Bis(2-aminopyridinium) maleate

Two cyclic eight-membered hydrogen-bonded rings exist in the title compound, 2C₅H₇N₂⁺·C₄H₂O₄²⁻, involving the 2-amino­pyridinium and maleate ions. The dihedral angle between the two pyridinium rings hydrogen bonded to the maleate ion is 74.80 (4)°. The maleate anion lies on a twofold axis and is linked to the pyridinium cations by intermolecular N—H...O hydrogen bonds. The heterocycle is fully proton­ated, which enables amino–imino tautomerization.

S1. Comment

The present work is part of a structural study of complexes of 2-aminopyridinium systems with hydrogen-bond donors, and we report here the structure of bis(2-aminopyridinium) maleate, (I). A similar series of complexes formed from 2-aminopyridine and carboxylate have been reported recently (Büyükgüngör & Odabaşoǧlu, 2002; Odabaşoǧlu et al., 2003). \sch

A view of hydrogen-bonded (I) is shown in Fig. 1. The complex owes its formation to two hydrogen-bond pairs, one between atoms O1 and O2 of the maleate ions and hydrogen-bond donors N1—H1 and N2—H2A, and the other between their symmetry-related pairs. There are two eight-membered rings in the structure, formed as a result of these N—H···O hydrogen-bonds. Furthermore, there is also an intermolecular hydrogen-bond in (I) (Table 2).

The average C—O distances of carboxylate groups that form intermolecular hydrogen bonds are 1.32 (2) Å for the hydroxyl C—OH and 1.21 (3) Å for the carbonyl C═O bond (Borthwick, 1980). This value for the carboxylate anion is also reported as 1.25 Å (Borthwick, 1980). The bond lengths of O1—C11 and O2—C11 in (I) thus fall into the category of a normal COO⁻ group (Table 1).

The C—N—C angle of pyridines is very sensitive to protonation (Jin, Pan, Xu & Xu, 2000 Is this the correct citation?; Jin et al., 2002). In comparison with 2-amino-6-methylpyridinium neoabietate (Jin, Pan, Liu & Xu, 2000), the complete protonation of the heterocycle in (I) is indicated by the enlarged C1—N1—C5 angle [122.69 (15)°] and by the reduced N1—C1—C2 angle [117.47 (16)°]. The 2-aminopyridine-carboxylic acid system has been the subject of theoretical (Inuzuka & Fujimoto, 1990) and spectroscopic (Inuzuka & Fujimoto, 1986) amino-imino tautomerization studies. The main features of amino-imino tautomerization (Scheme 2) are shown in the structure of (I) by the bond lengths and angles of the heterocycle and the maleate anion, respectively. The present investigation, like our previous work (Büyükgüngör & Odabaşoǧlu, 2002; Odabaşoǧlu et al., 2003), clearly shows that the positive charge in the 2-aminopyridinium ions of (I) is on the amino group.

S2. Experimental

The title compound was prepared by dissolving 2-aminopyridine and maleic acid in a 2:1 molar ratio in water at 373 K, and crystals of (I) were obtained by slow evaporation of the solvent at the room temperature.

S3. Refinement

Although space group Cc gave a chemically reasonable and computationally stable refinement, the correct space group was found to be Fdd2. Refinement of the absolute structure parameter was meaningless because of its large s.u. (1.2), and so Friedel-pair reflections were averaged before the final refinement. All the H atoms were treated using a riding model, with C—H distances of 0.95 Å and N—H distances of 0.88 Å, and with U_iso(H) = 1.2U_eq(parent).

Computing details

Data collection: XSCANS (Siemens 1991); cell refinement: XSCANS; data reduction: SHELXTL (Sheldrick, 1990); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1998).

Figures

	Fig. 1. A view of the moieties of (I), with the atom-numbering scheme and 50% probability displacement ellipsoids [symmetry code: (i) 1/2 − x, 1/2 − y, z].
	Fig. 2. A packing diagram for (I), viewed along the c axis.

Bis(2-aminopyridinium) maleate

Crystal data

2C5H7N2^+·C4H2O4^2^−	Dx = 1.403 Mg m^−3
Mr = 304.30	Melting point = 415–418 K
Orthorhombic, Fdd2	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: F 2 -2d	Cell parameters from 161 reflections
a = 21.756 (5) Å	θ = 2.6–12.7°
b = 23.531 (5) Å	µ = 0.11 mm^−1
c = 5.6280 (11) Å	T = 153 K
V = 2881.2 (11) Å^3	Rectangular, light yellow
Z = 8	0.20 × 0.15 × 0.10 mm
F(000) = 1280

Data collection

Siemens P4 diffractometer	Rint = 0.016
Radiation source: fine-focus sealed tube	θmax = 27.0°, θmin = 2.5°
Graphite monochromator	h = −27→5
ω scans	k = −30→0
1564 measured reflections	l = −6→7
873 independent reflections	1 standard reflections every 120 min
814 reflections with I > 2σ(I)	intensity decay: <2%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.026	H-atom parameters constrained
wR(F^2) = 0.072	w = 1/[σ^2(Fo^2) + (0.0451P)^2 + 0.5722P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max < 0.001
873 reflections	Δρmax = 0.11 e Å^−3
101 parameters	Δρmin = −0.11 e Å^−3
1 restraint	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0048 (6)

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
N1	0.20760 (6)	0.10405 (5)	0.4447 (3)	0.0369 (3)
H1	0.2184	0.1279	0.5576	0.044*
N2	0.10908 (7)	0.10719 (7)	0.5886 (3)	0.0537 (4)
H2A	0.1212	0.1316	0.6973	0.064*
H2B	0.0704	0.0963	0.5835	0.064*
C1	0.14878 (7)	0.08687 (6)	0.4336 (3)	0.0378 (4)
C2	0.13296 (8)	0.04786 (8)	0.2529 (4)	0.0462 (4)
H2	0.0921	0.0340	0.2423	0.055*
C3	0.17568 (9)	0.03024 (8)	0.0951 (4)	0.0501 (5)
H3	0.1644	0.0047	−0.0281	0.060*
C4	0.23675 (9)	0.04951 (7)	0.1121 (4)	0.0495 (4)
H4	0.2671	0.0372	0.0024	0.059*
C5	0.25099 (8)	0.08613 (7)	0.2892 (4)	0.0421 (4)
H5	0.2920	0.0995	0.3047	0.051*
O1	0.23854 (5)	0.18379 (5)	0.7565 (2)	0.0413 (3)
O2	0.14697 (6)	0.18946 (6)	0.9268 (3)	0.0608 (4)
C11	0.20258 (7)	0.19907 (6)	0.9210 (3)	0.0354 (3)
C12	0.22988 (7)	0.22893 (6)	1.1315 (3)	0.0355 (3)
H12	0.2167	0.2160	1.2830	0.043*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0367 (7)	0.0372 (6)	0.0367 (7)	−0.0039 (5)	0.0012 (6)	−0.0028 (6)
N2	0.0367 (7)	0.0697 (10)	0.0547 (10)	−0.0103 (7)	0.0071 (7)	−0.0200 (8)
C1	0.0359 (7)	0.0393 (7)	0.0381 (9)	−0.0021 (6)	−0.0011 (7)	0.0018 (7)
C2	0.0414 (9)	0.0490 (9)	0.0483 (10)	−0.0053 (7)	−0.0065 (8)	−0.0074 (8)
C3	0.0594 (11)	0.0470 (9)	0.0438 (10)	0.0010 (8)	−0.0061 (9)	−0.0102 (8)
C4	0.0523 (10)	0.0504 (9)	0.0458 (10)	0.0050 (8)	0.0103 (9)	−0.0047 (9)
C5	0.0376 (8)	0.0420 (8)	0.0467 (9)	−0.0013 (6)	0.0056 (7)	0.0027 (7)
O1	0.0346 (5)	0.0495 (6)	0.0398 (6)	−0.0036 (5)	0.0037 (5)	−0.0124 (6)
O2	0.0356 (6)	0.0793 (9)	0.0675 (9)	−0.0087 (6)	0.0103 (6)	−0.0273 (8)
C11	0.0335 (7)	0.0336 (7)	0.0392 (8)	0.0001 (6)	0.0041 (7)	−0.0021 (6)
C12	0.0426 (8)	0.0348 (6)	0.0291 (7)	0.0038 (6)	0.0032 (7)	0.0015 (7)

Geometric parameters (Å, º)

N1—C1	1.3434 (19)	C3—H3	0.9500
N1—C5	1.354 (2)	C4—C5	1.354 (3)
N1—H1	0.8800	C4—H4	0.9500
N2—C1	1.318 (2)	C5—H5	0.9500
N2—H2A	0.8800	O1—C11	1.264 (2)
N2—H2B	0.8800	O2—C11	1.2310 (19)
C1—C2	1.412 (3)	C11—C12	1.500 (2)
C2—C3	1.351 (3)	C12—C12^i	1.323 (3)
C2—H2	0.9500	C12—H12	0.9500
C3—C4	1.407 (3)
C1—N1—C5	122.69 (15)	C4—C3—H3	119.8
C1—N1—H1	118.7	C5—C4—C3	118.12 (17)
C5—N1—H1	118.7	C5—C4—H4	120.9
C1—N2—H2A	120.0	C3—C4—H4	120.9
C1—N2—H2B	120.0	C4—C5—N1	120.96 (16)
H2A—N2—H2B	120.0	C4—C5—H5	119.5
N2—C1—N1	118.97 (16)	N1—C5—H5	119.5
N2—C1—C2	123.56 (15)	O2—C11—O1	125.12 (16)
N1—C1—C2	117.47 (16)	O2—C11—C12	117.01 (15)
C3—C2—C1	120.34 (16)	O1—C11—C12	117.81 (13)
C3—C2—H2	119.8	C12^i—C12—C11	127.83 (8)
C1—C2—H2	119.8	C12^i—C12—H12	116.1
C2—C3—C4	120.40 (17)	C11—C12—H12	116.1
C2—C3—H3	119.8
C5—N1—C1—N2	−178.63 (16)	C2—C3—C4—C5	−0.4 (3)
C5—N1—C1—C2	1.0 (3)	C3—C4—C5—N1	−0.5 (3)
N2—C1—C2—C3	177.82 (18)	C1—N1—C5—C4	0.1 (3)
N1—C1—C2—C3	−1.8 (3)	O2—C11—C12—C12^i	−136.4 (2)
C1—C2—C3—C4	1.5 (3)	O1—C11—C12—C12^i	46.3 (3)

Symmetry code: (i) −x+1/2, −y+1/2, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1	0.88	1.78	2.6557 (18)	172
N2—H2A···O2	0.88	1.96	2.837 (2)	177
N2—H2B···O1^ii	0.88	1.97	2.832 (2)	168

Symmetry code: (ii) x−1/4, −y+1/4, z−1/4.