2-Amino-5-methyl­pyridinium 6-oxo-1,6-dihydro­pyridine-2-carboxyl­ate

Thanigaimani, K.; Farhadikoutenaei, A.; Khalib, N.C.; Arshad, S.; Razak, I.A.

doi:10.1107/S1600536812041359

organic compounds

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ISSN: 2056-9890

Volume 68| Part 11| November 2012| Pages o3151-o3152

doi:10.1107/S1600536812041359

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2-Amino-5-methylpyridinium 6-oxo-1,6-dihydropyridine-2-carboxylate

Kaliyaperumal Thanigaimani,^a Abbas Farhadikoutenaei,^a Nuridayanti Che Khalib,^a Suhana Arshad ^a and Ibrahim Abdul Razak ^a ^*‡

^aSchool of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
^*Correspondence e-mail: arazaki@usm.my

(Received 19 September 2012; accepted 2 October 2012; online 20 October 2012)

The anion of the title salt, C₆H₉N₂⁺·C₆H₄NO₃⁻, undergoes an enol-to-keto tautomerism during the crystallization. In the crystal structure, the cation and anion are held together by a relatively short N—H⋯O hydrogen bond, and the two anions are further connected to each other by a pair of N—H⋯O hydrogen bonds with an R₂²(8) ring motif, thus forming a centrosymmetric 2 + 2 aggregate. The aggregates are further linked through weak N—H⋯O and C—H⋯O hydrogen bonds, resulting a three-dimensional network.

Related literature

For details of 2-aminopyridine and its derivatives, see: Banerjee & Murugavel (2004 ); Bis & Zaworotko (2005 ); Bis et al. (2006 ). For details of 6-hydroxypicolinic acid, see: Sun et al. (2004 ); Soares-Santos et al. (2003 ). For a related structure, see: Sawada & Ohashi (1998 ). For hydrogen-bond motifs, see: Bernstein et al. (1995 ). For bond-length data, see: Allen et al. (1987 ). For stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986 ).

Experimental

Crystal data

C₆H₉N₂⁺·C₆H₄NO₃⁻
M_r = 247.25
Monoclinic, P 2₁ /c
a = 11.7093 (6) Å
b = 10.4594 (6) Å
c = 11.4590 (6) Å
β = 119.203 (1)°
V = 1225.03 (11) Å³
Z = 4
Mo Kα radiation
μ = 0.10 mm⁻¹
T = 100 K
0.45 × 0.35 × 0.23 mm

Data collection

Bruker SMART APEXII DUO CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2009 ) T_min = 0.957, T_max = 0.978
15984 measured reflections
4430 independent reflections
3745 reflections with I > 2σ(I)
R_int = 0.027

Refinement

R[F² > 2σ(F²)] = 0.039
wR(F²) = 0.116
S = 1.02
4430 reflections
180 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.43 e Å⁻³
Δρ_min = −0.21 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1N1⋯O1ⁱ	0.899 (15)	2.011 (15)	2.8922 (10)	166.0 (16)
N3—H2N3⋯O1	0.900 (16)	2.245 (19)	3.0373 (12)	146.7 (15)
N3—H2N3⋯O3ⁱ	0.900 (16)	2.408 (16)	3.0916 (11)	133.0 (15)
N3—H1N3⋯O2ⁱⁱ	0.938 (15)	1.884 (16)	2.8071 (12)	167.7 (15)
N2—H1N2⋯O3ⁱ	0.954 (16)	1.686 (18)	2.6206 (11)	165.7 (17)
C3—H3A⋯O1ⁱⁱⁱ	0.95	2.33	3.2598 (11)	166
C9—H9A⋯O1^iv	0.95	2.54	3.3750 (12)	146
Symmetry codes: (i) -x+1, -y+1, -z+1; (ii) $[-x+1, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (iii) $[x, -y+{\script{3\over 2}}, z-{\script{1\over 2}}]$ ; (iv) $[-x, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ .

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536812041359/is5197sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536812041359/is5197Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536812041359/is5197Isup3.cml

checkCIF report

Comment top

2-Aminopyridine and its derivatives are some of the most frequently used synthons in supramolecular chemistry based on hydrogen bonds (Banerjee & Murugavel, 2004; Bis & Zaworotko, 2005; Bis et al., 2006). 6-Hydroxypicolinic acid has interesting characteristics: firstly, it was characterized by a similar enol-keto tautomerism due to the labile hydrogen atom of –OH group in α-position migrating easily to the basic pyridine N atom; secondly, the multiple coordination sites such as the carbonyl oxygen, the amide nitrogen and carboxylate oxygen atoms are able to coordinate with various metal ions (Sun et al., 2004; Soares-Santos et al., 2003). In order to study some interesting hydrogen bonding interactions of this compound, the synthesis and structure of the title salt is presented here.

The asymmetric unit of the title compound contains a 2-amino-5-methylpyridinium cation and a 6-oxo-1,6-dihydropyridine-2-carboxylate anion (Fig. 1). The 2-amino-5-methylpyridinium cation is planar, with a maximum deviation of 0.004 (1) Å for atoms N2 and C9. In the cation, a wider than normal angle [C11—N2—C12 = 122.96 (8)°] is subtended at the protonated N2 atom. The bond lengths (Allen et al., 1987) and angles are normal. The anion exists in the keto-enol tautomerism of the –CONH moiety. Similar form was also observed in the crystal structure of 2-oxo-1,2-dihydropyridine-6-carboxylic acid (Sawada & Ohashi, 1998).

In the crystal (Fig. 2), the 6-oxo-1,6-dihydropyridine-2-carboxylate anion are centrosymmetrically paired through a pair of N1—H1N1···O1ⁱ hydrogen bonds (symmetry code in Table 1) to form an R₂²(8) (Bernstein et al., 1995) ring motif. These motifs are further self-organized through N—H···O hydrogen bonds to generate an array of four hydrogen bonds, resulting in the rings with R₂²(8), sandwiched by two R₂²(7). One of the O atoms of the carboxylate group acts as an acceptors of bifurcated N2—H1N2···O3ⁱ and N3—H2N3···O3ⁱ hydrogen bonds (symmetry code in Table 1) with the protonated pyridine and amine N atoms of the cation, forming an R₂¹(6) ring motif. The crystal structure are further stabilized by strong N3—H1N3···O2ⁱⁱ and weak C3—H3A···O1ⁱⁱⁱ and C9—H9A···O1^iv hydrogen bonds (symmetry codes in Table 1), resulting a three-dimensional network.

Related literature top

For details of 2-aminopyridine and its derivatives, see: Banerjee & Murugavel (2004); Bis & Zaworotko (2005); Bis et al. (2006). For details of 6-hydroxypicolinic acid, see: Sun et al. (2004); Soares-Santos et al. (2003). For a related structure, see: Sawada & Ohashi (1998). For hydrogen-bond motifs, see: Bernstein et al. (1995). For bond-length data, see: Allen et al. (1987). For stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986).

Experimental top

Hot methanol solutions (20 ml) of 2-amino5-methylpyridine (54 mg, Aldrich) and 6-Hydroxypicolinic acid (69 mg, Merck) were mixed and warmed over a heating magnetic stirrer hotplate for a few minutes. The resulting solution was allowed to cool slowly at room temperature and crystals of the title compound (I) appeared after a few days.

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures top

	Fig. 1. The molecular structure of the title compound with atom labels with 50% probability displacement ellipsoids.
	Fig. 2. The crystal packing of the title compound, viewed down the c axis.

2-Amino-5-methylpyridinium 6-oxo-1,6-dihydropyridine-2-carboxylate top

Crystal data top

C₆H₉N₂⁺·C₆H₄NO₃⁻	F(000) = 520
M_r = 247.25	D_x = 1.341 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 6176 reflections
a = 11.7093 (6) Å	θ = 3.6–32.6°
b = 10.4594 (6) Å	µ = 0.10 mm⁻¹
c = 11.4590 (6) Å	T = 100 K
β = 119.203 (1)°	Block, colourless
V = 1225.03 (11) Å³	0.45 × 0.35 × 0.23 mm
Z = 4

Data collection top

Bruker SMART APEXII DUO CCD area-detector diffractometer	4430 independent reflections
Radiation source: fine-focus sealed tube	3745 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.027
ϕ and ω scans	θ_max = 32.6°, θ_min = 3.6°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −17→17
T_min = 0.957, T_max = 0.978	k = −15→15
15984 measured reflections	l = −16→17

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.039	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.116	H atoms treated by a mixture of independent and constrained refinement
S = 1.02	w = 1/[σ²(F_o²) + (0.0661P)² + 0.2292P] where P = (F_o² + 2F_c²)/3
4430 reflections	(Δ/σ)_max < 0.001
180 parameters	Δρ_max = 0.43 e Å⁻³
0 restraints	Δρ_min = −0.21 e Å⁻³

Crystal data top

C₆H₉N₂⁺·C₆H₄NO₃⁻	V = 1225.03 (11) Å³
M_r = 247.25	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 11.7093 (6) Å	µ = 0.10 mm⁻¹
b = 10.4594 (6) Å	T = 100 K
c = 11.4590 (6) Å	0.45 × 0.35 × 0.23 mm
β = 119.203 (1)°

Data collection top

Bruker SMART APEXII DUO CCD area-detector diffractometer	4430 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2009)	3745 reflections with I > 2σ(I)
T_min = 0.957, T_max = 0.978	R_int = 0.027
15984 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.039	0 restraints
wR(F²) = 0.116	H atoms treated by a mixture of independent and constrained refinement
S = 1.02	Δρ_max = 0.43 e Å⁻³
4430 reflections	Δρ_min = −0.21 e Å⁻³
180 parameters

Special details top

Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.

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

	x	y	z	U_iso*/U_eq
O1	0.37734 (6)	0.60282 (6)	0.39711 (6)	0.01806 (13)
O2	0.80810 (7)	0.48126 (7)	0.29773 (7)	0.02633 (15)
O3	0.79587 (6)	0.45930 (6)	0.48584 (7)	0.02282 (14)
N1	0.55569 (6)	0.55843 (7)	0.37336 (7)	0.01512 (13)
N2	0.02845 (7)	0.72276 (7)	0.43791 (7)	0.01818 (14)
N3	0.14291 (7)	0.77377 (8)	0.32695 (8)	0.02345 (16)
C1	0.43630 (7)	0.61584 (7)	0.33157 (8)	0.01518 (14)
C2	0.38707 (8)	0.68852 (8)	0.21019 (8)	0.02096 (16)
H2A	0.3064	0.7328	0.1776	0.025*
C3	0.45395 (9)	0.69519 (10)	0.14089 (9)	0.02493 (18)
H3A	0.4195	0.7439	0.0608	0.030*
C4	0.57443 (9)	0.63000 (9)	0.18740 (9)	0.02318 (17)
H4A	0.6203	0.6326	0.1382	0.028*
C5	0.62317 (8)	0.56351 (8)	0.30428 (8)	0.01706 (15)
C6	0.75338 (8)	0.49530 (8)	0.36664 (9)	0.01855 (15)
C7	−0.25015 (10)	0.86990 (10)	0.46610 (12)	0.0311 (2)
H7A	−0.2490	0.7998	0.5234	0.047*
H7B	−0.3361	0.8737	0.3856	0.047*
H7C	−0.2328	0.9509	0.5149	0.047*
C8	−0.14653 (8)	0.84727 (8)	0.42693 (9)	0.02107 (16)
C9	−0.12821 (9)	0.93128 (9)	0.34046 (10)	0.02358 (17)
H9A	−0.1834	1.0039	0.3055	0.028*
C10	−0.03306 (9)	0.91053 (9)	0.30608 (9)	0.02217 (17)
H10A	−0.0219	0.9685	0.2486	0.027*
C11	0.04861 (7)	0.80162 (8)	0.35711 (8)	0.01760 (15)
C12	−0.06528 (8)	0.74369 (8)	0.47303 (8)	0.01970 (16)
H12A	−0.0746	0.6849	0.5310	0.024*
H1N1	0.5904 (14)	0.5129 (15)	0.4496 (14)	0.033 (3)*
H2N3	0.1961 (15)	0.7063 (15)	0.3644 (15)	0.037 (4)*
H1N3	0.1663 (14)	0.8348 (15)	0.2824 (14)	0.034 (3)*
H1N2	0.0830 (15)	0.6489 (15)	0.4686 (16)	0.040 (4)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0171 (3)	0.0218 (3)	0.0192 (3)	0.0032 (2)	0.0119 (2)	0.0018 (2)
O2	0.0276 (3)	0.0276 (3)	0.0359 (4)	0.0033 (2)	0.0250 (3)	0.0001 (3)
O3	0.0197 (3)	0.0248 (3)	0.0278 (3)	0.0060 (2)	0.0146 (2)	0.0074 (2)
N1	0.0151 (3)	0.0164 (3)	0.0162 (3)	0.0019 (2)	0.0095 (2)	0.0018 (2)
N2	0.0169 (3)	0.0183 (3)	0.0205 (3)	0.0015 (2)	0.0101 (2)	0.0027 (2)
N3	0.0218 (3)	0.0263 (4)	0.0279 (4)	0.0065 (3)	0.0166 (3)	0.0067 (3)
C1	0.0146 (3)	0.0155 (3)	0.0166 (3)	0.0011 (2)	0.0084 (3)	−0.0002 (2)
C2	0.0188 (3)	0.0228 (4)	0.0218 (4)	0.0046 (3)	0.0104 (3)	0.0068 (3)
C3	0.0245 (4)	0.0297 (4)	0.0229 (4)	0.0045 (3)	0.0134 (3)	0.0097 (3)
C4	0.0245 (4)	0.0278 (4)	0.0234 (4)	0.0029 (3)	0.0165 (3)	0.0062 (3)
C5	0.0178 (3)	0.0177 (3)	0.0201 (3)	0.0008 (2)	0.0128 (3)	0.0003 (3)
C6	0.0184 (3)	0.0156 (3)	0.0269 (4)	0.0005 (2)	0.0152 (3)	0.0003 (3)
C7	0.0284 (4)	0.0308 (5)	0.0453 (6)	−0.0001 (4)	0.0269 (4)	−0.0044 (4)
C8	0.0190 (3)	0.0219 (4)	0.0259 (4)	−0.0008 (3)	0.0138 (3)	−0.0025 (3)
C9	0.0213 (4)	0.0218 (4)	0.0293 (4)	0.0058 (3)	0.0137 (3)	0.0036 (3)
C10	0.0223 (4)	0.0217 (4)	0.0246 (4)	0.0053 (3)	0.0131 (3)	0.0063 (3)
C11	0.0160 (3)	0.0194 (3)	0.0182 (3)	0.0009 (2)	0.0090 (3)	0.0009 (3)
C12	0.0195 (3)	0.0210 (4)	0.0215 (4)	−0.0020 (3)	0.0122 (3)	−0.0002 (3)

Geometric parameters (Å, º) top

O1—C1	1.2511 (9)	C3—H3A	0.9500
O2—C6	1.2447 (9)	C4—C5	1.3628 (12)
O3—C6	1.2617 (11)	C4—H4A	0.9500
N1—C5	1.3654 (9)	C5—C6	1.5104 (11)
N1—C1	1.3751 (10)	C7—C8	1.5036 (12)
N1—H1N1	0.899 (15)	C7—H7A	0.9800
N2—C11	1.3440 (11)	C7—H7B	0.9800
N2—C12	1.3585 (10)	C7—H7C	0.9800
N2—H1N2	0.954 (16)	C8—C12	1.3665 (12)
N3—C11	1.3402 (10)	C8—C9	1.4169 (13)
N3—H2N3	0.900 (16)	C9—C10	1.3681 (12)
N3—H1N3	0.938 (15)	C9—H9A	0.9500
C1—C2	1.4361 (11)	C10—C11	1.4172 (11)
C2—C3	1.3622 (12)	C10—H10A	0.9500
C2—H2A	0.9500	C12—H12A	0.9500
C3—C4	1.4161 (12)

C5—N1—C1	123.96 (7)	O2—C6—O3	126.76 (8)
C5—N1—H1N1	118.0 (9)	O2—C6—C5	117.96 (8)
C1—N1—H1N1	118.0 (9)	O3—C6—C5	115.27 (7)
C11—N2—C12	122.96 (7)	C8—C7—H7A	109.5
C11—N2—H1N2	116.1 (9)	C8—C7—H7B	109.5
C12—N2—H1N2	121.0 (9)	H7A—C7—H7B	109.5
C11—N3—H2N3	120.9 (9)	C8—C7—H7C	109.5
C11—N3—H1N3	119.2 (9)	H7A—C7—H7C	109.5
H2N3—N3—H1N3	118.4 (13)	H7B—C7—H7C	109.5
O1—C1—N1	120.55 (7)	C12—C8—C9	116.59 (8)
O1—C1—C2	124.11 (7)	C12—C8—C7	121.36 (8)
N1—C1—C2	115.33 (7)	C9—C8—C7	122.05 (8)
C3—C2—C1	121.23 (7)	C10—C9—C8	121.70 (8)
C3—C2—H2A	119.4	C10—C9—H9A	119.2
C1—C2—H2A	119.4	C8—C9—H9A	119.2
C2—C3—C4	120.43 (8)	C9—C10—C11	119.28 (8)
C2—C3—H3A	119.8	C9—C10—H10A	120.4
C4—C3—H3A	119.8	C11—C10—H10A	120.4
C5—C4—C3	118.57 (7)	N3—C11—N2	119.21 (8)
C5—C4—H4A	120.7	N3—C11—C10	122.91 (8)
C3—C4—H4A	120.7	N2—C11—C10	117.88 (7)
C4—C5—N1	120.42 (7)	N2—C12—C8	121.60 (8)
C4—C5—C6	123.23 (7)	N2—C12—H12A	119.2
N1—C5—C6	116.33 (7)	C8—C12—H12A	119.2

C5—N1—C1—O1	176.99 (7)	C4—C5—C6—O3	167.03 (9)
C5—N1—C1—C2	−2.64 (11)	N1—C5—C6—O3	−11.36 (11)
O1—C1—C2—C3	−177.60 (9)	C12—C8—C9—C10	−0.71 (14)
N1—C1—C2—C3	2.02 (12)	C7—C8—C9—C10	179.51 (9)
C1—C2—C3—C4	0.03 (15)	C8—C9—C10—C11	0.60 (14)
C2—C3—C4—C5	−1.64 (15)	C12—N2—C11—N3	−179.75 (8)
C3—C4—C5—N1	1.11 (14)	C12—N2—C11—C10	−0.56 (12)
C3—C4—C5—C6	−177.22 (8)	C9—C10—C11—N3	179.19 (9)
C1—N1—C5—C4	1.13 (13)	C9—C10—C11—N2	0.03 (13)
C1—N1—C5—C6	179.56 (7)	C11—N2—C12—C8	0.45 (13)
C4—C5—C6—O2	−12.31 (13)	C9—C8—C12—N2	0.19 (13)
N1—C5—C6—O2	169.31 (8)	C7—C8—C12—N2	179.97 (8)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N1···O1ⁱ	0.899 (15)	2.011 (15)	2.8922 (10)	166.0 (16)
N3—H2N3···O1	0.900 (16)	2.245 (19)	3.0373 (12)	146.7 (15)
N3—H2N3···O3ⁱ	0.900 (16)	2.408 (16)	3.0916 (11)	133.0 (15)
N3—H1N3···O2ⁱⁱ	0.938 (15)	1.884 (16)	2.8071 (12)	167.7 (15)
N2—H1N2···O3ⁱ	0.954 (16)	1.686 (18)	2.6206 (11)	165.7 (17)
C3—H3A···O1ⁱⁱⁱ	0.95	2.33	3.2598 (11)	166
C9—H9A···O1^iv	0.95	2.54	3.3750 (12)	146

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+1, y+1/2, −z+1/2; (iii) x, −y+3/2, z−1/2; (iv) −x, y+1/2, −z+1/2.

Experimental details

Crystal data
Chemical formula	C₆H₉N₂⁺·C₆H₄NO₃⁻
M_r	247.25
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	100
a, b, c (Å)	11.7093 (6), 10.4594 (6), 11.4590 (6)
β (°)	119.203 (1)
V (Å³)	1225.03 (11)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.10
Crystal size (mm)	0.45 × 0.35 × 0.23

Data collection
Diffractometer	Bruker SMART APEXII DUO CCD area-detector diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2009)
T_min, T_max	0.957, 0.978
No. of measured, independent and observed [I > 2σ(I)] reflections	15984, 4430, 3745
R_int	0.027
(sin θ/λ)_max (Å⁻¹)	0.759

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.039, 0.116, 1.02
No. of reflections	4430
No. of parameters	180
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.43, −0.21

Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N1···O1ⁱ	0.899 (15)	2.011 (15)	2.8922 (10)	166.0 (16)
N3—H2N3···O1	0.900 (16)	2.245 (19)	3.0373 (12)	146.7 (15)
N3—H2N3···O3ⁱ	0.900 (16)	2.408 (16)	3.0916 (11)	133.0 (15)
N3—H1N3···O2ⁱⁱ	0.938 (15)	1.884 (16)	2.8071 (12)	167.7 (15)
N2—H1N2···O3ⁱ	0.954 (16)	1.686 (18)	2.6206 (11)	165.7 (17)
C3—H3A···O1ⁱⁱⁱ	0.95	2.33	3.2598 (11)	166
C9—H9A···O1^iv	0.95	2.54	3.3750 (12)	146

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+1, y+1/2, −z+1/2; (iii) x, −y+3/2, z−1/2; (iv) −x, y+1/2, −z+1/2.

Footnotes

‡Thomson Reuters ResearcherID: A-5599-2009.

Acknowledgements

The authors thank the Malaysian Government and Universiti Sains Malaysia (USM) for research facilities and the Fundamental Research Grant Scheme (FRGS) No. 203/PFIZIK/6711171 to conduct this work. KT thanks The Academy of Sciences for the Developing World and USM for a TWAS–USM fellowship.

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