–fumarate hydrogen-bonded trimer is outlined with a rectangle. H atoms not involved in hydrogen bonding have been omitted for clarity. The colour code is as in Fig. 2.
[Figure 5] Fig. 5. The crystal packing of (3), form I. The 2-aminopyridinium–fumarate [Text missing?]. H atoms have been omitted for clarity. The colour code is as in Fig. 3.
[Figure 6] Fig. 6. The final Rietveld refinement for (3), form II, showing the experimental powder diffraction pattern (crosses, red in the electronic version of the paper), the calculated powder pattern (solid line, green) and the difference between the experimental and calculated powder patterns (lower line). Tick marks indicate the reflection positions. The hump is due to the borosilicate capillary. The high-angle area of the Rietveld refinement is magnified by a factor of 10.
Bis(2-aminopyridinium) fumarate–fumaric acid (1/1) top
Crystal data top
2C5H7N2+·C4H2O42·C4H4O4Z = 1
Mr = 420.38F(000) = 220
Triclinic, P1triclinic
Hall symbol: -P 1Dx = 1.432 Mg m3
a = 3.81686 (7) ÅMelting point: 463 K
b = 9.6064 (3) ÅCu Kα1 radiation, λ = 1.54056 Å
c = 13.3605 (4) ŵ = 0.98 mm1
α = 94.2974 (15)°T = 298 K
β = 91.7433 (14)°Particle morphology: powder
γ = 91.7169 (14)°white
V = 488.02 (3) Å3cylinder, 10 × 0.7 mm
Data collection top
Rigaku SmartLab
diffractometer
Data collection mode: transmission
Radiation source: rotating-anode X-ray tubeScan method: continuous
Ge 220 monochromator2θmin = 5.0°, 2θmax = 70.0°, 2θstep = 0.02°
Specimen mounting: borosilicate caplillary
Refinement top
Refinement on Inet56 parameters
Least-squares matrix: full77 restraints
Rp = 0.0350 constraints
Rwp = 0.046Hydrogen site location: inferred from neighbouring sites
Rexp = 0.032H-atom parameters not refined
R(F2) = 0.1101Weighting scheme based on measured s.u.'s
χ2 = 2.103(Δ/σ)max = 0.05
3251 data pointsBackground function: fixed background by interpolation
Excluded region(s): nonePreferred orientation correction: none
Profile function: Thompson–Cox–Hastings pseudo-Voigt
Crystal data top
2C5H7N2+·C4H2O42·C4H4O4γ = 91.7169 (14)°
Mr = 420.38V = 488.02 (3) Å3
Triclinic, P1Z = 1
a = 3.81686 (7) ÅCu Kα1 radiation, λ = 1.54056 Å
b = 9.6064 (3) ŵ = 0.98 mm1
c = 13.3605 (4) ÅT = 298 K
α = 94.2974 (15)°cylinder, 10 × 0.7 mm
β = 91.7433 (14)°
Data collection top
Rigaku SmartLab
diffractometer
Scan method: continuous
Specimen mounting: borosilicate caplillary2θmin = 5.0°, 2θmax = 70.0°, 2θstep = 0.02°
Data collection mode: transmission
Refinement top
Rp = 0.0353251 data points
Rwp = 0.04656 parameters
Rexp = 0.03277 restraints
R(F2) = 0.1101H-atom parameters not refined
χ2 = 2.103
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
C10.4140 (9)0.0637 (3)0.3110 (2)0.0574 (17)*
C20.5022 (12)0.1952 (3)0.2710 (3)0.0574 (17)*
C30.6521 (10)0.2062 (3)0.1775 (2)0.0574 (17)*
C40.7108 (13)0.0868 (3)0.1264 (3)0.0574 (17)*
C50.6188 (9)0.0404 (3)0.1718 (2)0.0574 (17)*
N10.4726 (8)0.0531 (3)0.2622 (2)0.0574 (17)*
N20.2559 (11)0.0328 (3)0.4011 (2)0.0574 (17)*
C60.0550 (12)0.4783 (3)0.4548 (2)0.0573 (18)*
C70.1394 (12)0.3332 (4)0.4281 (3)0.0573 (18)*
O10.2607 (13)0.3020 (5)0.3440 (3)0.0573 (18)*
O20.1002 (14)0.2366 (5)0.4878 (4)0.0573 (18)*
C80.0728 (12)0.5194 (3)0.0445 (2)0.0446 (15)*
C90.1499 (11)0.4202 (4)0.1185 (2)0.0446 (15)*
O30.2628 (11)0.4739 (3)0.2093 (3)0.0446 (15)*
O40.1169 (14)0.2934 (5)0.1027 (3)0.0446 (15)*
H10.093850.545970.407860.05*
H20.459820.27530.30650.05*
H30.713970.294910.148420.05*
H40.813530.092420.062450.05*
H50.657750.122020.137120.05*
H60.412780.137120.289490.05*
H70.206810.101250.441330.05*
H80.212410.056130.421160.05*
H90.100180.616460.063490.05*
H100.307170.404020.248510.05*
Geometric parameters (Å, º) top
C1—C21.389 (3)N2—H70.8988
C1—N11.355 (3)N2—H80.8980
C1—N21.380 (3)C6—C6i1.332 (6)
C2—C31.387 (3)C6—C71.461 (3)
C2—H20.9466C6—H10.9481
C3—C41.394 (3)O1—C71.247 (4)
C3—H30.9489O2—C71.277 (4)
C4—C51.383 (3)C8—C8ii1.321 (6)
C4—H40.9491C8—C91.452 (3)
C5—H50.9503C8—H90.9500
N1—C11.355 (3)O3—C91.336 (3)
N1—C51.346 (3)O3—H100.8986
N1—H60.8991O4—C91.223 (4)
C2—C1—N1122.2 (2)C5—N1—H6120.73
C2—C1—N2126.6 (2)C1—N2—H7119.95
N1—C1—N2111.1 (2)C1—N2—H8120.11
C1—C2—C3118.4 (2)H7—N2—H8119.87
C1—C2—H2120.74C6i—C6—C7122.6 (3)
C3—C2—H2120.86C6i—C6—H1118.1
C2—C3—C4119.8 (2)C7—C6—H1119.18
C2—C3—H3120.04C6—C7—O1118.9 (3)
C4—C3—H3120.12C6—C7—O2122.9 (3)
C3—C4—C5118.2 (2)O1—C7—O2118.2 (3)
C3—C4—H4120.98C8ii—C8—C9122.4 (3)
C5—C4—H4120.80C8ii—C8—H9118.1
C4—C5—N1122.8 (2)C9—C8—H9119.01
C4—C5—H5118.52C8—C9—O3116.6 (2)
N1—C5—H5118.71C8—C9—O4124.4 (3)
C1—N1—C5118.6 (2)O3—C9—O4119.1 (3)
C1—N1—H6120.71C9—O3—H10109.29
Symmetry codes: (i) x, y+1, z+1; (ii) x, y+1, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H6···O10.901.8122.710 (5)176.0
N2—H8···O20.901.9542.842 (5)170.0
N2—H7···O2iii0.902.0302.877 (6)156.7
O3—H10···O10.901.6762.532 (5)157.9
Symmetry code: (iii) x, y, z+1.

Experimental details

Crystal data
Chemical formula2C5H7N2+·C4H2O42·C4H4O4
Mr420.38
Crystal system, space groupTriclinic, P1
Temperature (K)298
a, b, c (Å)3.81686 (7), 9.6064 (3), 13.3605 (4)
α, β, γ (°)94.2974 (15), 91.7433 (14), 91.7169 (14)
V3)488.02 (3)
Z1
Radiation typeCu Kα1, λ = 1.54056 Å
µ (mm1)0.98
Specimen shape, size (mm)Cylinder, 10 × 0.7
Data collection
DiffractometerRigaku SmartLab
diffractometer
Specimen mountingBorosilicate caplillary
Data collection modeTransmission
Scan methodContinuous
2θ values (°)2θmin = 5.0 2θmax = 70.0 2θstep = 0.02
Refinement
R factors and goodness of fitRp = 0.035, Rwp = 0.046, Rexp = 0.032, R(F2) = 0.1101, χ2 = 2.103
No. of data points3251
No. of parameters56
No. of restraints77
H-atom treatmentH-atom parameters not refined

Computer programs: SmartLab software (Rigaku, 2013), GSAS (Larson & Von Dreele, 2004), Reflex implemented in Materials Studio (Accelrys, 2011), ORTEP-3 (Farrugia, 2012), DIAMOND (Brandenburg, 1999) and Mercury (Macrae et al., 2008), publCIF (Westrip, 2010).

Selected geometric parameters (Å, º) top
C1—C21.389 (3)C6—C6i1.332 (6)
C1—N21.380 (3)O1—C71.247 (4)
C3—C41.394 (3)C8—C8ii1.321 (6)
C4—C51.383 (3)O3—C91.336 (3)
N1—C11.355 (3)O4—C91.223 (4)
C2—C1—N1122.2 (2)C1—N1—C5118.6 (2)
C2—C1—N2126.6 (2)C6i—C6—C7122.6 (3)
C1—C2—C3118.4 (2)O1—C7—O2118.2 (3)
C2—C3—C4119.8 (2)C8—C9—O4124.4 (3)
C4—C5—N1122.8 (2)O3—C9—O4119.1 (3)
Symmetry codes: (i) x, y+1, z+1; (ii) x, y+1, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H6···O10.901.8122.710 (5)176.0
N2—H8···O20.901.9542.842 (5)170.0
N2—H7···O2iii0.902.0302.877 (6)156.7
O3—H10···O10.901.6762.532 (5)157.9
Symmetry code: (iii) x, y, z+1.
 

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