7-Meth­oxy-2,3-dioxo-1,4-dihydro­quinoxalin-6-aminium chloride monohydrate

Single crystals of the title compound, C₉H₁₀N₃O₃⁺·Cl^-·H₂O, were obtained by recrystallization from hydro­chloric acid. The cations stack along the crystallographic a direction. The 2,3-dioxo-1,4-dihydro­quinoxaline group shows a significant deviation from planarity [r.m.s. deviation from the best plane = 0.063 (2) Å]. Hydrogen bonding links the cations, chloride anions and water molecules to form an extended three-dimensional architecture.

S1. Comment

The compound 6-amino-7-methoxy-1,4-dihydroquinoxaline-2,3-dione, (I) (see scheme), is an intermediate in the synthesis of quinoxaline-based azo pigments (Herbst & Hunger, 1995; Alfter et al., 1996; Dietz et al., 2001; Schupp et al., 2002; Blum et al., 2004; Schweikart et al., 2007). Compound (I) is synthesized from 2,4,5-triamino-1-methoxybenzene and oxalylchloride. Research on quinoxaline pigments led to Pigment Yellow 213 (Metz & Weber, 1998; Stengel-Rutkowski & Metz, 2000; Metz & Morgenroth, 2009; Schmidt et al., 2009) which is used in water-based automotive coatings. Compound (I) is a dull yellow powder which is poorly soluble; hence, no single crystals have, to date, been grown.

In order to grow crystals of (I) and determine its crystal structure as well as to search for different crystallographic phases, hydrates or solvates, a polymorph screening was performed. Therefore, different crystallization methods were used including (i) recrystallization from various solvents and solvent mixtures by heating and subsequent slow cooling, (ii) overlaying a solution of the compound by an anti-solvent, (iii) diffusion of an anti-solvent into a solution of the compound via the gas phase. The solvents included the most common organic solvents, e.g. dimethylsulfoxide, N-methylpyrrolidone, ethers, esters, alcohols, acids and water. According to X-ray powder diffraction, only two phases, the technical phase and the hydrochloride monohydrate phase, have been found.

Single crystals of the title compound, (II), could be obtained by recrystallizing compound (I) in half-concentrated hydrochloric acid. The molecular structure is shown in Fig. 1. The 2,3-dioxo-1,4-dihydroquinoxaline group shows a significant distortion from planarity. The root-mean- square deviation from the best plane, excluding the H atoms, is 0.063 (2) Å. The largest deviation from the best plane is found for atoms O1, C2 and C8 [0.126 (2), 0.088 (2) and 0.089 (2) Å, respectively]. The benzene ring is less distorted [mean deviation from the plane: 0.015 (2) Å] than the pyrazine ring [mean deviation from the plane: 0.022 (2) Å]. The angle between the planes of the two six-membered rings is 4.0 (1)°. To check whether this distortion from planarity is common for this group or if it may result from crystal-packing forces, the planarity of all 28 entries in the Cambridge Structural Database (CSD; Allen, 2002) containing the 2,3-dioxo-1,4-dihydroquinoxaline group was calculated. The results are listed in Table 1. In those cases where a crystal structure has been determined more than once, very similar values are obtained, showing that the values reported in Table 1 may be very reliable. The mean-square displacement ranges from 0.005 to 0.071 Å. The non-planarity of the title compound is in the upper range of Table 1. Only one compound shows a larger distortion. The large variation among the compounds suggests that the deviation from planarity is considerably affected by crystal-packing forces. This observation is further supported by the fact that rather different deviations from planarity are observed in crystal structures that contain independent molecules (refcodes CNIXQX, RAVFUQ and RAVGAX) or in different hydrates of the same compound (refcodes SUHHEI, RAVFOK and RAVFUQ). In most structures the 2,3-dioxo-1,4-dihydroquinoxaline groups form stacks. In some structures the 2,3-dioxo-1,4-dihydroquinoxaline groups lie in pairs with their molecular planes aligned. Only a few structures do not show a parallel arrangement of the molecular planes. The non-planarity of the 2,3-dioxo-1,4-dihydroquinoxaline group, however, does not depend on whether the molecules align in stacks or not.

The crystal structure of the title compound is shown in Fig. 2. The molecules stack along the crystallographic a direction. Adjacent molecules in the stack are related by a glide planes. The angle between the neighbouring 2,3-dioxo-1,4-dihydroquinoxaline planes in the stack is 3.0 (1)°. The smallest interplanar C···C distance in the stack is 3.247 (4) Å between C5 and C6 (at x - 1/2, y, -z + 1/2). There also is a short intermolecular contact distance of 3.188 (4) Å betweeen O1 and C8 (at x - 1/2, y, -z + 1/2). The methoxy group of (II) is almost coplanar with the bicyclic moiety – the torsion angle C7—C8—O3—C9 is -9.5 (4)°.

The cations, chloride anions and water molecules are connected by a three-dimensional framework of hydrogen bonds involving O—H···Cl^-, N—H···Cl^-, O—H···O and N—H···O interactions (Table 2). The N3—H3B bond is a donor of a bifurcated hydrogen bond: an intermolecular hydrogen bond to a water molecule and an intramolecular hydrogen bond to the methoxy O atom. The water molecule is a donor of two hydrogen bonds and an acceptor of one hydrogen bond. The Cl^- anion accepts hydrogen bonds from three different cations and from a water molecule.

The most prominent features of the hydrogen-bond network are two 12-membered rings. The first one is built from two molecules and one chloride anion (Fig. 3a). According to graph set notation (Etter, 1990; Bernstein et al., 1995) this ring, containing two acceptors and three donors, is denoted as R²₃ (12). The second ring is a R⁴₆ (12) built from two molecules of (I), two chloride anions and two water molecules (Fig. 3b). A full graph set analysis revealed 56 graph sets for first-, second- and third-order level. Selected graph sets for chain and ring sets are shown in Table 3. C—H···O interactions were not included in this analysis as they are much weaker than interactions of NH and OH groups. For other quinoxalinedione derivatives, extensive graph set analyses are reported in an earlier work (Kubicki et al., 1996). These graph sets are considerably different for [to?] those found for compound (II).

The title compound contains two amide (CONH) groups in cis conformation. Generally, cis-amide groups form eight-membered rings R²₂(8) or C²₂(8) chains, as observed e.g. in many benzimidazolone derivatives (Van de Streek et al., 2009). In contrast, the cis-amide groups of compound (II) show neither a ring, nor a chain motif with another amide group, but both NH groups form hydrogen bonds with the chloride anion. This can be explained by the negative charge of the chloride anion which makes the chloride anion a much better hydrogen-bond acceptor than a carbonyl group of an amide fragment.

Related literature

For related literature, see: Alfter et al. (1996); Allen (2002); Bernstein et al. (1995); Blum et al. (2004); Dietz et al. (2001); Etter (1990); Herbst & Hunger (1995); Kubicki et al. (1996); Metz & Morgenroth (2009); Metz & Weber (1998); Schmidt et al. (2009); Schupp et al. (2002); Schweikart et al. (2007); Stengel-Rutkowski & Metz (2000).

S2. Experimental

The raw material of compound (II) was industrially produced, and obtained from Clariant GmbH, Germany. Single crystals of compound (II) could be grown from hydrochloric acid: in a flask 30 mg of (I) were dissolved in a mixture of 2 ml of concentrated hydrochloric acid and 2 ml of water. Subsequently, the mixture was placed in an oven at 343 K to slowly concentrate the solution. After 48 h yellow–brown rod-shaped crystals of compound (II), with sizes of about 0.6 x 0.06 x 0.05 mm, were obtained.

S3. Refinement

The H atoms of the water molecule were taken from a difference synthesis and refined. The H atoms at C and N atoms were also taken from a difference synthesis but were constrained using: C_planar—H = 0.95 Å, C_methyl—H = 0.98 Å, N_planar—H = 0.88 Å, N_tetrahedral—H = 0.91 Å, H_iso(H) = 1.2U_eq(C_planar), U_iso(H) = 1.5U_eq(C_methyl) and U_iso(H) = 1.5U_eq(N). The torsion angles about the C1—N3 and O3—C9 bonds were refined.

Computing details

Data collection: SMART (Siemens, 1995); cell refinement: SMART (Siemens, 1995); data reduction: SAINT (Siemens, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: publCIF (Westrip, 2009).

Figures

Fig. 1. Molecular structure of compound (II), with atom labels and anisotropic displacement ellipsoids (drawn at 50% probability level) for non-H atoms. Fig. 2. Section of molecular packing of compound (II) showing the hydrogen-bond architecture; view direction [100]. Only the upper layer of molecules is shown. The hydrogen bonds are drawn as dashed lines. Fig. 3. Third-order graph sets R^23 (12) (a) and R^46 (12) (b) of compound (I). The atoms involved are highlighted and appendant hydrogen bonds are drawn as dashed lines. Fig. 4: Third order graph sets R^23 (12) (a) and R^46 (12) (b) of compound I. The involved atoms are highlighted and appendant hydrogen bonds are drawn as dashed lines.

7-Methoxy-2,3-dioxo-1,4-dihydroquinoxalin-6-aminium chloride monohydrate

Crystal data

C9H10N3O3^+·Cl^−·H2O	F(000) = 1088
Mr = 261.67	Dx = 1.565 Mg m^−3
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 81 reflections
a = 6.7339 (11) Å	θ = 3–23°
b = 15.469 (4) Å	µ = 0.35 mm^−1
c = 21.327 (4) Å	T = 168 K
V = 2221.5 (8) Å^3	Rod, yellow brown
Z = 8	0.60 × 0.06 × 0.05 mm

Data collection

Siemens SMART 1K CCD diffractometer	2609 independent reflections
Radiation source: normal-focus sealed tube	1375 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.153
ω scans	θmax = 28.0°, θmin = 1.9°
Absorption correction: multi-scan (SADABS; Bruker, 2000)	h = −8→8
Tmin = 0.890, Tmax = 0.983	k = −20→20
30122 measured reflections	l = −27→27

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)] = 0.054	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.117	H atoms treated by a mixture of independent and constrained refinement
S = 0.99	w = 1/[σ^2(Fo^2) + (0.05P)^2 + 0.4P] where P = (Fo^2 + 2Fc^2)/3
2609 reflections	(Δ/σ)max = 0.002
164 parameters	Δρmax = 0.30 e Å^−3
0 restraints	Δρmin = −0.29 e Å^−3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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
Cl1	0.09665 (11)	0.54666 (5)	0.13838 (3)	0.0278 (2)
O1	0.1500 (4)	0.93846 (17)	0.03799 (11)	0.0412 (7)
O2	−0.0706 (3)	0.95135 (13)	0.17874 (9)	0.0278 (5)
O3	0.0349 (3)	0.80258 (13)	0.11462 (9)	0.0278 (5)
O7	0.1180 (3)	0.73505 (12)	0.46662 (8)	0.0262 (5)
N1	−0.0180 (3)	0.88225 (14)	0.27058 (10)	0.0203 (6)
H1A	−0.0444	0.9299	0.2915	0.030*
N4	0.0579 (3)	0.73227 (15)	0.20767 (10)	0.0199 (6)
H4A	0.0787	0.6831	0.1880	0.030*
N6	0.1604 (4)	0.58159 (14)	0.40701 (10)	0.0253 (6)
H6A	0.0810	0.5374	0.3942	0.038*
H6B	0.1407	0.5915	0.4486	0.038*
H6C	0.2898	0.5673	0.4003	0.038*
C2	−0.0254 (4)	0.88588 (18)	0.20734 (13)	0.0202 (7)
C3	0.0256 (4)	0.80313 (19)	0.17224 (13)	0.0195 (7)
C4A	0.0607 (4)	0.73109 (18)	0.27306 (12)	0.0189 (7)
C5	0.0981 (4)	0.65599 (17)	0.30703 (13)	0.0200 (6)
H5A	0.1143	0.6023	0.2860	0.024*
C6	0.1114 (4)	0.66020 (18)	0.37120 (13)	0.0212 (7)
C7	0.0891 (4)	0.73797 (18)	0.40358 (12)	0.0205 (7)
C8	0.0428 (4)	0.81223 (18)	0.37036 (13)	0.0200 (7)
H8A	0.0213	0.8653	0.3917	0.024*
C8A	0.0282 (4)	0.80835 (17)	0.30518 (13)	0.0175 (7)
C9	0.1298 (5)	0.81634 (18)	0.49890 (13)	0.0296 (8)
H9A	0.2330	0.8522	0.4796	0.044*
H9B	0.1629	0.8062	0.5430	0.044*
H9C	0.0016	0.8461	0.4961	0.044*
H1B	0.120 (6)	0.894 (3)	0.0609 (17)	0.065 (14)*
H1C	0.237 (6)	0.970 (3)	0.0626 (18)	0.075 (15)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.0375 (4)	0.0185 (4)	0.0273 (4)	0.0023 (4)	0.0008 (4)	0.0001 (3)
O1	0.0607 (18)	0.0351 (16)	0.0279 (14)	−0.0143 (13)	−0.0060 (13)	0.0022 (12)
O2	0.0389 (14)	0.0181 (11)	0.0264 (11)	0.0034 (11)	−0.0049 (10)	0.0026 (10)
O3	0.0361 (14)	0.0287 (13)	0.0185 (11)	0.0014 (10)	−0.0011 (10)	−0.0014 (9)
O7	0.0425 (14)	0.0189 (11)	0.0172 (11)	−0.0002 (10)	−0.0008 (10)	−0.0013 (9)
N1	0.0261 (14)	0.0148 (13)	0.0199 (14)	0.0035 (11)	−0.0001 (11)	−0.0022 (10)
N4	0.0231 (15)	0.0171 (13)	0.0195 (13)	0.0015 (11)	0.0004 (11)	−0.0033 (11)
N6	0.0363 (16)	0.0199 (14)	0.0197 (13)	−0.0012 (12)	0.0007 (11)	−0.0035 (11)
C2	0.0184 (16)	0.0183 (16)	0.0240 (17)	−0.0008 (13)	−0.0042 (13)	−0.0009 (14)
C3	0.0142 (16)	0.0200 (17)	0.0243 (18)	−0.0028 (13)	−0.0022 (13)	0.0007 (14)
C4A	0.0167 (16)	0.0180 (16)	0.0219 (17)	−0.0026 (13)	−0.0006 (13)	−0.0007 (13)
C5	0.0215 (16)	0.0168 (16)	0.0217 (16)	−0.0002 (14)	0.0025 (13)	−0.0058 (12)
C6	0.0212 (16)	0.0149 (15)	0.0275 (18)	−0.0018 (14)	0.0001 (14)	0.0023 (13)
C7	0.0214 (16)	0.0215 (17)	0.0188 (16)	−0.0031 (14)	0.0019 (13)	−0.0014 (13)
C8	0.0226 (17)	0.0151 (16)	0.0223 (17)	−0.0008 (13)	0.0005 (13)	−0.0038 (13)
C8A	0.0161 (16)	0.0145 (16)	0.0219 (16)	0.0002 (12)	−0.0017 (12)	0.0010 (13)
C9	0.047 (2)	0.0248 (18)	0.0171 (16)	−0.0010 (16)	−0.0002 (15)	−0.0047 (13)

Geometric parameters (Å, º)

O1—H1B	0.87 (4)	N6—H6B	0.9100
O1—H1C	0.93 (4)	N6—H6C	0.9100
O2—C2	1.221 (3)	C2—C3	1.522 (4)
O3—C3	1.230 (3)	C4A—C5	1.392 (4)
O7—C7	1.359 (3)	C4A—C8A	1.395 (4)
O7—C9	1.436 (3)	C5—C6	1.373 (4)
N1—C2	1.351 (3)	C5—H5A	0.9500
N1—C8A	1.396 (3)	C6—C7	1.395 (4)
N1—H1A	0.8800	C7—C8	1.385 (4)
N4—C3	1.349 (3)	C8—C8A	1.395 (4)
N4—C4A	1.395 (3)	C8—H8A	0.9500
N4—H4A	0.8800	C9—H9A	0.9800
N6—C6	1.474 (3)	C9—H9B	0.9800
N6—H6A	0.9100	C9—H9C	0.9800
H1B—O1—H1C	105 (3)	C8A—C4A—N4	118.5 (3)
C7—O7—C9	116.9 (2)	C6—C5—C4A	119.4 (2)
C2—N1—C8A	124.7 (2)	C6—C5—H5A	120.3
C2—N1—H1A	117.6	C4A—C5—H5A	120.3
C8A—N1—H1A	117.6	C5—C6—C7	121.8 (3)
C3—N4—C4A	124.9 (2)	C5—C6—N6	119.5 (2)
C3—N4—H4A	117.5	C7—C6—N6	118.6 (2)
C4A—N4—H4A	117.5	O7—C7—C8	124.4 (2)
C6—N6—H6A	109.5	O7—C7—C6	116.5 (2)
C6—N6—H6B	109.5	C8—C7—C6	119.1 (3)
H6A—N6—H6B	109.5	C7—C8—C8A	119.3 (3)
C6—N6—H6C	109.5	C7—C8—H8A	120.3
H6A—N6—H6C	109.5	C8A—C8—H8A	120.3
H6B—N6—H6C	109.5	C4A—C8A—C8	121.0 (3)
O2—C2—N1	122.8 (3)	C4A—C8A—N1	118.5 (2)
O2—C2—C3	120.5 (3)	C8—C8A—N1	120.5 (2)
N1—C2—C3	116.6 (3)	O7—C9—H9A	109.5
O3—C3—N4	123.1 (3)	O7—C9—H9B	109.5
O3—C3—C2	120.6 (3)	H9A—C9—H9B	109.5
N4—C3—C2	116.4 (2)	O7—C9—H9C	109.5
C5—C4A—C8A	119.2 (3)	H9A—C9—H9C	109.5
C5—C4A—N4	122.3 (3)	H9B—C9—H9C	109.5
C8A—N1—C2—O2	178.4 (3)	C9—O7—C7—C6	169.4 (3)
C8A—N1—C2—C3	−1.4 (4)	C5—C6—C7—O7	−175.9 (3)
C4A—N4—C3—O3	175.9 (3)	N6—C6—C7—O7	1.0 (4)
C4A—N4—C3—C2	−4.4 (4)	C5—C6—C7—C8	3.2 (4)
O2—C2—C3—O3	4.9 (4)	N6—C6—C7—C8	−180.0 (3)
N1—C2—C3—O3	−175.3 (3)	O7—C7—C8—C8A	176.2 (3)
O2—C2—C3—N4	−174.8 (3)	C6—C7—C8—C8A	−2.8 (4)
N1—C2—C3—N4	5.1 (4)	C5—C4A—C8A—C8	3.3 (4)
C3—N4—C4A—C5	−178.9 (3)	N4—C4A—C8A—C8	−175.6 (3)
C3—N4—C4A—C8A	−0.1 (4)	C5—C4A—C8A—N1	−177.1 (3)
C8A—C4A—C5—C6	−3.0 (4)	N4—C4A—C8A—N1	4.0 (4)
N4—C4A—C5—C6	175.9 (3)	C7—C8—C8A—C4A	−0.4 (4)
C4A—C5—C6—C7	−0.2 (5)	C7—C8—C8A—N1	−180.0 (3)
C4A—C5—C6—N6	−177.1 (2)	C2—N1—C8A—C4A	−3.1 (4)
C9—O7—C7—C8	−9.5 (4)	C2—N1—C8A—C8	176.4 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N4—H4A···Cl1	0.88	2.36	3.240 (3)	173
N1—H1A···Cl1^i	0.88	2.37	3.243 (2)	171
N6—H6A···O2^ii	0.91	2.05	2.787 (3)	137
N6—H6B···O7	0.91	2.26	2.708 (3)	110
N6—H6B···O1^iii	0.91	1.96	2.811 (3)	154
N6—H6C···Cl1^iv	0.91	2.25	3.140 (3)	166
O1—H1B···O3	0.87 (4)	1.91 (4)	2.773 (3)	175 (4)
O1—H1C···Cl1^v	0.93 (4)	2.30 (4)	3.209 (3)	169 (3)
C5—H5A···O2^ii	0.95	2.47	3.185 (3)	132
C9—H9B···O3^iii	0.98	2.43	3.144 (4)	129

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