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A second C2/c polymorph of butobarbitone (5-butyl-5-ethyl­barbituric acid), C10H16N2O3, and a third polymorph overall, has been obtained after prolonged standing of an aqueous solution from which the first polymorph had been crystallized. It has the same space group as the first polymorph at room temperature, but very different cell parameters from both its room-temperature and low-temperature forms (the second polymorph), which are related by a displacive phase transition [Nichol & Clegg (2005). Acta Cryst. C61, o297–o299] with the low-temperature form having space group P21/n. The new polymorph shows no phase transition over the temperature range 150–270 K and has a higher density than the first and second polymorphs. N—H...O hydrogen bonds link the mol­ecules into tapes, which inter­weave in the crystal structure.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807045448/fl2163sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536807045448/fl2163Isup2.hkl
Contains datablock I

CCDC reference: 663826

Key indicators

  • Single-crystal X-ray study
  • T = 150 K
  • Mean [sigma](C-C) = 0.002 Å
  • R factor = 0.039
  • wR factor = 0.108
  • Data-to-parameter ratio = 17.7

checkCIF/PLATON results

No syntax errors found



Alert level C PLAT220_ALERT_2_C Large Non-Solvent C Ueq(max)/Ueq(min) ... 2.52 Ratio
0 ALERT level A = In general: serious problem 0 ALERT level B = Potentially serious problem 1 ALERT level C = Check and explain 0 ALERT level G = General alerts; check 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 0 ALERT type 3 Indicator that the structure quality may be low 0 ALERT type 4 Improvement, methodology, query or suggestion 0 ALERT type 5 Informative message, check

Comment top

We have previously reported a temperature-induced phase transition in butobarbitone, (I), with the room-temperature structure determined in space group C2/c (polymorph 1, originally reported by Bideau, 1971), while at 120 K the space group is P21/n (polymorph 2, Nichol & Clegg, 2005). We report here a third polymorph of (I). The space group of this third polymorph is C2/c with Z' = 1 but the unit-cell parameters are quite different from those of the previous structures.

The unit cell volume in this new polymorph is 2265.5 (8) Å3 and this is lower than the P21/n polymorph at low temperature [which is 2356.2 (4) Å3]. A unit cell determination at 270 K on the same crystal showed only the small expected expansion in the cell parameters and so this third polymorph does not appear to undergo a phase transition within the temperature range from 150 to 270 K.

The molecular structure of (I) is shown in Fig. 1. In common with both reported polymorphs, R22(6) N–H···O hydrogen bonding interactions link the butobarbitone molecules into an infinite hydrogen-bonded tape. Differences are found in the crystal packing. As shown in Fig. 2 the hydrogen-bonded tapes interweave, while in the previously-reported polymorphs the ribbons form roughly parallel stacks.

The higher density of this new polymorph, and the fact that it was formed slowly from a solution from which the first polymorph had already been obtained more quickly, suggest that this is the thermodynamically more stable form.

Related literature top

See Bideau (1971) for the original room-temperature determination of polymorph 1, and Nichol & Clegg (2005) for details of the temperature-induced phase transition to polymorph 2.

Experimental top

Equimolar amounts of butobarbitone and ammonium carbonate were dissolved in distilled water and heated until boiling. Small colourless crystals of polymorph 1 grew over a period of two days on standing at room temperature in a sealed sample vial. Large colourless crystals of this new polymorph 3 (I) were observed after the sample vial had stood undisturbed for 17 months. Some of the smaller crystals were also still present in the vial.

Refinement top

All H atoms were located in a difference map. CH2 H atoms were then idealized (C—H = 0.99 Å) and refined as riding with Uiso(H) = 1.2Ueq(C). The methyl H atoms were geometrically positioned (C—H = 0.98 Å) and refined as riding with Uiso(H) = 1.5Ueq(C) and free rotation about the C—C bond. Nitrogen-bound H atoms were freely refined, giving N—H distances of 0.882 (19) and 0.883 (16) Å.

Structure description top

We have previously reported a temperature-induced phase transition in butobarbitone, (I), with the room-temperature structure determined in space group C2/c (polymorph 1, originally reported by Bideau, 1971), while at 120 K the space group is P21/n (polymorph 2, Nichol & Clegg, 2005). We report here a third polymorph of (I). The space group of this third polymorph is C2/c with Z' = 1 but the unit-cell parameters are quite different from those of the previous structures.

The unit cell volume in this new polymorph is 2265.5 (8) Å3 and this is lower than the P21/n polymorph at low temperature [which is 2356.2 (4) Å3]. A unit cell determination at 270 K on the same crystal showed only the small expected expansion in the cell parameters and so this third polymorph does not appear to undergo a phase transition within the temperature range from 150 to 270 K.

The molecular structure of (I) is shown in Fig. 1. In common with both reported polymorphs, R22(6) N–H···O hydrogen bonding interactions link the butobarbitone molecules into an infinite hydrogen-bonded tape. Differences are found in the crystal packing. As shown in Fig. 2 the hydrogen-bonded tapes interweave, while in the previously-reported polymorphs the ribbons form roughly parallel stacks.

The higher density of this new polymorph, and the fact that it was formed slowly from a solution from which the first polymorph had already been obtained more quickly, suggest that this is the thermodynamically more stable form.

See Bideau (1971) for the original room-temperature determination of polymorph 1, and Nichol & Clegg (2005) for details of the temperature-induced phase transition to polymorph 2.

Computing details top

Data collection: COLLECT (Nonius, 1998); cell refinement: EVALCCD (Duisenberg et al., 2003); data reduction: EVALCCD (Duisenberg et al., 2003); program(s) used to solve structure: SHELXTL (Sheldrick, 2001); program(s) used to refine structure: SHELXTL (Sheldrick, 2001); molecular graphics: DIAMOND (Brandenburg & Putz, 2004) and Mercury (Bruno et al., 2002); software used to prepare material for publication: SHELXTL (Sheldrick, 2001) and local programs.

Figures top
[Figure 1] Fig. 1. The molecular structure of (I) with displacement ellipsoids at the 50% probability level and hydrogen atoms as small spheres.
[Figure 2] Fig. 2. The interweaving hydrogen-bonded tapes found in (I).
5-butyl-5-ethylbarbituric acid top
Crystal data top
C10H16N2O3F(000) = 912
Mr = 212.25Dx = 1.245 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2ycCell parameters from 6280 reflections
a = 19.519 (4) Åθ = 2.5–27.5°
b = 7.6868 (15) ŵ = 0.09 mm1
c = 15.117 (3) ÅT = 150 K
β = 92.77 (3)°Block, colourless
V = 2265.5 (8) Å30.37 × 0.35 × 0.13 mm
Z = 8
Data collection top
Nonius KappaCCD
diffractometer
2585 independent reflections
Radiation source: sealed tube1958 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.034
φ and ω scansθmax = 27.5°, θmin = 4.8°
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
h = 2525
Tmin = 0.917, Tmax = 0.988k = 99
12332 measured reflectionsl = 1819
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.039Hydrogen site location: difference Fourier map
wR(F2) = 0.108H atoms treated by a mixture of independent and constrained refinement
S = 1.08 w = 1/[σ2(Fo2) + (0.0526P)2 + 1.0348P]
where P = (Fo2 + 2Fc2)/3
2585 reflections(Δ/σ)max < 0.001
146 parametersΔρmax = 0.28 e Å3
0 restraintsΔρmin = 0.20 e Å3
Crystal data top
C10H16N2O3V = 2265.5 (8) Å3
Mr = 212.25Z = 8
Monoclinic, C2/cMo Kα radiation
a = 19.519 (4) ŵ = 0.09 mm1
b = 7.6868 (15) ÅT = 150 K
c = 15.117 (3) Å0.37 × 0.35 × 0.13 mm
β = 92.77 (3)°
Data collection top
Nonius KappaCCD
diffractometer
2585 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
1958 reflections with I > 2σ(I)
Tmin = 0.917, Tmax = 0.988Rint = 0.034
12332 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0390 restraints
wR(F2) = 0.108H atoms treated by a mixture of independent and constrained refinement
S = 1.08Δρmax = 0.28 e Å3
2585 reflectionsΔρmin = 0.20 e Å3
146 parameters
Special details top

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 (Å2) top
xyzUiso*/Ueq
O10.47791 (4)0.62343 (12)0.40519 (6)0.0242 (2)
O20.33382 (5)0.26565 (12)0.54285 (6)0.0262 (2)
O30.24583 (5)0.55071 (13)0.30083 (6)0.0296 (3)
N10.40634 (5)0.43550 (14)0.46817 (7)0.0191 (2)
H1N0.4389 (9)0.411 (2)0.5089 (11)0.035 (4)*
N20.29072 (6)0.40867 (15)0.42063 (7)0.0218 (3)
H2N0.2499 (8)0.364 (2)0.4287 (10)0.028 (4)*
C10.42106 (6)0.55569 (16)0.40434 (8)0.0176 (3)
C20.34256 (6)0.36347 (16)0.48085 (8)0.0188 (3)
C30.29594 (6)0.51903 (16)0.34869 (8)0.0199 (3)
C40.36613 (6)0.59673 (16)0.33256 (8)0.0191 (3)
C50.35829 (7)0.79708 (18)0.32390 (10)0.0275 (3)
H5A0.40400.84820.31480.033*
H5B0.32870.82300.27050.033*
C60.32798 (10)0.8851 (2)0.40337 (12)0.0442 (4)
H6A0.28260.83620.41280.066*
H6B0.32381.01040.39220.066*
H6C0.35810.86550.45620.066*
C70.38930 (7)0.52140 (18)0.24327 (8)0.0237 (3)
H7A0.35500.55550.19600.028*
H7B0.43330.57680.22960.028*
C80.39867 (7)0.32317 (18)0.23944 (9)0.0251 (3)
H8A0.43670.28820.28140.030*
H8B0.35630.26530.25770.030*
C90.41447 (8)0.2637 (2)0.14602 (9)0.0295 (3)
H9A0.37430.28950.10570.035*
H9B0.45360.33240.12570.035*
C100.43166 (9)0.0710 (2)0.13864 (10)0.0362 (4)
H10A0.47080.04330.17920.054*
H10B0.44330.04440.07780.054*
H10C0.39190.00140.15420.054*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0158 (5)0.0300 (5)0.0263 (5)0.0055 (4)0.0038 (4)0.0070 (4)
O20.0219 (5)0.0330 (5)0.0233 (5)0.0069 (4)0.0026 (4)0.0092 (4)
O30.0184 (5)0.0384 (6)0.0309 (6)0.0024 (4)0.0084 (4)0.0086 (4)
N10.0140 (5)0.0235 (6)0.0194 (6)0.0019 (4)0.0039 (4)0.0042 (4)
N20.0128 (5)0.0286 (6)0.0237 (6)0.0060 (5)0.0021 (4)0.0050 (5)
C10.0148 (6)0.0201 (6)0.0179 (6)0.0002 (5)0.0002 (5)0.0002 (5)
C20.0161 (6)0.0200 (6)0.0201 (6)0.0011 (5)0.0012 (5)0.0006 (5)
C30.0165 (6)0.0219 (6)0.0209 (6)0.0001 (5)0.0025 (5)0.0005 (5)
C40.0159 (6)0.0223 (6)0.0187 (6)0.0015 (5)0.0028 (5)0.0044 (5)
C50.0271 (7)0.0232 (7)0.0314 (8)0.0025 (6)0.0083 (6)0.0070 (6)
C60.0592 (11)0.0287 (8)0.0438 (10)0.0079 (8)0.0087 (8)0.0040 (7)
C70.0215 (7)0.0309 (7)0.0185 (6)0.0037 (6)0.0014 (5)0.0038 (5)
C80.0236 (7)0.0318 (7)0.0196 (7)0.0042 (6)0.0012 (5)0.0006 (6)
C90.0304 (8)0.0358 (8)0.0222 (7)0.0036 (7)0.0010 (6)0.0013 (6)
C100.0400 (9)0.0391 (9)0.0293 (8)0.0026 (7)0.0004 (7)0.0060 (6)
Geometric parameters (Å, º) top
O1—C11.2253 (15)C6—H6A0.980
O2—C21.2201 (15)C6—H6B0.980
O3—C31.2129 (16)C6—H6C0.980
N1—H1N0.882 (19)C7—H7A0.990
N1—C11.3762 (16)C7—H7B0.990
N1—C21.3842 (16)C7—C81.536 (2)
N2—H2N0.883 (16)C8—H8A0.990
N2—C21.3727 (17)C8—H8B0.990
N2—C31.3869 (17)C8—C91.5300 (18)
C1—C41.5212 (18)C9—H9A0.990
C3—C41.5249 (17)C9—H9B0.990
C4—C51.5526 (18)C9—C101.524 (2)
C4—C71.5560 (18)C10—H10A0.980
C5—H5A0.990C10—H10B0.980
C5—H5B0.990C10—H10C0.980
C5—C61.523 (2)
H1N—N1—C1117.5 (11)C5—C6—H6C109.5
H1N—N1—C2116.2 (11)H6A—C6—H6B109.5
C1—N1—C2125.81 (11)H6A—C6—H6C109.5
H2N—N2—C2116.7 (10)H6B—C6—H6C109.5
H2N—N2—C3116.7 (10)C4—C7—H7A108.2
C2—N2—C3126.52 (11)C4—C7—H7B108.2
O1—C1—N1119.84 (12)C4—C7—C8116.23 (11)
O1—C1—C4121.74 (11)H7A—C7—H7B107.4
N1—C1—C4118.40 (11)H7A—C7—C8108.2
O2—C2—N1120.86 (12)H7B—C7—C8108.2
O2—C2—N2122.65 (11)C7—C8—H8A109.4
N1—C2—N2116.49 (11)C7—C8—H8B109.4
O3—C3—N2120.19 (12)C7—C8—C9111.15 (11)
O3—C3—C4122.06 (11)H8A—C8—H8B108.0
N2—C3—C4117.75 (11)H8A—C8—C9109.4
C1—C4—C3114.35 (10)H8B—C8—C9109.4
C1—C4—C5109.21 (11)C8—C9—H9A108.7
C1—C4—C7108.50 (10)C8—C9—H9B108.7
C3—C4—C5108.45 (10)C8—C9—C10114.38 (12)
C3—C4—C7107.10 (11)H9A—C9—H9B107.6
C5—C4—C7109.12 (11)H9A—C9—C10108.7
C4—C5—H5A108.6H9B—C9—C10108.7
C4—C5—H5B108.6C9—C10—H10A109.5
C4—C5—C6114.50 (12)C9—C10—H10B109.5
H5A—C5—H5B107.6C9—C10—H10C109.5
H5A—C5—C6108.6H10A—C10—H10B109.5
H5B—C5—C6108.6H10A—C10—H10C109.5
C5—C6—H6A109.5H10B—C10—H10C109.5
C5—C6—H6B109.5
C2—N1—C1—O1172.55 (12)O3—C3—C4—C1174.50 (12)
C2—N1—C1—C49.21 (18)O3—C3—C4—C552.38 (16)
C3—N2—C2—O2179.71 (12)O3—C3—C4—C765.26 (16)
C3—N2—C2—N10.05 (19)N2—C3—C4—C15.71 (16)
C1—N1—C2—O2175.46 (12)N2—C3—C4—C5127.83 (12)
C1—N1—C2—N24.30 (18)N2—C3—C4—C7114.53 (12)
C2—N2—C3—O3178.94 (13)C1—C4—C5—C668.15 (15)
C2—N2—C3—C41.27 (19)C3—C4—C5—C657.05 (16)
O1—C1—C4—C3172.44 (12)C7—C4—C5—C6173.39 (12)
O1—C1—C4—C550.74 (16)C1—C4—C7—C861.94 (14)
O1—C1—C4—C768.10 (15)C3—C4—C7—C861.97 (14)
N1—C1—C4—C39.35 (16)C5—C4—C7—C8179.17 (11)
N1—C1—C4—C5131.05 (12)C4—C7—C8—C9174.37 (11)
N1—C1—C4—C7110.10 (12)C7—C8—C9—C10174.09 (12)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1N···O1i0.882 (19)2.048 (19)2.9251 (17)172.7 (15)
N2—H2N···O2ii0.883 (16)1.977 (16)2.8530 (15)171.2 (15)
C5—H5B···O3iii0.992.493.3341 (19)143
Symmetry codes: (i) x+1, y+1, z+1; (ii) x+1/2, y+1/2, z+1; (iii) x+1/2, y+1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaC10H16N2O3
Mr212.25
Crystal system, space groupMonoclinic, C2/c
Temperature (K)150
a, b, c (Å)19.519 (4), 7.6868 (15), 15.117 (3)
β (°) 92.77 (3)
V3)2265.5 (8)
Z8
Radiation typeMo Kα
µ (mm1)0.09
Crystal size (mm)0.37 × 0.35 × 0.13
Data collection
DiffractometerNonius KappaCCD
Absorption correctionMulti-scan
(SADABS; Sheldrick, 2003)
Tmin, Tmax0.917, 0.988
No. of measured, independent and
observed [I > 2σ(I)] reflections
12332, 2585, 1958
Rint0.034
(sin θ/λ)max1)0.649
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.039, 0.108, 1.08
No. of reflections2585
No. of parameters146
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.28, 0.20

Computer programs: COLLECT (Nonius, 1998), EVALCCD (Duisenberg et al., 2003), DIAMOND (Brandenburg & Putz, 2004) and Mercury (Bruno et al., 2002), SHELXTL (Sheldrick, 2001) and local programs.

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1N···O1i0.882 (19)2.048 (19)2.9251 (17)172.7 (15)
N2—H2N···O2ii0.883 (16)1.977 (16)2.8530 (15)171.2 (15)
Symmetry codes: (i) x+1, y+1, z+1; (ii) x+1/2, y+1/2, z+1.
 

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