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

Journal logoSTRUCTURAL
CHEMISTRY
ISSN: 2053-2296

Anhydrous guanine: a synchrotron study

aSchool of Natural Sciences (Chemistry), Newcastle University, Newcastle upon Tyne NE1 7RU, England
*Correspondence e-mail: w.clegg@ncl.ac.uk

(Received 5 July 2006; accepted 6 July 2006; online 29 July 2006)

Very small crystals of anhydrous guanine (systematic name: 2-amino-1,7-dihydro-6H-purin-6-one), C5H5N5O, were obtained from an attempted solvothermal synthesis of a potassium complex. Data were collected at 120 K using a synchrotron radiation source. There is one essentially planar mol­ecule in the asymmetric unit. Mol­ecules are linked to each other by N—H⋯N and N—H⋯O hydrogen bonds to form sheets, between which there are ππ stacking inter­actions. This crystal structure determination demonstrates conclusively that, in the absence of any solvent or other mol­ecules, guanine exists as the amino–keto tautomer in the solid state, with H atoms attached to N1 and N7 (purine numbering), unlike its monohydrate, which has H atoms on N1 and N9.

Comment

In view of the importance of the nucleobases adenine, cytosine, guanine, thymine and uracil as components of the nucleic acids DNA and RNA (Blackburn & Gait, 1996[Blackburn, G. M. & Gait, M. J. (1996). Nucleic Acids in Chemistry and Biology, 2nd ed. Oxford University Press.]), and the structural characterization of many of their derivatives, it is surprising that the crystal structures of anhydrous adenine and guanine have not yet been reported, although the structures of hydrates are known for both (Tret'yak et al., 1987[Tret'yak, S. M., Mitkevich, V. V. & Sukhodub, L. F. (1987). Kristallografiya, 32, 1268-1271. (In Russian.)]; Thewalt et al., 1971[Thewalt, U., Bugg, C. E. & Marsh, R. E. (1971). Acta Cryst. B27, 2358-2363.]). By contrast, the structures of anhydrous cytosine (Barker & Marsh, 1964[Barker, D. L. & Marsh, R. E. (1964). Acta Cryst. 17, 1581-1587.]; McClure & Craven, 1973[McClure, R. J. & Craven, B. M. (1973). Acta Cryst. B29, 1234-1238.]), thymine (Ozeki et al., 1969[Ozeki, K., Sakabe, N. & Tanaka, J. (1969). Acta Cryst. B25, 1038-1045.]; Portalone et al., 1999[Portalone, G., Bencivenni, L., Colapietro, M., Pieretti, A. & Ramondo, F. (1999). Acta Chem. Scand. 53, 57-68.]) and uracil (Stewart & Jensen, 1967[Stewart, R. F. & Jensen, L. H. (1967). Acta Cryst. 23, 1102-1105.]) have been known for some time, together with hydrates of cytosine (Jeffrey & Kinoshita, 1963[Jeffrey, G. A. & Kinoshita, Y. (1963). Acta Cryst. 16, 20-28.]; Neidle et al., 1976[Neidle, S., Achari, A. & Rabinovitch, M. (1976). Acta Cryst. B32, 2050-2053.]; Eisenstein, 1988[Eisenstein, M. (1988). Acta Cryst. B44, 412-426.]; McClure & Craven, 1973[McClure, R. J. & Craven, B. M. (1973). Acta Cryst. B29, 1234-1238.]) and thymine (Gerdil, 1961[Gerdil, R. (1961). Acta Cryst. 14, 333-344.]), but not of uracil.

For some time, an area of our research has concentrated on the synthesis and characterization of s-block metal complexes with pyridones and related compounds. As an extension of this work, we are studying the structural chemistry of complexes of nucleobases. Their structural chemistry with transition metals is well known and many complexes have been synthesized and characterized. In contrast, the literature does not contain many structures of s-block metal nucleobase complexes and little information is available on the subject (Gibson et al., 2002[Gibson, A. E., Price, C., Clegg, W. & Houlton, A. (2002). J. Chem. Soc. Dalton Trans. pp. 131-133.]), despite their use as reagents (often as sodium or potassium derivatives) to permit further reactions with transition metals.

[Scheme 1]

The crystal structure of guanine is of great importance, as this purine is present in both DNA and RNA (Lippert et al., 2000[Lippert, B. (2000). Coord. Chem. Rev. 200-202, 487-516.]). Guanine nucleotides are involved in inter­mediary metabolism and can also be found in animal tissues. Guanine, like other related bases, can exist in a tautomeric keto–enol equilibrium. It is known that the predominant form of guanine, thymine and uracil is the keto form, and the predominant form for cytosine and adenine is the amino form (Saenger, 1984[Saenger, W. (1984). Principles of Nucleic Acid Structure. New York: Springer.]). A particular inter­est in the crystal structure of anhydrous guanine is to see which tautomeric form occurs and which two of the four ring N atoms are protonated. In the literature, the favoured positions of these two H atoms have often been found to be at N1 and N9, as for guanine monohydrate (Thewalt et al., 1971[Thewalt, U., Bugg, C. E. & Marsh, R. E. (1971). Acta Cryst. B27, 2358-2363.]).

As part of our work, we obtained very small crystals of anhydrous guanine, (I)[link], in an attempted solvothermal synthesis with potassium metal in ethanol. Because of the weak diffraction, data collection was carried out at Station 9.8 of the Synchrotron Radiation Source (SRS) at Daresbury Laboratory, England, through the EPSRC National Crystallography Service.

The asymmetric unit of (I)[link] is shown in Fig. 1[link] and consists of one mol­ecule of guanine. The mol­ecule is essentially planar (r.m.s. deviation of 0.009 Å for all non-H atoms) and, in contrast with guanine monohydrate, the two protonated ring N atoms are found to be N1 and N7. Table 1[link] gives selected bond lengths and angles for the anhydrous structure. The most significant differences from the monohydrate (Thewalt et al., 1971[Thewalt, U., Bugg, C. E. & Marsh, R. E. (1971). Acta Cryst. B27, 2358-2363.]) are the reversal of the N7—C8 and N9—C8 bond lengths and a shortening of C5—C7 in the anhydrous structure: N7—C8 = 1.342 (5) Å in the anhydrate (cf. 1.319 Å in the hydrate), N9—C8 = 1.328 (6) Å (cf. 1.369 Å) and C5—N7 = 1.373 (5) Å (1.405 Å). These differences clearly reflect the different sites of protonation, N7 versus N9. Other bond lengths are very similar in the two structures.

The difference in tautomeric form between the two structures is presumably a consequence of hydrogen bonding in the crystal structures. Fig. 2[link] shows the hydrogen bonding in the crystal structure of anhydrous guanine. Along the b axis, the mol­ecules are linked together to create infinite chains and show a triple hydrogen-bonding motif, ADDDAA (Burrows et al., 1995[Burrows, A. D., Chan, C.-W., Chowdhry, M. M., McGrady, J. E. & Mingos, D. M. P. (1995). Chem. Soc. Rev. pp. 329-339.]), where the donors are N—H and the acceptor atoms are N3, N9 and O6. Geometric details of the hydrogen bonds are given in Table 2[link]. Hydrogen bonds in which atom N7 is the donor and atom O6 the acceptor link these chains together into sheets parallel to (102) (Fig. 3[link]). The spacing between the sheets is 3.263 Å, typical of nucleobase stacking and indicating ππ inter­actions involving offset parallel rings. Guanine monohydrate also forms sheets, but the water mol­ecules are incorporated in the hydrogen bonding and promote the transfer of an H atom from N7 to N9 in order to give favourable hydrogen-bonding inter­actions.

[Figure 1]
Figure 1
The mol­ecular structure of (I)[link], showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
[Figure 2]
Figure 2
The hydrogen bonding (dashed lines) in the crystal structure of (I)[link], viewed perpendicular to the sheet of mol­ecules.
[Figure 3]
Figure 3
An edge-on view, along the b axis, of the stacked planar (102) sheets of hydrogen-bonded mol­ecules.

Experimental

Very small crystals of guanine were obtained from an attempted solvothermal synthesis, using guanine (150 mg) and solid potassium (40 mg) in dry ethanol (10 ml). The mixture was stirred for 1 h and then heated in an autoclave at 523 K for 7 d.

Crystal data
  • C5H5N5O

  • Mr = 151.14

  • Monoclinic, P 21 /c

  • a = 3.5530 (16) Å

  • b = 9.693 (4) Å

  • c = 16.345 (7) Å

  • β = 95.748 (6)°

  • V = 560.1 (4) Å3

  • Z = 4

  • Dx = 1.792 Mg m−3

  • Synchrotron radiation

  • λ = 0.6712 Å

  • μ = 0.14 mm−1

  • T = 120 (2) K

  • Block, colourless

  • 0.01 × 0.01 × 0.01 mm

Data collection
  • Bruker APEX2 CCD area-detector diffractometer

  • Thin-slice ω scans

  • 3444 measured reflections

  • 795 independent reflections

  • 624 reflections with I > 2σ(I)

  • Rint = 0.054

  • θmax = 21.9°

Refinement
  • Refinement on F2

  • R[F2 > 2σ(F2)] = 0.059

  • wR(F2) = 0.183

  • S = 1.15

  • 795 reflections

  • 116 parameters

  • Only H-atom coordinates refined

  • w = 1/[σ2(Fo2) + (0.1065P)2 + 0.537P] where P = (Fo2 + 2Fc2)/3

  • (Δ/σ)max < 0.001

  • Δρmax = 0.34 e Å−3

  • Δρmin = −0.34 e Å−3

  • Extinction correction: SHELXTL (Sheldrick, 2001[Sheldrick, G. M. (2001). SHELXTL. Version 6.10. Bruker AXS Inc., Madison, Wisconsin, USA.])

  • Extinction coefficient: 0.12 (5)

Table 1
Selected geometric parameters (Å, °)

N1—C2 1.372 (5)
N1—C6 1.387 (5)
N2—C2 1.330 (6)
C2—N3 1.330 (5)
N3—C4 1.356 (5)
C4—C5 1.378 (6)
C4—N9 1.364 (5)
C5—C6 1.412 (6)
C5—N7 1.373 (5)
O6—C6 1.249 (5)
N7—C8 1.342 (5)
C8—N9 1.328 (6)
C2—N1—C6 124.6 (3)
N1—C2—N2 117.0 (4)
N1—C2—N3 123.3 (4)
N2—C2—N3 119.7 (4)
C2—N3—C4 114.1 (3)
N3—C4—C5 125.2 (4)
N3—C4—N9 124.6 (4)
C5—C4—N9 110.2 (4)
C4—C5—C6 121.0 (4)
C4—C5—N7 106.7 (3)
C6—C5—N7 132.3 (4)
N1—C6—C5 111.8 (3)
N1—C6—O6 120.0 (4)
C5—C6—O6 128.3 (4)
C5—N7—C8 105.2 (4)
N7—C8—N9 114.1 (4)
C4—N9—C8 103.9 (3)

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N1—H1⋯N3i 0.91 (5) 1.97 (5) 2.862 (5) 167 (4)
N2—H2A⋯N9i 0.85 (5) 2.17 (5) 3.006 (5) 173 (4)
N2—H2B⋯O6ii 0.88 (5) 2.03 (5) 2.902 (5) 174 (4)
N7—H7⋯O6iii 1.00 (5) 1.76 (5) 2.742 (5) 165 (4)
Symmetry codes: (i) [-x+1, y-{\script{1\over 2}}, -z+{\script{3\over 2}}]; (ii) [-x+1, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]; (iii) -x, -y, -z+2.

Diffraction from the very small crystals was weak, and even with synchrotron radiation significant intensities were not observed beyond a resolution of 0.9 Å. Nevertheless, these data gave an excellent structural result, albeit with a lower data/parameter ratio than usual. SADABS (Sheldrick, 2003[Sheldrick, G. M. (2003). SADABS. University of Göttingen, Germany.]) was used to correct for the synchrotron beam decay. All H atoms were found in a difference map and their positions were freely refined [C8—H8 = 0.97 (5) Å; N—H distances are given in Table 2[link]], with Uiso(H) = 1.2Ueq(C,N).

Data collection: APEX2 (Bruker, 2004[Bruker (2004). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2004[Bruker (2004). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SIR2002 (Burla et al., 2003[Burla, M. C., Camalli, M., Carrozzini, B., Cascarano, G. L., Giacovazzo, C., Polidori, G. & Spagna, R. (2003). J. Appl. Cryst. 36, 1103.]); program(s) used to refine structure: SHELXTL (Sheldrick, 2001[Sheldrick, G. M. (2001). SHELXTL. Version 6.10. Bruker AXS Inc., Madison, Wisconsin, USA.]); molecular graphics: SHELXTL and DIAMOND (Brandenburg & Putz, 2004[Brandenburg, K. & Putz, H. (2004). DIAMOND. Version 3. University of Bonn, Germany.]); software used to prepare material for publication: SHELXTL and local programs.

Supporting information


Comment top

In view of the importance of the nucleobases adenine, cytosine, guanine, thymine and uracil as components of the nucleic acids DNA and RNA (Blackburn & Gait, 1996), and the structural characterization of many of their derivatives, it is surprising that the crystal structures of anhydrous adenine and guanine have not yet been reported, although the structures of hydrates are known for both (Tret'yak et al., 1987; Thewalt et al., 1971). By contrast, the structures of anhydrous cytosine (Barker & Marsh, 1964; McClure & Craven, 1973), thymine (Ozeki et al., 1969; Portalone et al., 1999) and uracil (Stewart & Jensen, 1967) have been known for some time, together with hydrates of cytosine (Jeffrey & Kinoshita, 1963; Neidle et al., 1976; Eisenstein, 1988; McClure & Craven, 1973) and thymine (Gerdil, 1961), but not of uracil.

For some time, an area of our research has concentrated on the synthesis and characterization of s-block metal complexes with pyridones and related compounds. As an extension of this work, we are studying the structural chemistry of complexes of nucleobases. Their structural chemistry with transition metals is well known and many complexes have been synthesized and characterized. In contrast, the literature does not contain many structures of s-block metal nucleobase complexes and little information is available on the subject (Gibson et al., 2002), despite their use as reagents (often as sodium or potassium derivatives) to permit further reactions with transition metals.

The crystal structure of guanine is of great importance, as this purine is present in both DNA and RNA (Lippert et al., 2000). Guanine nucleotides are involved in intermediary metabolism and can also be found in animal tissues. Guanine, like other related bases, can exist in a tautomeric keto–enol equilibrium. It is known that the predominant form of guanine, thymine and uracil is the keto form, and the predominant form for cytosine and adenine is the amino form (Saenger, 1984). A particular interest in the crystal structure of anhydrous guanine is to see which tautomeric form occurs and which two of the four ring N atoms are protonated. In the literature, the favoured positions of these two H atoms have often been found to be at N1 and N9, as for guanine monohydrate (Thewalt et al., 1971).

As part of our work, we obtained very small crystals of anhydrous guanine, (I), in an attempted solvothermal synthesis with potassium metal in ethanol. Because of the weak diffraction, data collection was carried out at Station 9.8 of the Synchrotron Radiation Source (SRS) at Daresbury Laboratory, England, through the EPSRC National Crystallographic Service.

The asymmetric unit of (I) is shown in Fig. 1 and consists of one molecule of guanine. The molecule is essentially planar (r.m.s. deviation of 0.009 Å for all non-H atoms) and, in contrast with guanine monohydrate, the two protonated ring N atoms are found to be N1 and N7. Table 1 gives selected bond lengths and angles for the anhydrous structure. The most significant differences from the monohydrate (Thewalt et al., 1971) are the reversal of the N7—C8 and N9—C8 bond lengths and a shortening of C5—C7 in the anhydrous structure: N7—C8 = 1.342 (5) Å in the anhydrate (cf. 1.319 Å in the hydrate), N9—C8 = 1.328 (6) Å (cf. 1.369 Å), and C5—N7 = 1.373 (5) Å (1.405 Å). These differences clearly reflect the different sites of protonation, N7 versus N9. Other bond lengths are very similar in the two structures.

The difference in tautomeric form between the two structures is presumably a consequence of hydrogen bonding in the crystal structures. Fig. 2 shows the hydrogen bonding in the crystal structure of anhydrous guanine. Along the b axis, the molecules are linked together to create infinite chains and show a triple hydrogen-bonding motif, ADD···DAA (Burrows et al., 1995), where the donors are N—H and the acceptor atoms are N3, N9 and O6. Geometric details of the hydrogen bonds are given in Table 2. Hydrogen bonds in which atom N7 is the donor and atom O6 the acceptor link these chains together into sheets parallel to (102) (Fig. 3). The spacing between the sheets is 3.263 Å, typical of nucleobase stacking and indicating ππ interactions involving offset parallel rings. Guanine monohydrate also forms sheets, but the water molecules are incorporated in the hydrogen bonding and promote the transfer of an H atom from N7 to N9 in order to give favourable hydrogen-bonding interactions.

Experimental top

Very small crystals of guanine were obtained from an attempted solvothermal synthesis, with guanine (150 mg) and solid potassium (40 mg) in dry ethanol (10 ml). The mixture was stirred for 1 h and then heated in an autoclave at 523 K for 7 d.

Refinement top

Diffraction from the very small crystals was weak, and even with synchrotron radiation significant intensities were not observed beyond a resolution of 0.9 Å. Nevertheless, these data gave an excellent structural result, albeit with a lower data/parameter ratio than usual. SADABS (Sheldrick, 2003) was used to correct for the synchrotron beam decay. All H atoms were found in a difference map and their positions were freely refined [Range of distances with s.u.s?], with Uiso(H) = 1.2Ueq(C,N).

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SIR2002 (Burla et al., 2003); program(s) used to refine structure: SHELXTL (Sheldrick, 2001); molecular graphics: SHELXTL and DIAMOND (Brandenburg & Putz, 2004); software used to prepare material for publication: SHELXTL and local programs.

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability leve and H atoms are shown as small spheres of arbitrary radii.
[Figure 2] Fig. 2. The hydrogen bonding (dashed lines) in the crystal structure of (I), viewed perpendicular to the sheet of molecules.
[Figure 3] Fig. 3. An edge-on view, along the b axis, of the stacked planar (102) sheets of hydrogen-bonded molecules.
2-amino-1,7-dihydro-6H-purin-6-one top
Crystal data top
C5H5N5OF(000) = 312
Mr = 151.14Dx = 1.792 Mg m3
Monoclinic, P21/cSynchrotron radiation, λ = 0.6712 Å
Hall symbol: -P 2ybcCell parameters from 856 reflections
a = 3.5530 (16) Åθ = 2.3–21.5°
b = 9.693 (4) ŵ = 0.14 mm1
c = 16.345 (7) ÅT = 120 K
β = 95.748 (6)°Block, colourless
V = 560.1 (4) Å30.01 × 0.01 × 0.01 mm
Z = 4
Data collection top
Bruker APEX2 CCD area-detector
diffractometer
624 reflections with I > 2σ(I)
Radiation source: Daresbury SRS station 9.8Rint = 0.054
Silicon 111 monochromatorθmax = 21.9°, θmin = 2.3°
thin–slice ω scansh = 33
3444 measured reflectionsk = 1010
795 independent reflectionsl = 1718
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.059Only H-atom coordinates refined
wR(F2) = 0.183 w = 1/[σ2(Fo2) + (0.1065P)2 + 0.537P]
where P = (Fo2 + 2Fc2)/3
S = 1.15(Δ/σ)max < 0.001
795 reflectionsΔρmax = 0.34 e Å3
116 parametersΔρmin = 0.34 e Å3
0 restraintsExtinction correction: SHELXTL (Sheldrick, 2001), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.12 (5)
Crystal data top
C5H5N5OV = 560.1 (4) Å3
Mr = 151.14Z = 4
Monoclinic, P21/cSynchrotron radiation, λ = 0.6712 Å
a = 3.5530 (16) ŵ = 0.14 mm1
b = 9.693 (4) ÅT = 120 K
c = 16.345 (7) Å0.01 × 0.01 × 0.01 mm
β = 95.748 (6)°
Data collection top
Bruker APEX2 CCD area-detector
diffractometer
624 reflections with I > 2σ(I)
3444 measured reflectionsRint = 0.054
795 independent reflectionsθmax = 21.9°
Refinement top
R[F2 > 2σ(F2)] = 0.0590 restraints
wR(F2) = 0.183Only H-atom coordinates refined
S = 1.15Δρmax = 0.34 e Å3
795 reflectionsΔρmin = 0.34 e Å3
116 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
N10.3774 (9)0.0442 (3)0.7870 (2)0.0211 (10)
H10.404 (12)0.041 (5)0.765 (3)0.025*
N20.5651 (11)0.1590 (4)0.6746 (2)0.0256 (10)
H2A0.607 (13)0.081 (6)0.655 (3)0.031*
H2B0.649 (13)0.234 (5)0.652 (3)0.031*
C20.4541 (11)0.1664 (4)0.7498 (2)0.0201 (11)
N30.4177 (9)0.2891 (3)0.78463 (19)0.0225 (10)
C40.3014 (11)0.2830 (4)0.8611 (2)0.0201 (10)
C50.2209 (11)0.1636 (4)0.9017 (2)0.0205 (11)
O60.1943 (8)0.0830 (3)0.89372 (17)0.0258 (9)
C60.2561 (10)0.0331 (4)0.8648 (2)0.0203 (11)
N70.1204 (10)0.2027 (4)0.9772 (2)0.0240 (10)
H70.040 (13)0.148 (4)1.024 (3)0.029*
C80.1467 (12)0.3409 (4)0.9782 (3)0.0236 (11)
H80.108 (13)0.399 (5)1.025 (3)0.028*
N90.2563 (9)0.3949 (4)0.9098 (2)0.0234 (10)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N10.025 (2)0.0148 (19)0.0224 (19)0.0019 (14)0.0001 (15)0.0020 (15)
N20.032 (2)0.019 (2)0.026 (2)0.0011 (16)0.0023 (16)0.0007 (16)
C20.016 (2)0.021 (2)0.023 (2)0.0012 (16)0.0036 (16)0.0004 (17)
N30.0188 (19)0.024 (2)0.025 (2)0.0014 (14)0.0003 (14)0.0007 (15)
C40.013 (2)0.022 (2)0.024 (2)0.0005 (16)0.0030 (16)0.0004 (18)
C50.015 (2)0.021 (2)0.024 (2)0.0012 (16)0.0032 (17)0.0006 (17)
O60.0268 (18)0.0227 (17)0.0282 (17)0.0021 (12)0.0039 (12)0.0031 (13)
C60.009 (2)0.023 (2)0.028 (2)0.0017 (16)0.0002 (16)0.0036 (18)
N70.022 (2)0.025 (2)0.024 (2)0.0028 (15)0.0031 (14)0.0017 (15)
C80.018 (2)0.024 (2)0.028 (2)0.0017 (17)0.0022 (17)0.0002 (19)
N90.019 (2)0.026 (2)0.024 (2)0.0025 (14)0.0015 (15)0.0030 (15)
Geometric parameters (Å, º) top
N1—H10.91 (5)C4—N91.364 (5)
N1—C21.372 (5)C5—C61.412 (6)
N1—C61.387 (5)C5—N71.373 (5)
N2—H2A0.85 (5)O6—C61.249 (5)
N2—H2B0.88 (5)N7—H71.00 (5)
N2—C21.330 (6)N7—C81.342 (5)
C2—N31.330 (5)C8—H80.97 (5)
N3—C41.356 (5)C8—N91.328 (6)
C4—C51.378 (6)
H1—N1—C2125 (3)C4—C5—C6121.0 (4)
H1—N1—C6110 (3)C4—C5—N7106.7 (3)
C2—N1—C6124.6 (3)C6—C5—N7132.3 (4)
H2A—N2—H2B120 (5)N1—C6—C5111.8 (3)
H2A—N2—C2119 (3)N1—C6—O6120.0 (4)
H2B—N2—C2119 (3)C5—C6—O6128.3 (4)
N1—C2—N2117.0 (4)C5—N7—H7132 (2)
N1—C2—N3123.3 (4)C5—N7—C8105.2 (4)
N2—C2—N3119.7 (4)H7—N7—C8123 (2)
C2—N3—C4114.1 (3)N7—C8—H8125 (3)
N3—C4—C5125.2 (4)N7—C8—N9114.1 (4)
N3—C4—N9124.6 (4)H8—C8—N9121 (3)
C5—C4—N9110.2 (4)C4—N9—C8103.9 (3)
C6—N1—C2—N2179.5 (3)C2—N1—C6—O6179.8 (3)
C6—N1—C2—N30.4 (6)C4—C5—C6—N10.2 (5)
N1—C2—N3—C40.7 (5)C4—C5—C6—O6179.9 (4)
N2—C2—N3—C4179.7 (3)N7—C5—C6—N1178.3 (4)
C2—N3—C4—C50.6 (5)N7—C5—C6—O61.4 (7)
C2—N3—C4—N9177.7 (3)C4—C5—N7—C80.2 (4)
N3—C4—C5—C60.1 (6)C6—C5—N7—C8178.5 (4)
N3—C4—C5—N7179.0 (3)C5—N7—C8—N90.1 (5)
N9—C4—C5—C6178.4 (3)N7—C8—N9—C40.4 (5)
N9—C4—C5—N70.5 (4)N3—C4—N9—C8179.0 (4)
C2—N1—C6—C50.1 (5)C5—C4—N9—C80.5 (4)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···N3i0.91 (5)1.97 (5)2.862 (5)167 (4)
N2—H2A···N9i0.85 (5)2.17 (5)3.006 (5)173 (4)
N2—H2B···O6ii0.88 (5)2.03 (5)2.902 (5)174 (4)
N7—H7···O6iii1.00 (5)1.76 (5)2.742 (5)165 (4)
Symmetry codes: (i) x+1, y1/2, z+3/2; (ii) x+1, y+1/2, z+3/2; (iii) x, y, z+2.

Experimental details

Crystal data
Chemical formulaC5H5N5O
Mr151.14
Crystal system, space groupMonoclinic, P21/c
Temperature (K)120
a, b, c (Å)3.5530 (16), 9.693 (4), 16.345 (7)
β (°) 95.748 (6)
V3)560.1 (4)
Z4
Radiation typeSynchrotron, λ = 0.6712 Å
µ (mm1)0.14
Crystal size (mm)0.01 × 0.01 × 0.01
Data collection
DiffractometerBruker APEX2 CCD area-detector
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
3444, 795, 624
Rint0.054
θmax (°)21.9
(sin θ/λ)max1)0.556
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.059, 0.183, 1.15
No. of reflections795
No. of parameters116
H-atom treatmentOnly H-atom coordinates refined
Δρmax, Δρmin (e Å3)0.34, 0.34

Computer programs: APEX2 (Bruker, 2004), SAINT (Bruker, 2004), SAINT, SIR2002 (Burla et al., 2003), SHELXTL (Sheldrick, 2001), SHELXTL and DIAMOND (Brandenburg & Putz, 2004), SHELXTL and local programs.

Selected geometric parameters (Å, º) top
N1—C21.372 (5)C4—N91.364 (5)
N1—C61.387 (5)C5—C61.412 (6)
N2—C21.330 (6)C5—N71.373 (5)
C2—N31.330 (5)O6—C61.249 (5)
N3—C41.356 (5)N7—C81.342 (5)
C4—C51.378 (6)C8—N91.328 (6)
C2—N1—C6124.6 (3)C4—C5—N7106.7 (3)
N1—C2—N2117.0 (4)C6—C5—N7132.3 (4)
N1—C2—N3123.3 (4)N1—C6—C5111.8 (3)
N2—C2—N3119.7 (4)N1—C6—O6120.0 (4)
C2—N3—C4114.1 (3)C5—C6—O6128.3 (4)
N3—C4—C5125.2 (4)C5—N7—C8105.2 (4)
N3—C4—N9124.6 (4)N7—C8—N9114.1 (4)
C5—C4—N9110.2 (4)C4—N9—C8103.9 (3)
C4—C5—C6121.0 (4)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1···N3i0.91 (5)1.97 (5)2.862 (5)167 (4)
N2—H2A···N9i0.85 (5)2.17 (5)3.006 (5)173 (4)
N2—H2B···O6ii0.88 (5)2.03 (5)2.902 (5)174 (4)
N7—H7···O6iii1.00 (5)1.76 (5)2.742 (5)165 (4)
Symmetry codes: (i) x+1, y1/2, z+3/2; (ii) x+1, y+1/2, z+3/2; (iii) x, y, z+2.
 

Acknowledgements

The authors thank Dr R. W. Harrington and Mr Z. Yuan for assistance with data collection as part of the EPSRC National X-ray Crystallography Service at Station 9.8, SRS, Daresbury, England. We are grateful to the EPSRC for funding and to the CCLRC for synchrotron beam-time allocation.

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