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organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Volume 67| Part 12| December 2011| Page o3357
https://doi.org/10.1107/S1600536811047532

A monoclinic polymorph of theophylline

Shuo Zhanga* and Andreas Fischerb

aDivision of Transport Phenomena, School of Chemical Science and Engineering, Royal Institute of Technology (KTH), 100 44 Stockholm, Sweden, and bInorganic Chemistry, School of Chemical Science and Engineering, Royal Institute of Technology (KTH), 100 44 Stockholm, Sweden
*Correspondence e-mail: shuoz@kth.se

(Received 20 October 2011; accepted 9 November 2011; online 19 November 2011)

A monoclinic polymorph of theophylline, C7H8N4O2, has been obtained from a chloro­form/methanol mixture by evaporation under ambient conditions. The new polymorph crystallizes with two mol­ecules in the asymmetric unit. The structure features inter­molecular N—H⋯O hydrogen bonds, resulting in the formation of dimers between two crystallographically different mol­ecules; each mol­ecule acts as both donor and acceptor.

Related literature

For the ortho­rhom­bic polymorph of anhydrous theophylline, see: Ebisuzaki et al. (1997[Ebisuzaki, Y., Boyle, P. D. & Smith, J. A. (1997). Acta Cryst. C53, 777-779.]).

[Scheme 1]

Experimental

Crystal data

  • C7H8N4O2

  • Mr = 180.17

  • Monoclinic, P 21 /c

  • a = 7.8935 (6) Å

  • b = 12.9087 (7) Å

  • c = 15.9055 (8) Å

  • β = 104.214 (5)°

  • V = 1571.07 (17) Å3

  • Z = 8

  • Mo Kα radiation

  • μ = 0.12 mm−1

  • T = 299 K

  • 0.35 × 0.29 × 0.04 mm
Data collection

  • Bruker–Nonius KappaCCD diffractometer

  • Absorption correction: multi-scan (SADABS; Sheldrick, 2003[Sheldrick, G. M. (2003). SADABS. University of Göttingen, Germany.]) Tmin = 0.863, Tmax = 0.995

  • 19027 measured reflections

  • 3074 independent reflections

  • 1972 reflections with I > 2σ(I)

  • Rint = 0.058
Refinement

  • R[F2 > 2σ(F2)] = 0.048

  • wR(F2) = 0.129

  • S = 1.05

  • 3074 reflections

  • 239 parameters

  • H-atom parameters constrained

  • Δρmax = 0.22 e Å−3

  • Δρmin = −0.24 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A D⋯A D—H⋯A
N4—H4⋯O3i 0.86 1.92 2.753 (2) 163
N8—H8⋯O1i 0.86 1.94 2.782 (2) 165
Symmetry code: (i) -x, -y, -z+1.

Data collection: COLLECT (Nonius, 1998[Nonius (1998). COLLECT. Nonius BV, Delft, The Netherlands.]); cell refinement: DIRAX (Duisenberg, 1992[Duisenberg, A. J. M. (1992). J. Appl. Cryst. 25, 92-96.]); data reduction: EVALCCD (Duisenberg et al., 2003[Duisenberg, A. J. M., Kroon-Batenburg, L. M. J. & Schreurs, A. M. M. (2003). J. Appl. Cryst. 36, 220-229.]); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: DIAMOND (Brandenburg, 2007[Brandenburg, K. (2007). DIAMOND. Crystal Impact GbR, Bonn, Germany.]); software used to prepare material for publication: publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).

Supporting information

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S1600536811047532/wn2455sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536811047532/wn2455Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S1600536811047532/wn2455Isup3.cml

checkCIF report


Comment top

Theophylline,1,3-dimethyl-7H-purine-2,6-dione, is an FDA-approved compound for the treatment of respiratory diseases such as asthma, as are other related compounds, such as caffeine and theobromine.

Thus far, only one crystal structure of anhydrous theophylline has been reported (Ebisuzaki et al., 1997). This orthorhombic structure has one molecule per asymmetric unit and is characterized by N—H···N hydrogen bonds, yielding infinite chains.

The polymorph of theophylline in this work was found during a solubility study using a 4:1 mixture ofchloroform and methanol as solvent. This monoclinic polymorph has been found to be thermodynamically stable at room temperature. Solubility data and a discussion of thermodynamic stability relationships will be presented elsewhere. (Zhang & Rasmuson, manuscript in preparation).

The title compound features two molecules in the asymmetric unit (Fig. 1). They are almost coplanar with a dihedral angle of 5.31 (3)°. Each molecule acts as N—H···O bond donor and acceptor, yielding dimers of two crystallographically different molecules (Fig. 2).

The major difference between the structures of the two polymorphs is their hydrogen bonding pattern.

Related literature top

For the orthorhombic polymorph of anhydrous theophylline, see: Ebisuzaki et al. (1997).

Experimental top

Commercial theophylline was dissolved in a mixture of chloroform and methanol (ratio 4:1 v/v). Evaporation at ambient temperature and pressure over a period of five weeks yielded the title compound. Powder X-ray diffraction confirmed that the bulk material was identical with the single-crystal from which the crystal structure was obtained.

Refinement top

H atoms were placed at calculated positions and refined as riding, with N—H = 0.86 Å, C(methyl)—H = 0.96 Å and Csp2—H = 0.93 Å. Uiso(H) = xUeq(C,N), where x = 1.5 for methyl H and 1.2 for all other H atoms.

Structure description top

Theophylline,1,3-dimethyl-7H-purine-2,6-dione, is an FDA-approved compound for the treatment of respiratory diseases such as asthma, as are other related compounds, such as caffeine and theobromine.

Thus far, only one crystal structure of anhydrous theophylline has been reported (Ebisuzaki et al., 1997). This orthorhombic structure has one molecule per asymmetric unit and is characterized by N—H···N hydrogen bonds, yielding infinite chains.

The polymorph of theophylline in this work was found during a solubility study using a 4:1 mixture ofchloroform and methanol as solvent. This monoclinic polymorph has been found to be thermodynamically stable at room temperature. Solubility data and a discussion of thermodynamic stability relationships will be presented elsewhere. (Zhang & Rasmuson, manuscript in preparation).

The title compound features two molecules in the asymmetric unit (Fig. 1). They are almost coplanar with a dihedral angle of 5.31 (3)°. Each molecule acts as N—H···O bond donor and acceptor, yielding dimers of two crystallographically different molecules (Fig. 2).

The major difference between the structures of the two polymorphs is their hydrogen bonding pattern.

For the orthorhombic polymorph of anhydrous theophylline, see: Ebisuzaki et al. (1997).

Computing details top

Data collection: COLLECT (Nonius, 1998); cell refinement: DIRAX (Duisenberg, 1992); data reduction: EVALCCD (Duisenberg et al., 2003); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2007); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top
[Figure 1] Fig. 1. The asymmetric unit of the title compound. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms are shown as spheres of arbitrary radius.
[Figure 2] Fig. 2. The hydrogen bonding pattern in the title compound, yielding dimers. Hydrogen bonds are indicated as dashed lines.
1,3-dimethyl-7H-purine-2,6-dione top
Crystal data top
C7H8N4O2F(000) = 752
Mr = 180.17Dx = 1.523 Mg m−3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 82 reflections
a = 7.8935 (6) Åθ = 4.2–20.8°
b = 12.9087 (7) ŵ = 0.12 mm−1
c = 15.9055 (8) ÅT = 299 K
β = 104.214 (5)°Plate, colourless
V = 1571.07 (17) Å30.35 × 0.29 × 0.04 mm
Z = 8
Data collection top
Bruker–Nonius KappaCCD
diffractometer		1972 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.058
ω scansθmax = 26.0°, θmin = 4.5°
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)		h = −9→8
Tmin = 0.863, Tmax = 0.995k = −15→15
19027 measured reflectionsl = −19→19
3074 independent reflections
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)] = 0.048H-atom parameters constrained
wR(F2) = 0.129 w = 1/[σ2(Fo2) + (0.0593P)2 + 0.4941P]
where P = (Fo2 + 2Fc2)/3
S = 1.05(Δ/σ)max < 0.001
3074 reflectionsΔρmax = 0.22 e Å−3
239 parametersΔρmin = −0.24 e Å−3
0 restraints
Crystal data top
C7H8N4O2V = 1571.07 (17) Å3
Mr = 180.17Z = 8
Monoclinic, P21/cMo Kα radiation
a = 7.8935 (6) ŵ = 0.12 mm−1
b = 12.9087 (7) ÅT = 299 K
c = 15.9055 (8) Å0.35 × 0.29 × 0.04 mm
β = 104.214 (5)°
Data collection top
Bruker–Nonius KappaCCD
diffractometer		3074 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)		1972 reflections with I > 2σ(I)
Tmin = 0.863, Tmax = 0.995Rint = 0.058
19027 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0480 restraints
wR(F2) = 0.129H-atom parameters constrained
S = 1.05Δρmax = 0.22 e Å−3
3074 reflectionsΔρmin = −0.24 e Å−3
239 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.

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 (Å2) top
xyzUiso*/Ueq
C10.3056 (3)0.02115 (17)0.09461 (14)0.0352 (5)
C20.4877 (3)0.17786 (17)0.09060 (14)0.0342 (5)
C30.3328 (3)0.09963 (17)−0.04057 (13)0.0316 (5)
C40.2672 (3)0.02566 (17)0.00340 (14)0.0336 (5)
C50.1763 (3)0.0045 (2)−0.13534 (15)0.0435 (6)
C60.4624 (4)0.1056 (2)0.22819 (15)0.0554 (7)
C70.5185 (3)0.2516 (2)−0.04623 (16)0.0489 (6)
C80.0635 (3)0.28631 (17)1.02459 (14)0.0337 (5)
C90.2209 (3)0.45280 (17)1.02194 (14)0.0351 (5)
C100.0752 (3)0.37253 (17)0.89022 (13)0.0324 (5)
C110.0220 (3)0.29279 (16)0.93328 (13)0.0314 (5)
C12−0.0732 (3)0.27496 (19)0.79473 (14)0.0425 (6)
C130.2196 (3)0.3724 (2)1.15919 (14)0.0475 (6)
C140.2368 (3)0.53625 (19)0.88634 (16)0.0471 (6)
N10.4160 (2)0.10126 (14)0.13328 (11)0.0361 (5)
N20.4434 (2)0.17564 (14)0.00173 (11)0.0346 (4)
N30.2779 (3)0.08774 (15)−0.12768 (12)0.0418 (5)
N40.1653 (2)−0.03563 (15)−0.05995 (12)0.0391 (5)
N50.1646 (2)0.36962 (14)1.06438 (11)0.0345 (4)
N60.1742 (2)0.45278 (14)0.93298 (12)0.0366 (5)
N70.0172 (3)0.36232 (15)0.80311 (12)0.0433 (5)
N8−0.0753 (2)0.23019 (15)0.86970 (11)0.0366 (5)
O10.2529 (2)−0.04282 (13)0.13937 (10)0.0497 (5)
O20.5851 (2)0.24386 (13)0.13070 (10)0.0484 (4)
O30.0208 (2)0.21730 (13)1.06858 (10)0.0496 (5)
O40.3076 (2)0.52232 (13)1.06289 (11)0.0514 (5)
H50.1181−0.0232−0.18860.052*
H6A0.55440.15520.24750.083*
H6B0.50130.03860.25120.083*
H6C0.36190.12590.24810.083*
H7A0.49130.3201−0.03000.073*
H7B0.47070.2419−0.10730.073*
H7C0.64300.2429−0.03300.073*
H12−0.13010.24740.74120.051*
H13A0.34480.36911.17740.071*
H13B0.17040.31431.18250.071*
H13C0.17970.43551.17980.071*
H14A0.20420.60190.90610.071*
H14B0.18560.52930.82530.071*
H14C0.36170.53240.89700.071*
H40.1062−0.0893−0.05230.047*
H8−0.12720.17350.87690.044*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0348 (11)0.0294 (13)0.0408 (12)−0.0032 (10)0.0079 (10)0.0011 (10)
C20.0323 (12)0.0308 (12)0.0378 (12)−0.0009 (10)0.0052 (9)−0.0005 (10)
C30.0316 (11)0.0286 (12)0.0336 (11)0.0031 (9)0.0061 (9)−0.0018 (9)
C40.0315 (11)0.0301 (13)0.0378 (12)−0.0008 (9)0.0059 (9)−0.0033 (10)
C50.0490 (14)0.0433 (15)0.0358 (13)−0.0034 (12)0.0054 (10)−0.0076 (11)
C60.0696 (18)0.0563 (18)0.0351 (13)−0.0173 (14)0.0034 (12)0.0011 (12)
C70.0568 (15)0.0423 (15)0.0501 (14)−0.0130 (12)0.0182 (12)0.0037 (12)
C80.0329 (11)0.0294 (12)0.0391 (12)−0.0022 (9)0.0093 (9)−0.0004 (10)
C90.0343 (11)0.0301 (13)0.0412 (13)−0.0035 (10)0.0098 (10)−0.0047 (10)
C100.0298 (11)0.0312 (12)0.0347 (11)0.0018 (9)0.0049 (9)0.0014 (10)
C110.0309 (11)0.0268 (12)0.0348 (12)−0.0019 (9)0.0046 (9)−0.0016 (9)
C120.0443 (13)0.0419 (15)0.0354 (13)−0.0028 (11)−0.0018 (10)−0.0015 (11)
C130.0569 (15)0.0482 (16)0.0349 (12)−0.0065 (13)0.0063 (11)−0.0055 (11)
C140.0518 (15)0.0378 (15)0.0526 (15)−0.0097 (11)0.0147 (12)0.0067 (11)
N10.0400 (10)0.0336 (11)0.0318 (10)−0.0063 (8)0.0030 (8)−0.0002 (8)
N20.0377 (10)0.0297 (10)0.0356 (10)−0.0049 (8)0.0074 (8)0.0007 (8)
N30.0493 (11)0.0394 (12)0.0359 (10)−0.0039 (9)0.0088 (9)−0.0042 (9)
N40.0390 (10)0.0334 (11)0.0428 (11)−0.0084 (8)0.0060 (9)−0.0048 (9)
N50.0386 (10)0.0321 (11)0.0321 (9)−0.0047 (8)0.0073 (8)−0.0038 (8)
N60.0413 (11)0.0280 (10)0.0404 (11)−0.0055 (8)0.0096 (8)0.0020 (8)
N70.0495 (12)0.0381 (12)0.0377 (11)−0.0044 (10)0.0021 (9)0.0034 (9)
N80.0385 (10)0.0301 (11)0.0384 (10)−0.0073 (8)0.0040 (8)−0.0013 (8)
O10.0596 (11)0.0450 (11)0.0429 (10)−0.0183 (8)0.0099 (8)0.0047 (8)
O20.0516 (10)0.0408 (10)0.0483 (10)−0.0171 (8)0.0034 (8)−0.0057 (8)
O30.0661 (11)0.0410 (10)0.0410 (9)−0.0177 (9)0.0116 (8)0.0023 (8)
O40.0599 (11)0.0405 (10)0.0518 (10)−0.0173 (9)0.0098 (8)−0.0104 (8)
Geometric parameters (Å, º) top
C1—O11.228 (3)C10—N61.373 (3)
C1—N11.394 (3)C11—N81.373 (3)
C1—C41.409 (3)C12—N71.324 (3)
C2—O21.218 (3)C12—N81.329 (3)
C2—N21.370 (3)C13—N51.464 (3)
C2—N11.396 (3)C14—N61.461 (3)
C3—N31.355 (3)C5—H50.9300
C3—C41.359 (3)C6—H6A0.9600
C3—N21.374 (3)C6—H6B0.9600
C4—N41.375 (3)C6—H6C0.9600
C5—N41.328 (3)C7—H7A0.9600
C5—N31.329 (3)C7—H7B0.9600
C6—N11.465 (3)C7—H7C0.9600
C7—N21.455 (3)C12—H120.9300
C8—O31.230 (3)C13—H13A0.9600
C8—N51.395 (3)C13—H13B0.9600
C8—C111.411 (3)C13—H13C0.9600
C9—O41.216 (3)C14—H14A0.9600
C9—N61.372 (3)C14—H14B0.9600
C9—N51.398 (3)C14—H14C0.9600
C10—N71.355 (3)N4—H40.8600
C10—C111.359 (3)N8—H80.8600
O1—C1—N1120.46 (19)C9—N6—C10119.16 (18)
O1—C1—C4127.4 (2)C9—N6—C14118.99 (19)
N1—C1—C4112.14 (19)C10—N6—C14121.81 (19)
O2—C2—N2121.5 (2)C12—N7—C10102.95 (19)
O2—C2—N1121.4 (2)C12—N8—C11106.07 (19)
N2—C2—N1117.11 (19)N4—C5—H5123.1
N3—C3—C4112.32 (19)N3—C5—H5123.1
N3—C3—N2125.9 (2)N1—C6—H6A109.5
C4—C3—N2121.75 (19)N1—C6—H6B109.5
C3—C4—N4104.81 (18)H6A—C6—H6B109.5
C3—C4—C1123.1 (2)N1—C6—H6C109.5
N4—C4—C1132.1 (2)H6A—C6—H6C109.5
N4—C5—N3113.8 (2)H6B—C6—H6C109.5
O3—C8—N5120.43 (19)N2—C7—H7A109.5
O3—C8—C11127.0 (2)N2—C7—H7B109.5
N5—C8—C11112.55 (19)H7A—C7—H7B109.5
O4—C9—N6121.7 (2)N2—C7—H7C109.5
O4—C9—N5120.8 (2)H7A—C7—H7C109.5
N6—C9—N5117.47 (19)H7B—C7—H7C109.5
N7—C10—C11111.92 (19)N7—C12—H12123.0
N7—C10—N6126.0 (2)N8—C12—H12123.0
C11—C10—N6122.04 (19)N5—C13—H13A109.5
C10—C11—N8105.13 (18)N5—C13—H13B109.5
C10—C11—C8122.8 (2)H13A—C13—H13B109.5
N8—C11—C8132.1 (2)N5—C13—H13C109.5
N7—C12—N8113.9 (2)H13A—C13—H13C109.5
C1—N1—C2126.52 (17)H13B—C13—H13C109.5
C1—N1—C6117.04 (18)N6—C14—H14A109.5
C2—N1—C6116.44 (18)N6—C14—H14B109.5
C2—N2—C3119.36 (18)H14A—C14—H14B109.5
C2—N2—C7119.55 (19)N6—C14—H14C109.5
C3—N2—C7121.06 (18)H14A—C14—H14C109.5
C5—N3—C3102.70 (19)H14B—C14—H14C109.5
C5—N4—C4106.34 (19)C5—N4—H4126.8
C8—N5—C9125.98 (18)C4—N4—H4126.8
C8—N5—C13118.55 (18)C12—N8—H8127.0
C9—N5—C13115.47 (18)C11—N8—H8127.0
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N4—H4···O3i0.861.922.753 (2)163
N8—H8···O1i0.861.942.782 (2)165
Symmetry code: (i) −x, −y, −z+1.

Experimental details

Crystal data
Chemical formulaC7H8N4O2
Mr180.17
Crystal system, space groupMonoclinic, P21/c
Temperature (K)299
a, b, c (Å)7.8935 (6), 12.9087 (7), 15.9055 (8)
β (°) 104.214 (5)
V (Å3)1571.07 (17)
Z8
Radiation typeMo Kα
µ (mm−1)0.12
Crystal size (mm)0.35 × 0.29 × 0.04
Data collection
DiffractometerBruker–Nonius KappaCCD
Absorption correctionMulti-scan
(SADABS; Sheldrick, 2003)
Tmin, Tmax0.863, 0.995
No. of measured, independent and
observed [I > 2σ(I)] reflections		19027, 3074, 1972
Rint0.058
(sin θ/λ)max (Å−1)0.617
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.048, 0.129, 1.05
No. of reflections3074
No. of parameters239
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å−3)0.22, −0.24

Computer programs: COLLECT (Nonius, 1998), DIRAX (Duisenberg, 1992), EVALCCD (Duisenberg et al., 2003), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 2007), publCIF (Westrip, 2010).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N4—H4···O3i0.861.922.753 (2)163
N8—H8···O1i0.861.942.782 (2)165
Symmetry code: (i) −x, −y, −z+1.
 

Acknowledgements

The Swedish Research Council (VR) is acknowledged for providing funding for the single-crystal diffractometer.

References

First citationBrandenburg, K. (2007). DIAMOND. Crystal Impact GbR, Bonn, Germany.  Google Scholar
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ISSN: 2056-9890
Volume 67| Part 12| December 2011| Page o3357
https://doi.org/10.1107/S1600536811047532
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