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Acta Cryst. (2007). E63, o4147    [ doi:10.1107/S1600536807045448 ]

A second C2/c polymorph of butobarbitone

G. S. Nichol and W. Clegg

Abstract top

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.

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.

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
C10H16N2O3F000 = 912
Mr = 212.25Dx = 1.245 Mg m−3
Monoclinic, C2/cMo Kα radiation
λ = 0.71073 Å
Hall symbol: -C 2ycCell parameters from 6280 reflections
a = 19.519 (4) Åθ = 2.5–27.5º
b = 7.6868 (15) ŵ = 0.09 mm−1
c = 15.117 (3) ÅT = 150 (2) K
β = 92.77 (3)ºBlock, 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)
Monochromator: graphiteRint = 0.034
T = 150(2) Kθmax = 27.5º
φ and ω scansθmin = 4.8º
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)		h = −25→25
Tmin = 0.917, Tmax = 0.988k = −9→9
12332 measured reflectionsl = −18→19
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.039H atoms treated by a mixture of
independent and constrained refinement
wR(F2) = 0.108  w = 1/[σ2(Fo2) + (0.0526P)2 + 1.0348P]
where P = (Fo2 + 2Fc2)/3
S = 1.08(Δ/σ)max < 0.001
2585 reflectionsΔρmax = 0.28 e Å−3
146 parametersΔρmin = −0.20 e Å−3
Primary atom site location: structure-invariant direct methodsExtinction correction: none
Crystal data top
C10H16N2O3V = 2265.5 (8) Å3
Mr = 212.25Z = 8
Monoclinic, C2/cMo Kα
a = 19.519 (4) ŵ = 0.09 mm−1
b = 7.6868 (15) ÅT = 150 (2) K
c = 15.117 (3) Å0.37 × 0.35 × 0.13 mm
β = 92.77 (3)º
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)] = 0.039146 parameters
wR(F2) = 0.108H atoms treated by a mixture of
independent and constrained refinement
S = 1.08Δρmax = 0.28 e Å−3
2585 reflectionsΔρmin = −0.20 e Å−3
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, °) 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—C4−9.21 (18)O3—C3—C4—C552.38 (16)
C3—N2—C2—O2179.71 (12)O3—C3—C4—C7−65.26 (16)
C3—N2—C2—N1−0.05 (19)N2—C3—C4—C1−5.71 (16)
C1—N1—C2—O2−175.46 (12)N2—C3—C4—C5−127.83 (12)
C1—N1—C2—N24.30 (18)N2—C3—C4—C7114.53 (12)
C2—N2—C3—O3−178.94 (13)C1—C4—C5—C6−68.15 (15)
C2—N2—C3—C41.27 (19)C3—C4—C5—C657.05 (16)
O1—C1—C4—C3−172.44 (12)C7—C4—C5—C6173.39 (12)
O1—C1—C4—C5−50.74 (16)C1—C4—C7—C861.94 (14)
O1—C1—C4—C768.10 (15)C3—C4—C7—C8−61.97 (14)
N1—C1—C4—C39.35 (16)C5—C4—C7—C8−179.17 (11)
N1—C1—C4—C5131.05 (12)C4—C7—C8—C9174.37 (11)
N1—C1—C4—C7−110.10 (12)C7—C8—C9—C10174.09 (12)
Hydrogen-bond geometry (Å, °) 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.
Hydrogen-bond geometry (Å, °) 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.
Acknowledgements top

The authors thank Professor Roger Griffin, Newcastle University, for supplying the butobarbitone used in our research.

references
References top

Bideau, J.-P. (1971). C. R. Acad. Sc. Paris. Ser. C. 272, 757–760.

Brandenburg, K. & Putz, H. (2004). DIAMOND. Version 3. University of Bonn, Germany.

Bruno, I. J., Cole, J. C., Edgington, P. R., Kessler, M., Macrae, C. F., McCabe, P., Pearson, J. & Taylor, R. (2002). Acta Cryst. B58, 389–397.

Duisenberg, A. J. M., Kroon-Batenburg, L. M. J. & Schreurs, A. M. M. (2003). J. Appl. Cryst. 36, 220–229.

Nichol, G. S. & Clegg, W. (2005). Acta Cryst. C61, o297–o299.

Nonius (1998). COLLECT. Nonius BV, Delft, The Netherlands.

Sheldrick, G. M. (2001). SHELXTL. Version 6. Bruker AXS Inc., Madison, Wisconsin, USA.

Sheldrick, G. M. (2003). SADABS. University of Göttingen, Germany.