Proton sharing in bis­­(4-carbamoyl­pyridinium) squarate

Reaction in aqueous solution of nickel(II) squarate with isonicotinamide yielded well formed yellow crystals of the title compound, 2C₆H₆N₂O⁺·C₄O₄²⁻, as a side product. The squarate dianion is bisected by a crystallographic twofold rotation axis, which passes through the centres of two opposite bonds of the ring. Crystal structure analysis reveals that, far from forming discrete ionic species, it is likely that there is a large degree of proton sharing between the anion and cation, with the H atom lying almost symmetrically between the donor and acceptor sites, as evidenced by the long N—H and short H⋯O distances [1.15 (3) and 1.39 (3) Å, respectively]. Other hydrogen bonding is more conventional, and there are weaker C—H⋯O inter­actions contributing additional stability to the structure.

Comment

Squaric acid and its metal complexes have received considerable attention, not only in consideration of their coordination chemistry but also for their use in crystal engineering (Reetz et al., 1994). Complexes are known for almost all first-row transition metals, with several heavier transition metal and lanthanide complexes also reported. Deprotonation of squaric acid yields either an anion or a dianion, and these anions can behave as either mono- or polydentate ligands

towards first-row transition metal ions, as well as bridging two or more metal atoms (Bernardinelli et al., 1989; Castro et al., 1999). We have also used isonicotinamide as a second ligand. Apart from its biological importance (Ahuja & Prasad, 1976), it is also of inter­est in chemistry since the ligand has three donor sites, viz. (i) the pyridine ring N atom, (ii) the amine N atom and (iii) the carbonyl O atom. In our ongoing research on squaric acid, we have synthesized some mixed-ligand metal complexes of squaric acid and their structures have been reported (Uçar et al., 2004, 2005; Bulut et al., 2004). Whilst preparing a nickel coordination complex, crystals of diiso­nico­tinamidium squarate, (I), were formed as a side product.

Compound (I) crystallizes in space group C2/c, with the squarate dianion bisected by the crystallographic twofold rotation axis that passes through the centres of two opposite bonds of the ring (Fig. 1 and Table 1). The most noteworthy aspect of the structure of this compound is the behaviour of the H atoms in hydrogen bonding (Table 2). Hydrogen bonding from the NH₂ group is conventional (in terms of geometry), with both H atoms being donated. However, the N—H⋯O hydrogen bond linking the squarate dianion to the protonated ring N atom of the iso­nico­tinamidium cation has much more unusual behaviour. The freely refined N—H bond length is 1.15 (3) Å, very long for an N—H covalent bond, which would be expected to be around 0.85 Å in an X-ray crystallographic analysis. Consequently, the H⋯O distance is 1.39 (3) Å, which is rather short. Given that the overall N⋯O distance is relatively short at 2.5322 (16) Å, these values indicate a strong hydrogen bond, which nevertheless displays unusual disorder or thermal motion. A difference Fourier map (Fig. 2; Farrugia, 1999) of the electron density associated with this H atom shows this to be smeared out between the N and O atoms, with the maximum lying closer to the N than the O atom, rather than being bound closely to the N atom to give a discrete ion pair. This has consequences for the assignment of charges to the two species. Although formally the isonicotinamide mol­ecule has been protonated and squaric acid has been doubly deprotonated, the behaviour of the H atom concerned shows that this is not entirely the case and suggests that there is a large degree of covalency in this inter­action. The related compound dinico­tinamidium squarate (Bulut et al., 2003) has a similar short strong N—H⋯O hydrogen bond, although the N—H distance is shorter [1.08 (2) Å].

The crystal packing consists of hydrogen-bonded tapes, which are then linked to other tapes by further hydrogen bonding. As shown in Fig. 3, the tapes consist of an R₂²(8) graph-set motif (Bernstein et al., 1995) between the amide groups, which connects two isonicotinamidium ions into a dimer, with the hydrogen bond discussed above linking these dimers to the squarate dianion. This inter­action combines with a C—H⋯O inter­action to form a second, different, R₂²(8) motif. The torsion angle between the amide group and the pyridine ring, O1—C1—C2—C6, is −18.8 (2)°. This twist means that a second hydrogen bond from the amide group to a squarate dianion, which is not in the plane of the donor parent mol­ecule, links the tapes together, such that the overall packing between the tapes is `stepped' rather than forming flat sheets and generates a three-dimensional network. There is additional, weaker, C—H⋯O hydrogen bonding securing the tapes together, although it is unlikely that this has a significant structure-directing influence.

Figure 1 Twice the asymmetric unit of (I), with displacement ellipsoids at the 50% probability level. N—H⋯O inter­actions are shown as dashed lines. [Symmetry code (twofold axis): (i) −x + 1, y, −z + .]

Figure 2 A difference Fourier map of the electron density associated with the N—H⋯O inter­action between the isonicotinamidium cation and the squarate dianion. The diffuse nature of the electron density is clear, with the largest concentration of electron density located closer to the N than to the O atom.

Figure 3 A perspective view of the hydrogen bonding in (I). Dashed lines indicate N—H⋯O and C—H⋯O inter­actions. Note the twist of the amide groups forming a hydrogen bond with a squarate dianion out of the plane of the donor parent mol­ecule. [Symmetry codes: (ii) x, −y + 1, z + ; (iii) −x + , −y + , −z + 2; (iv) −x + 1, −y, −z + 1; (v) x, −y, z + .]

Experimental

Squaric acid (0.57 g, 5 mmol) dissolved in water (25 ml) was neutralized with NaOH (0.40 g, 10 mmol) and the mixture was added to a hot solution of NiCl₂·6H₂O (1.19 g, 5 mmol) in water (50 ml). The mixture was stirred at 333 K for 12 h and then cooled to room temperature. The green crystals that formed were filtered off, washed with water and ethanol, and dried in vacuo. A solution of isonicotinamide (0.24 g, 2 mmol) in methanol (50 ml) was added dropwise with stirring to a suspension of NiSq·2H₂O (0.21 g, 1 mmol) in water (50 ml). The green solution was refluxed for about 2 h and then cooled to room temperature. A few days later, green crystals of the desired Ni complex had formed, along with some well formed yellow block-shaped crystals of (I).

Crystal data

• 2C₆H₆N₂O⁺·C₄H₂O₄²⁻

• M_r = 358.32

• Monoclinic, C 2/c

• a = 11.959 (2) Å

• b = 10.691 (2) Å

• c = 12.257 (3) Å

• β = 104.93 (3)°

• V = 1514.3 (6) ų

• Z = 4

• D_x = 1.572 Mg m⁻³

• Mo Kα radiation

• Cell parameters from 4241 reflections

• θ = 2.5–27.5°

• μ = 0.12 mm⁻¹

• T = 150 (2) K

• Prism, yellow

• 0.41 × 0.29 × 0.12 mm

Data collection

• Nonius KappaCCD diffractometer

• φ and ω scans

• Absorption correction: multi-scan(SADABS; Sheldrick, 2003)T_min = 0.911, T_max = 0.985

• 10470 measured reflections

• 1731 independent reflections

• 1318 reflections with I > 2σ(I)

• R_int = 0.051

• θ_max = 27.5°

• h = −15 → 15

• k = −13 → 13

• l = −15 → 15

Refinement

• Refinement on F²

• R[F² > 2σ(F²)] = 0.039

• wR(F²) = 0.105

• S = 1.03

• 1731 reflections

• 130 parameters

• H atoms treated by a mixture of independent and constrained refinement

• w = 1/[σ²(F_o²) + (0.0522P)² + 0.9909P] where P = (F_o² + 2F_c²)/3

• (Δ/σ)_max < 0.001

• Δρ_max = 0.35 e Å⁻³

• Δρ_min = −0.24 e Å⁻³

Table 1
Selected geometric parameters (Å, °)

O1—C1	1.2383 (18)
N1—C1	1.331 (2)
C1—C2	1.518 (2)
O2—C7	1.2384 (17)
O3—C8	1.2756 (18)
C7—C7^i	1.503 (3)
C7—C8	1.461 (2)
C8—C8^i	1.436 (3)

O1—C1—C2—C3	161.17 (14)
O1—C1—C2—C6	−18.8 (2)
N1—C1—C2—C3	−18.6 (2)
N1—C1—C2—C6	161.46 (14)
Symmetry code: (i) .

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H2N⋯O2^ii	0.88 (2)	2.03 (2)	2.8940 (19)	169 (2)
N1—H1N⋯O1^iii	0.91 (2)	2.01 (2)	2.9208 (18)	172 (2)
N2—H3N⋯O3	1.15 (3)	1.39 (3)	2.5322 (16)	171 (2)
C3—H3⋯O2^ii	0.95	2.57	3.3249 (19)	137
C4—H4⋯O2	0.95	2.48	3.2909 (19)	143
C5—H5⋯O3^iv	0.95	2.51	3.1921 (19)	129
C6—H6⋯O3^v	0.95	2.54	3.339 (2)	141
Symmetry codes: (ii) ; (iii) ; (iv) -x+1, -y, -z+1; (v) .

All H atoms were located in a difference Fourier map. H atoms bound to N atoms were freely refined; the N—H distances are in the range 0.88 (2)–1.15 (3) Å. H atoms bound to C atoms were constrained to ride on their parent atom, with C—H distances of 0.95 Å and isotropic displacement parameters 1.2 times the U_eq values of the parent atoms.

Data collection: COLLECT (Nonius, 1998); cell refinement: EVALCCD (Duisenberg et al., 2003); data reduction: EVALCCD; program(s) used to solve structure: SHELXTL (Sheldrick, 2001); program(s) used to refine structure: SHELXTL; molecular graphics: DIAMOND (Brandenburg & Putz, 2004); software used to prepare material for publication: SHELXTL, WinGX (Farrugia, 1999) and local programs.

Supporting information

S1. Comment

Squaric acid and its metal complexes have received considerable attention, not only in consideration of their coordination chemistry but also for their use in crystal engineering (Reetz et al., 1994). Complexes are known for almost all first-row transition metals, with several heavier transition metal and lanthanide complexes also reported. Deprotonation of squaric acid yields either an anion or a dianion, and these anions can behave as either mono- or polydentate ligands towards first-row transition metal ions, as well as bridging two or more metal atoms (Bernardinelli et al., 1989; Castro et al., 1999). We have also used isonicotinamide as a second ligand. Apart from its biological importance (Ahuja & Prasad, 1976), it is also of interest in chemistry since the ligand has three donor sites, viz. (i) the pyridine ring N atom, (ii) the amine N atom and (iii) the carbonyl O atom. In our ongoing research on squaric acid, we have synthesized some mixed-ligand metal complexes of squaric acid and their structures have been reported (Uçar et al., 2004, 2005; Bulut et al., 2004). Whilst preparing a nickel coordination complex, crystals of diisonicotinamidium squarate, (I), were formed as a side-product.

Compound (I) crystallizes in space group C2/c, with the squarate dianion bisected by the crystallographic twofold rotation axis, which passes through the centres of two opposite bonds of the ring (Fig. 1). The most noteworthy aspect of the structure of this compound is the behaviour of the H atoms in hydrogen bonding. Hydrogen bonding from the NH₂ group is conventional (in terms of geometry), with both H atoms being donated. However, the N—H···O hydrogen bond linking the squarate dianion to the protonated ring N atom of the isonicotinamidium cation has much more unusual behaviour. The freely refined N—H bond length is 1.15 (3) Å, very long for an N—H covalent bond, which would be expected to be around 0.85 Å in an X-ray crystallographic analysis. Consequently, the H···A distance is 1.39 (3) Å, which is rather short. Given that the overall D···A distance is relatively short at 2.5322 (16) Å, this indicates a strong hydrogen bond, which nevertheless displays unusual disorder or thermal motion. A difference Fourier map (Fig. 2; Farrugia, 1999) of the electron density associated with this H atom shows this to be smeared out between the N and O atoms, with the maximum lying closer to N than O, rather than being bound closely to N to give a discrete ion pair. This fact has consequences for the assignment of charges to the two species. Although formally the isonicotinamide molecule has been protonated and squaric acid has been doubly deprotonated, the behaviour of the H atom concerned shows that this is not entirely the case and suggests that there is a large degree of covalency in this interaction. The related compound dinicotinamidium squarate (Bulut et al., 2003) has a similar short strong N—H···O hydrogen bond, although the N—H distance is shorter [1.08 (2) Å] in this instance.

The crystal packing consists of hydrogen-bonded tapes, which are then linked to other tapes by further hydrogen bonding. As shown in Fig. 3, the tapes consist of an R²₂(8) graph-set motif (Bernstein et al., 1995) between the amide groups, which connects two isonicotinamidium ions into a dimer, with the hydrogen bond discussed above linking these dimers to the squarate dianion. This interaction combines with a C—H···O interaction to form a second, different R²₂(8) motif. The torsion angle between the amide group and the pyridine ring, O1—C1—C2—C6, is −18.8 (2)°. This twist means that a second hydrogen bond from the amide group to a squarate dianion, which is not in the plane of the donor parent molecule, links the tapes together, such that the overall packing between the tapes is `stepped' rather than forming flat sheets and generates a three-dimensional network. There is additional, weaker C—H···O hydrogen bonding securing the tapes together, although it is unlikely that this has a significant structure-directing influence.

S2. Experimental

Squaric acid (0.57 g, 5 mmol) dissolved in water (25 ml) was neutralized with NaOH (0.40 g, 10 mmol) and the mixture was added to a hot solution of NiCl₂·6H₂O (1.19 g, 5 mmol) dissolved in water (50 ml). The mixture was stirred at 333 K for 12 h and then cooled to room temperature. The green crystals that formed were filtered off, washed with water and ethanol, and dried in vacuo. A solution of isonicotinamide (0.24 g, 2 mmol) in methanol (50 ml) was added dropwise with stirring to a suspension of NiSq·2H₂O (0.21 g, 1 mmol) in water (50 ml). The green solution was refluxed for about 2 h and then cooled to room temperature. A few days later, green crystals of the desired Ni complex had formed, along with some well formed yellow block crystals of diisonicotinamidium squarate, (I).

S3. Refinement

All H atoms were located in a difference Fourier map. N-bound H atoms were freely refined, with N—H distances in the range 0.88 (2)–1.15 (3) Å. C-bound H atoms were constrained to ride on the parent C atom with, U_iso(H) = 1.2 U_eq(C) and C—H = 0.95 Å.

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: EVALCCD (Duisenberg et al., 2003); data reduction: EVALCCD; program(s) used to solve structure: SHELXTL (Sheldrick, 2001); program(s) used to refine structure: SHELXTL; molecular graphics: DIAMOND (Brandenburg & Putz, 2004); software used to prepare material for publication: SHELXTL, WinGX (Farrugia, 1999) and local programs.

Figures

	Fig. 1. Twice the asymmetric unit of (I), with displacement ellipsoids at the 50% probability level. N—H.·O interactions are shown as dashed lines. [Symmetry operator (twofold axis): (i) 1 − x, y, 1/2 − z.]
	Fig. 2. A difference Fourier map of the electron density associated with the N—H···O interaction between isonicotinamidium and the squarate dianion. The diffuse nature of the electron density is clear, with the largest concentration of electron density located closer to N than to O.
	Fig. 3. A perspective view of the hydrogen bonding in (I). Dashed lines (blue in the online version) indicate N—H···O interactions and (red) C—H···O interactions. Note the twist of the amide groups forming a hydrogen bond with a squarate dianion out of the plane of the donor parent molecule. [Symmetry operators: (ii) x, 1 − y, 1/2 + z; (iii) 1/2 − x, 1/2 − y, 2 − z; (iv) 1 − x, −y, 1 − z; (v) x, −y, 1/2 + z.]

bis(4-carbamoylpyridinium) squarate

Crystal data

2C6H6N2O^+·C4H2O4^2^−	F(000) = 744
Mr = 358.32	Dx = 1.572 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 4241 reflections
a = 11.959 (2) Å	θ = 2.5–27.5°
b = 10.691 (2) Å	µ = 0.12 mm^−1
c = 12.257 (3) Å	T = 150 K
β = 104.93 (3)°	Prism, yellow
V = 1514.3 (6) Å^3	0.41 × 0.29 × 0.12 mm
Z = 4

Data collection

Nonius KappaCCD diffractometer	1731 independent reflections
Radiation source: sealed tube	1318 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.051
ϕ and ω scans	θmax = 27.5°, θmin = 3.9°
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	h = −15→15
Tmin = 0.911, Tmax = 0.985	k = −13→13
10470 measured reflections	l = −15→15

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.039	Hydrogen site location: difference Fourier map
wR(F^2) = 0.105	H atoms treated by a mixture of independent and constrained refinement
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0522P)^2 + 0.9909P] where P = (Fo^2 + 2Fc^2)/3
1731 reflections	(Δ/σ)max < 0.001
130 parameters	Δρmax = 0.35 e Å^−3
0 restraints	Δρmin = −0.24 e Å^−3

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.26278 (10)	0.13824 (10)	0.88968 (9)	0.0254 (3)
N1	0.32383 (13)	0.33974 (13)	0.90905 (11)	0.0238 (3)
H2N	0.3619 (16)	0.4002 (19)	0.8865 (15)	0.033 (5)*
H1N	0.3036 (16)	0.3464 (17)	0.9758 (17)	0.035 (5)*
N2	0.39541 (11)	0.19582 (12)	0.54097 (10)	0.0199 (3)
H3N	0.425 (2)	0.181 (2)	0.459 (2)	0.073 (8)*
C1	0.30471 (12)	0.23105 (14)	0.85451 (12)	0.0186 (3)
C2	0.33645 (12)	0.22292 (14)	0.74249 (12)	0.0172 (3)
C3	0.35248 (13)	0.32773 (14)	0.68037 (12)	0.0200 (3)
H3	0.3427	0.4095	0.7067	0.024*
C4	0.38279 (13)	0.31073 (14)	0.57999 (12)	0.0204 (4)
H4	0.3949	0.3817	0.5378	0.025*
C5	0.37916 (14)	0.09385 (15)	0.59905 (13)	0.0231 (4)
H5	0.3879	0.0132	0.5698	0.028*
C6	0.34992 (13)	0.10436 (15)	0.70058 (12)	0.0209 (3)
H6	0.3391	0.0317	0.7413	0.025*
O2	0.45237 (10)	0.44506 (10)	0.36499 (9)	0.0277 (3)
O3	0.45280 (10)	0.14311 (10)	0.36138 (9)	0.0281 (3)
C7	0.47821 (13)	0.36540 (14)	0.30229 (12)	0.0203 (3)
C8	0.47930 (13)	0.22876 (14)	0.30003 (12)	0.0199 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0358 (7)	0.0232 (6)	0.0229 (6)	−0.0057 (5)	0.0178 (5)	−0.0011 (4)
N1	0.0347 (8)	0.0223 (7)	0.0191 (7)	−0.0059 (6)	0.0158 (6)	−0.0027 (5)
N2	0.0204 (7)	0.0258 (7)	0.0153 (6)	−0.0003 (5)	0.0077 (5)	−0.0010 (5)
C1	0.0191 (8)	0.0226 (8)	0.0160 (7)	0.0010 (6)	0.0079 (6)	0.0016 (6)
C2	0.0160 (7)	0.0216 (8)	0.0151 (7)	−0.0004 (6)	0.0061 (6)	0.0006 (6)
C3	0.0255 (8)	0.0185 (7)	0.0179 (7)	−0.0018 (6)	0.0088 (6)	−0.0015 (6)
C4	0.0229 (8)	0.0223 (8)	0.0172 (7)	−0.0027 (6)	0.0070 (6)	0.0017 (6)
C5	0.0297 (9)	0.0206 (8)	0.0216 (8)	0.0026 (7)	0.0117 (7)	−0.0011 (6)
C6	0.0255 (8)	0.0201 (8)	0.0194 (7)	0.0003 (6)	0.0102 (6)	0.0031 (6)
O2	0.0445 (8)	0.0199 (6)	0.0233 (6)	0.0039 (5)	0.0170 (5)	−0.0024 (4)
O3	0.0474 (8)	0.0199 (6)	0.0250 (6)	−0.0009 (5)	0.0237 (6)	0.0010 (4)
C7	0.0249 (8)	0.0211 (8)	0.0162 (7)	−0.0004 (6)	0.0075 (6)	0.0008 (6)
C8	0.0237 (8)	0.0190 (7)	0.0186 (7)	0.0003 (6)	0.0086 (6)	−0.0007 (6)

Geometric parameters (Å, º)

O1—C1	1.2383 (18)	C3—C4	1.381 (2)
N1—H2N	0.88 (2)	C4—H4	0.950
N1—H1N	0.91 (2)	C5—H5	0.950
N1—C1	1.331 (2)	C5—C6	1.381 (2)
N2—H3N	1.15 (3)	C6—H6	0.950
N2—C4	1.3409 (19)	O2—C7	1.2384 (17)
N2—C5	1.3433 (19)	O3—H3N	1.39 (3)
C1—C2	1.518 (2)	O3—C8	1.2756 (18)
C2—C3	1.395 (2)	C7—C7^i	1.503 (3)
C2—C6	1.393 (2)	C7—C8	1.461 (2)
C3—H3	0.950	C8—C8^i	1.436 (3)
H2N—N1—H1N	120.3 (17)	N2—C4—H4	119.4
H2N—N1—C1	121.5 (12)	C3—C4—H4	119.4
H1N—N1—C1	117.9 (12)	N2—C5—H5	119.5
H3N—N2—C4	121.7 (12)	N2—C5—C6	121.08 (14)
H3N—N2—C5	117.6 (12)	H5—C5—C6	119.5
C4—N2—C5	120.63 (12)	C2—C6—C5	119.12 (14)
O1—C1—N1	123.88 (13)	C2—C6—H6	120.4
O1—C1—C2	119.14 (13)	C5—C6—H6	120.4
N1—C1—C2	116.98 (13)	H3N—O3—C8	117.1 (10)
C1—C2—C3	123.29 (13)	O2—C7—C7^i	136.55 (8)
C1—C2—C6	117.73 (13)	O2—C7—C8	134.76 (13)
C3—C2—C6	118.98 (13)	C7^i—C7—C8	88.69 (8)
C2—C3—H3	120.5	O3—C8—C7	134.56 (13)
C2—C3—C4	119.00 (14)	O3—C8—C8^i	134.12 (8)
H3—C3—C4	120.5	C7—C8—C8^i	91.31 (8)
N2—C4—C3	121.19 (13)
O1—C1—C2—C3	161.17 (14)	C4—N2—C5—C6	−0.5 (2)
O1—C1—C2—C6	−18.8 (2)	N2—C5—C6—C2	0.4 (2)
N1—C1—C2—C3	−18.6 (2)	C1—C2—C6—C5	−179.79 (14)
N1—C1—C2—C6	161.46 (14)	C3—C2—C6—C5	0.2 (2)
C1—C2—C3—C4	179.14 (14)	O2—C7—C8—O3	0.9 (3)
C6—C2—C3—C4	−0.9 (2)	O2—C7—C8—C8^i	−179.87 (19)
C5—N2—C4—C3	−0.2 (2)	C7^i—C7—C8—O3	−179.37 (18)
C2—C3—C4—N2	0.9 (2)	C7^i—C7—C8—C8^i	−0.11 (17)

Symmetry code: (i) −x+1, y, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H2N···O2^ii	0.88 (2)	2.03 (2)	2.8940 (19)	168.6 (17)
N1—H1N···O1^iii	0.91 (2)	2.01 (2)	2.9208 (18)	172.4 (17)
N2—H3N···O3	1.15 (3)	1.39 (3)	2.5322 (16)	171 (2)
C3—H3···O2^ii	0.95	2.57	3.3249 (19)	137
C4—H4···O2	0.95	2.48	3.2909 (19)	143
C5—H5···O3^iv	0.95	2.51	3.1921 (19)	129
C6—H6···O3^v	0.95	2.54	3.339 (2)	141

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