1H-Benzo[g]pteridine-2,4-dione

The structure of the title compound, C₁₀H₆N₄O₂, reported by Smalley et al. [(2021). Cryst. Growth Des. 22, 524–534] from powder diffraction data and ¹⁵N NMR spectroscopy, is confirmed using low-temperature data from a twinned crystal. The tautomer in the solid state is alloxazine (1H-benzo[g]pteridine-2,4-dione) rather than isoalloxazine (10H-benzo[g]pteridine-2,4-dione). In the extended structure, the mol­ecules form hydrogen-bonded chains propagating in the [01] direction through alternating centrosymmetric R²₂(8) rings with pairwise N—H...O inter­actions and centrosymmetric R²₂(8) rings with pairwise N—H...N inter­actions. The crystal chosen for data collection was found to be a non-merohedral twin (180° rotation about [001]) in a 0.446 (4):0.554 (6) domain ratio.

Key indicators

Structure: I

• Single-crystal X-ray study
• T = 90 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.048
• wR factor = 0.144
• Data-to-parameter ratio = 44.8

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT029_ALERT_3_C _diffrn_measured_fraction_theta_full value Low .      0.973 Why?
PLAT088_ALERT_3_C Poor Data / Parameter Ratio ....................       9.42 Note
PLAT340_ALERT_3_C Low Bond Precision on  C-C Bonds ...............    0.00413 Ang.
PLAT906_ALERT_3_C Large K Value in the Analysis of Variance ......      2.099 Check
PLAT911_ALERT_3_C Missing FCF Refl Between Thmin & STh/L=    0.600         84 Report

Alert level G
PLAT870_ALERT_4_G ALERTS Related to Twinning Effects Suppressed ..          ! Info
PLAT912_ALERT_4_G Missing # of FCF Reflections Above STh/L=  0.600         25 Note
PLAT931_ALERT_5_G CIFcalcFCF  Twin Law ( 0 0 1)         Est.d BASF       0.45 Check
PLAT931_ALERT_5_G CIFcalcFCF  Twin Law ( 1 2 1)         Est.d BASF       0.44 Check
PLAT933_ALERT_2_G Number of HKL-OMIT Records in Embedded .res File          7 Note
PLAT941_ALERT_3_G Average HKL Measurement Multiplicity ...........        4.8 Low

   0 ALERT level A = Most likely a serious problem - resolve or explain
   0 ALERT level B = A potentially serious problem, consider carefully
   5 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   6 ALERT level G = General information/check it is not something unexpected

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   6 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   2 ALERT type 5 Informative message, check

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Computing details

Data collection: APEX2 (Bruker, 2016); cell refinement: SAINT (Bruker, 2016); data reduction: SAINT (Bruker, 2016); program(s) used to solve structure: SHELXT2014/5 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2017/1 (Sheldrick, 2015b); molecular graphics: Mercury (Macrae et al., 2020); software used to prepare material for publication: publCIF (Westrip, 2010).

1H-Benzo[g]pteridine-2,4-dione

Crystal data

C10H6N4O2	Z = 2
Mr = 214.19	F(000) = 220
Triclinic, P1	Dx = 1.715 Mg m^−3
a = 5.8027 (2) Å	Cu Kα radiation, λ = 1.54184 Å
b = 7.5404 (3) Å	Cell parameters from 4433 reflections
c = 10.1345 (4) Å	θ = 4.6–69.1°
α = 70.483 (2)°	µ = 1.06 mm^−1
β = 84.150 (2)°	T = 90 K
γ = 84.208 (3)°	Plate, pale yellow
V = 414.72 (3) Å^3	0.11 × 0.06 × 0.02 mm

Data collection

Bruker Kappa APEXII DUO CCD diffractometer	6802 independent reflections
Radiation source: IµS microfocus	4832 reflections with I > 2σ(I)
QUAZAR multilayer optics monochromator	θmax = 69.4°, θmin = 4.6°
φ and ω scans	h = −7→7
Absorption correction: multi-scan (TWINABS; Bruker, 2001)	k = −9→9
Tmin = 0.774, Tmax = 0.979	l = −12→12
6802 measured reflections

Refinement

Refinement on F^2	Primary atom site location: dual
Least-squares matrix: full	Hydrogen site location: mixed
R[F^2 > 2σ(F^2)] = 0.048	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.144	w = 1/[σ^2(Fo^2) + (0.0713P)^2 + 0.0047P] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max < 0.001
6802 reflections	Δρmax = 0.26 e Å^−3
152 parameters	Δρmin = −0.28 e Å^−3
0 restraints

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. Refined as a 2-component twin, by 180 deg. rotation about reciprocal 0 0 1. Refinement was vs. an HKLF 5 file prepared using TWINABS. The refined BASF parameter is 0.446 (4). Seven outlier reflections were omitted from the refinement.

All H atoms were located in difference maps and those on C were thereafter treated as riding in geometrically idealized positions with C—H distances 0.95 Å. Coordinates of the N—H hydrogen atom were refined. U_iso(H) values were assigned as 1.2U_eq of the attached atom.

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

	x	y	z	Uiso*/Ueq
O1	0.6141 (4)	0.4107 (3)	0.8404 (2)	0.0215 (6)
O2	−0.0946 (3)	0.7091 (3)	0.8834 (2)	0.0213 (6)
N1	0.2942 (4)	0.8937 (4)	0.4485 (2)	0.0150 (6)
N2	0.6687 (4)	0.6283 (4)	0.5564 (2)	0.0160 (6)
N3	0.2614 (4)	0.5646 (4)	0.8587 (3)	0.0166 (6)
H3N	0.231 (5)	0.487 (5)	0.949 (4)	0.020*
N4	0.1014 (4)	0.7992 (4)	0.6692 (2)	0.0160 (6)
H4N	−0.018 (6)	0.884 (5)	0.638 (3)	0.019*
C1	0.4878 (5)	0.8700 (4)	0.3647 (3)	0.0154 (7)
C2	0.6759 (5)	0.7382 (4)	0.4193 (3)	0.0154 (7)
C3	0.8747 (5)	0.7183 (4)	0.3300 (3)	0.0165 (7)
H3	1.001181	0.631113	0.366387	0.020*
C4	0.8827 (5)	0.8255 (5)	0.1911 (3)	0.0181 (7)
H4	1.014200	0.811737	0.130392	0.022*
C5	0.6963 (5)	0.9562 (5)	0.1379 (3)	0.0179 (7)
H5	0.704994	1.030108	0.041346	0.022*
C6	0.5034 (5)	0.9801 (5)	0.2209 (3)	0.0171 (7)
H6	0.380553	1.069981	0.182484	0.020*
C7	0.2926 (5)	0.7827 (4)	0.5806 (3)	0.0135 (6)
C8	0.4803 (5)	0.6503 (4)	0.6354 (3)	0.0147 (7)
C9	0.4648 (5)	0.5301 (5)	0.7850 (3)	0.0163 (7)
C10	0.0784 (5)	0.6913 (5)	0.8079 (3)	0.0164 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0173 (11)	0.0228 (13)	0.0192 (11)	0.0062 (9)	−0.0022 (9)	−0.0018 (9)
O2	0.0187 (11)	0.0237 (13)	0.0164 (10)	0.0027 (9)	0.0043 (9)	−0.0024 (9)
N1	0.0137 (12)	0.0175 (15)	0.0133 (13)	−0.0003 (10)	−0.0001 (10)	−0.0047 (11)
N2	0.0168 (12)	0.0151 (14)	0.0160 (13)	−0.0017 (10)	0.0009 (10)	−0.0055 (11)
N3	0.0150 (13)	0.0179 (14)	0.0124 (12)	0.0033 (10)	0.0007 (10)	−0.0008 (10)
N4	0.0141 (13)	0.0180 (14)	0.0125 (12)	0.0046 (11)	−0.0020 (10)	−0.0016 (10)
C1	0.0145 (14)	0.0168 (16)	0.0163 (16)	−0.0015 (12)	−0.0001 (12)	−0.0074 (13)
C2	0.0159 (14)	0.0156 (16)	0.0143 (15)	−0.0015 (12)	−0.0017 (12)	−0.0040 (13)
C3	0.0139 (14)	0.0174 (17)	0.0199 (15)	−0.0003 (12)	−0.0012 (12)	−0.0085 (13)
C4	0.0164 (15)	0.0220 (17)	0.0167 (15)	−0.0043 (12)	0.0015 (12)	−0.0071 (12)
C5	0.0197 (15)	0.0195 (17)	0.0140 (15)	−0.0025 (12)	−0.0010 (12)	−0.0044 (12)
C6	0.0151 (14)	0.0195 (17)	0.0170 (15)	0.0018 (12)	−0.0030 (12)	−0.0068 (13)
C7	0.0140 (14)	0.0127 (16)	0.0139 (14)	−0.0014 (11)	0.0000 (12)	−0.0048 (12)
C8	0.0159 (15)	0.0149 (16)	0.0133 (16)	0.0006 (12)	−0.0048 (12)	−0.0039 (13)
C9	0.0162 (15)	0.0176 (17)	0.0152 (16)	−0.0007 (12)	−0.0014 (12)	−0.0056 (13)
C10	0.0155 (15)	0.0176 (17)	0.0158 (15)	0.0010 (12)	−0.0013 (12)	−0.0056 (12)

Geometric parameters (Å, º)

O1—C9	1.217 (3)	C1—C6	1.414 (4)
O2—C10	1.224 (4)	C1—C2	1.422 (4)
N1—C7	1.321 (4)	C2—C3	1.420 (4)
N1—C1	1.372 (4)	C3—C4	1.368 (4)
N2—C8	1.318 (4)	C3—H3	0.9500
N2—C2	1.358 (4)	C4—C5	1.407 (4)
N3—C10	1.372 (4)	C4—H4	0.9500
N3—C9	1.381 (4)	C5—C6	1.364 (4)
N3—H3N	0.92 (3)	C5—H5	0.9500
N4—C10	1.369 (4)	C6—H6	0.9500
N4—C7	1.377 (4)	C7—C8	1.423 (4)
N4—H4N	0.90 (3)	C8—C9	1.483 (4)
C7—N1—C1	115.5 (3)	C5—C4—H4	120.0
C8—N2—C2	116.9 (3)	C6—C5—C4	122.0 (3)
C10—N3—C9	127.3 (3)	C6—C5—H5	119.0
C10—N3—H3N	113 (2)	C4—C5—H5	119.0
C9—N3—H3N	119 (2)	C5—C6—C1	119.5 (3)
C10—N4—C7	123.5 (3)	C5—C6—H6	120.2
C10—N4—H4N	116 (2)	C1—C6—H6	120.2
C7—N4—H4N	121 (2)	N1—C7—N4	118.0 (3)
N1—C1—C6	119.7 (3)	N1—C7—C8	123.0 (3)
N1—C1—C2	121.5 (3)	N4—C7—C8	119.0 (3)
C6—C1—C2	118.8 (3)	N2—C8—C7	122.0 (3)
N2—C2—C3	118.8 (3)	N2—C8—C9	118.3 (3)
N2—C2—C1	121.1 (3)	C7—C8—C9	119.8 (3)
C3—C2—C1	120.1 (3)	O1—C9—N3	121.7 (3)
C4—C3—C2	119.5 (3)	O1—C9—C8	124.5 (3)
C4—C3—H3	120.3	N3—C9—C8	113.8 (3)
C2—C3—H3	120.3	O2—C10—N4	121.8 (3)
C3—C4—C5	120.1 (3)	O2—C10—N3	121.6 (3)
C3—C4—H4	120.0	N4—C10—N3	116.6 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N3—H3N···O2^i	0.92 (3)	2.00 (4)	2.883 (3)	162 (3)
N4—H4N···N1^ii	0.90 (3)	2.22 (3)	3.114 (3)	176 (3)
C3—H3···N2^iii	0.95	2.58	3.520 (4)	173
C6—H6···O2^ii	0.95	2.21	3.158 (4)	173

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