Two tautomeric polymorphs of 2,6-di­chloro­purine

García-Rubiño, M.E.; Choquesillo-Lazarte, D.; Núñez, M.C.; Campos, J.M.

doi:10.1107/S0108270111043575

organic compounds

STRUCTURAL
CHEMISTRY

ISSN: 2053-2296

Volume 67| Part 12| December 2011| Pages o484-o486

doi:10.1107/S0108270111043575

Two tautomeric polymorphs of 2,6-dichloropurine

M. Eugenia García-Rubiño,^a Duane Choquesillo-Lazarte,^b M. C. Núñez ^a and Joaquín M. Campos ^a ^*

^aDepartamento de Química Farmacéutica y Orgánica, Facultad de Farmacia, Universidad de Granada, Campus de Cartuja s/n, 18071 Granada, Spain, and ^bLaboratorio de Estudios Cristalográficos, IACT, CSIC-Universidad de Granada, Avenida de las Palmeras 4, 18100 Armilla, Granada, Spain
^*Correspondence e-mail: jmcampos@ugr.es

(Received 19 September 2011; accepted 20 October 2011; online 5 November 2011)

Two polymorphs of 2,6-dichloropurine, C₅H₂Cl₂N₄, have been crystallized and identified as the 9H- and 7H-tautomers. Despite differences in the space group and number of symmetry-independent molecules, they exhibit similar hydrogen-bonding motifs. Both crystal structures are stabilized by intermolecular N—H⋯N interactions that link adjacent molecules into linear chains, and by some nonbonding contacts of the C—Cl⋯π type and by π–π stacking interactions, giving rise to a crossed two-dimensional herringbone packing motif. The main structural difference between the two polymorphs is the different role of the molecules in the π–π stacking interactions.

Comment

2,6-Dichloropurine is an important pharmaceutical intermediate (Schaefer et al., 1978 ) used in the preparation of purine nucleosides and nucleotides, and other purine derivatives of great importance owing to their biological properties (Nair & Pal, 1998 ; Rao Kode & Phadtare, 2011 ).

Polymorphism, the ability of a given molecule to crystallize in different crystal structures, is a phenomenon often observed for organics (Bernstein, 2011 ; Brittain, 2011 ). The term `tautomeric polymorphs' refers to those tautomers of a given compound that crystallize in different crystal structures and they are very rarely observed (Cruz Cabeza et al., 2011 ). We present here the crystal structure of the 9H-, (I), and 7H-, (II), tautomers of 2,6-dichloropurine.

The molecular geometric parameters in the two presented polymorphs are similar, but the structures differ in the finer details of their crystal packing. As shown in Fig. 1, polymorph (I) crystallizes with two independent molecules in the asymmetric unit (A and B, top and middle) as the 9H-tautomer, while polymorph (II) crystallizes with one symmetry-independent molecule (bottom) as the 7H-tautomer.

The effect of the different –N(H) position in the tautomeric forms (N9 or N7) gives rise to subtle differences between the relevant bond lengths and angles in both structures in the imidazole ring. In (I), the N=Csp² bond corresponds to N7—C8 [1.310 (5) Å] and N17—C18 [1.307 (5) Å] for molecules A and B, respectively, while in (II) it is N9—C8 [1.327 (3) Å]. These N=Csp² bond lengths are comparable with those in related structures with 9H- (Mahapatra et al., 2008 ; Trávníček & Rosenker, 2006 ; Soriano-Garcia & Parthasarathy, 1977 ) and 7H-tautomers (Bo et al., 2006 ; Ikonen et al., 2009 ; Watson et al., 1965 ). The –N(H) tautomeric position is also evident from the greater ring angle at the site where the H atom is attached, namely N9 [C4—N9—C8 = 105.9 (3)°] and N19 [C14—N19—C18 = 105.6 (3)°] for (I), and N7 [C5—N7—C8 = 105.9 (2)°] for (II), compared with the ring angle involving the –N=C– bond [for (I), C5—N7—C8 = 103.6 (3)° and C15—N17—C18 = 103.8 (3)°; for (II), C4—N9—C8 = 103.6 (2)°]. In both polymorphs, the 2,6-dichloropurine molecules form linear chains along the b axis through intermolecular N—H⋯N interactions forming C(4) motifs (Bernstein et al., 1995 ).

In polymorph (I), chains built by molecules of type A are linked by intermolecular face-to-face π–π stacking interactions involving the N1/C2/N3/C4–C6 ring and a symmetry-related counterpart at (−x + 1, −y + 1, −z + 1), with a centroid–centroid distance of 3.493 (3) Å. Molecules of type B are not involved in π–π stacking interactions. There are also C—Cl⋯π interactions involving atom Cl16 and ring N1/C2/N3/C4–C6 (Cg1_I), with a Cl⋯centroid distance of 3.468 (2) Å and a C16—Cl16⋯Cg1_Iⁱ angle of 113.46 (17)° [symmetry code: (i) x, −y + $[{1\over 2}]$ , z + $[{1\over 2}]$ ], and atom Cl6 and ring N11/C12/N13/C14–C16 (Cg2_I), with a Cl⋯centroid distance of 3.664 (2) Å and a C6—Cl6⋯Cg2_I angle of 94.54 (13)°, resulting in a structure containing a two-dimensional herringbone-like motif of constituent molecules.

The crystal structure of polymorph (II) is similar to that of polymorph (I). Despite the fact that π–π stacking interactions are not observed in (II), the supramolecular structure features a similar herringbone motif to that in (I), due to the presence of C—Cl⋯π interactions between atom Cl6 and ring N1/C2/N3/C4–C6 (Cg1_II), with a Cl⋯centroid distance of 3.3471 (15) Å and a C6—Cl6⋯Cg1_IIⁱⁱ angle of 108.45 (10)° [symmetry code: (ii) x − $[{1\over 2}]$ , −y + $[{3\over 2}]$ , −z + 1]. As a consequence of the absence of stacking interactions in (II), the width of the herringbone motif (12.352 Å) is greater than that of (I) (11.797 Å) (Fig. 2) [the width of the motifs was calculated as the distance between the two planes containing the furthermost atoms in the herringbone motif, corresponding to the Cl atoms of 2,6-dichloropurine; Mercury (Macrae et al., 2008 )].

Figure 1
The contents of the asymmetric units of polymorph (I)

(top and middle) and polymorph (II)

(bottom), showing the atom-numbering schemes. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
A view of the crystal packing, showing the herringbone arrangement of 2,6-dichloropurine molecules in polymorph (I)

(left) and polymorph (II)

(right).

Experimental

Polymorph (I) (m.p. 466.05–466.75 K) was obtained unintentionally in an attempted synthesis of (RS)-2,6-dichloro-9-(2,3-dihydro-1,4-benzoxathiin-3-ylmethyl)-9H-purine (Díaz-Gavilán et al., 2008 ). Unreacted 2,6-dichloropurine was recovered using ethyl acetate as eluent. After concentrating the solvent under reduced pressure, suitable crystals of 2,6-dichloropurine were obtained after dissolving the compound in CH₂Cl₂. A vial with a screw top allowed slow evaporation of the solvent at room temperature to produce colourless crystals. Crystals of polymorph (II) (m.p. 467.95–468.85 K) were obtained by solvent evaporation with commercially available 2,6-dichloropurine using ethanol as solvent. The remarkable similarity of the crystal structures of the reported polymorphs yields minimal differences in the shape and position of the peaks in the FT–IR spectra (polycrystalline samples in KBr disks). Hence, the stretching mode ν(N—H) (a weak peak at 3210 cm⁻¹) and the in-plane deformation mode δ(N—H) (1513 cm⁻¹) appear at the same site in (I) and (II).

Polymorph (I)

Crystal data

C₅H₂Cl₂N₄
M_r = 189.01
Monoclinic, P 2₁ /c
a = 14.0867 (12) Å
b = 9.4898 (7) Å
c = 12.2656 (9) Å
β = 115.381 (4)°
V = 1481.4 (2) Å³
Z = 8
Cu Kα radiation
μ = 7.36 mm⁻¹
T = 296 K
0.12 × 0.10 × 0.06 mm

Data collection

Bruker X8 Proteum diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2001 ) T_min = 0.377, T_max = 0.753
18199 measured reflections
2547 independent reflections
1713 reflections with I > 2σ(I)
R_int = 0.085

Refinement

R[F² > 2σ(F²)] = 0.051
wR(F²) = 0.154
S = 1.10
2547 reflections
199 parameters
H-atom parameters constrained
Δρ_max = 0.27 e Å⁻³
Δρ_min = −0.29 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °) for polymorph (I)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N9—H9⋯N7ⁱ	0.86	1.96	2.785 (4)	161
N19—H19⋯N17ⁱⁱ	0.86	1.94	2.768 (5)	160
Symmetry codes: (i) $[-x+1, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (ii) $[-x+2, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]$ .

Polymorph (II)

Crystal data

C₅H₂Cl₂N₄
M_r = 189.01
Orthorhombic, P 2₁ 2₁ 2₁
a = 5.5716 (9) Å
b = 9.5820 (16) Å
c = 13.159 (2) Å
V = 702.5 (2) Å³
Z = 4
Mo Kα radiation
μ = 0.85 mm⁻¹
T = 120 K
0.12 × 0.10 × 0.08 mm

Data collection

Bruker SMART APEX diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2001) T_min = 0.905, T_max = 0.935
6847 measured reflections
1243 independent reflections
1156 reflections with I > 2σ(I)
R_int = 0.041

Refinement

R[F² > 2σ(F²)] = 0.033
wR(F²) = 0.071
S = 1.38
1243 reflections
100 parameters
H-atom parameters constrained
Δρ_max = 0.33 e Å⁻³
Δρ_min = −0.22 e Å⁻³
Absolute structure: Flack (1983 ), with 489 Friedel pairs
Flack parameter: 0.03 (10)

Table 2
Hydrogen-bond geometry (Å, °) for polymorph (II)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N7—H7⋯N9ⁱ	0.94	1.88	2.774 (3)	158
Symmetry code: (i) $[-x+1, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]$ .

H atoms on N atoms were located in difference maps and refined as riding, with N—H = 0.86 [in (I)] and 0.94 Å [in (II)], and U_iso(H) = 1.2U_eq(N). Other H atoms were positioned geometrically and treated as riding, with C—H = 0.93–0.95 Å and U_iso(H) = 1.2U_eq(C).

For both compounds, data collection: APEX2 (Bruker, 2010 ); cell refinement: SAINT (Bruker, 2010); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009 ); software used to prepare material for publication: publCIF (Westrip, 2010 ).

Supporting information

Crystal structure: contains datablocks I, II, global. DOI: 10.1107/S0108270111043575/gg3264sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S0108270111043575/gg3264Isup2.hkl

Structure factors: contains datablock II. DOI: 10.1107/S0108270111043575/gg3264IIsup3.hkl

Supporting information file. DOI: 10.1107/S0108270111043575/gg3264Isup4.cml

Comment top

2,6-Dichloropurine is an important pharmaceutical intermediate (Schaefer et al., 1978) used in the preparation of purine nucleosides and nucleotides, as well as other purine derivatives of great importance, owing to their biological properties (Nair & Pal, 1998; Rao Kode & Phadtare, 2011).

Polymorphism, the ability of a given molecule to crystallize in different crystal structures, is a phenomenon often observed for organics (Bernstein, 2011; Brittain, 2011). The term `tautomeric polymorphs' refers to those tautomers of a given compound that crystallize in different crystal structures and are very rarely observed (Cruz Cabeza et al., 2011). We present here the crystal structure of the 9H-, (I), and 7H-, (II), tautomers of 2,6-dichloropurine.

The molecular geometric parameters in the two presented polymorphs are similar, but the structures differ in the finer details of their crystal packing. As shown in Fig. 1, polymorph (I) crystallizes with two independent molecules in the asymmetric unit (A and B, top and middle) as the 9H- tautomer, while polymorph (II) crystallizes with one symmetry-independent molecule (bottom) as the 7H- tautomer.

The effect of the different –N(H) position in the tautomeric forms (N9 or N7) gives rise to subtle differences between the relevant bond lengths and angles in both structures in the imidazole ring. In (I), the N═Csp² bond corresponds to N7—C8 [1.310 (5) Å] and N17—C18 [1.307 (5) Å] for molecules A and B, respectively, while in (II) it involves N9—C8 [1.327 (3) Å]. These N═Csp² bond lengths are comparable with those in related structures with 9H- (Mahapatra et al., 2008; Trávníček & Rosenker, 2006; Soriano-Garcia & Parthasarathy, 1977) and 7H- tautomers (Bo et al., 2006; Ikonen et al., 2009; Watson et al., 1965). The –N(H) tautomeric position is also evident from the greater ring angle at the site where the H atom is attached, namely N9 [C4/N9/C8 105.9 (3)°] and N19 [C14/N19/C18 105.6 (3)°] for (I) and N7 [C5/N7/C8 105.9 (2)°] for (II), compared with the ring angle involving the –N═C– bond [for (I), C5—N7—C8 = 103.6 (3)° and C15—N17—C18 = 103.8 (3)°; for (II), C4—N9—C8 = 103.6 (2)°]. In both polymorphs, the 2,6-dichloropurine molecules form linear chains along the b axis through intermolecular N—H···N interactions with C(4) motifs (Bernstein et al., 1995).

In polymorph (I), chains built by molecules of type A are linked by intermolecular face-to-face π–π stacking interactions involving ring N1/C2/N3/C4–C6 and a symmetry-related ring (symmetry code: -x + 1, y + 1, -z + 1), with a centroid-to-centroid distance of 3.493 (3) Å. Molecules of type B are not involved in π–π stacking interactions. There are also C—Cl···π interactions involving atom Cl16 and ring N1/C2/N3/C4–C6 (Cg1_I), with a Cl···centroid distance of 3.468 (2) Å and a C16—Cl16···Cg1ⁱ_I angle of 113.46 (17)° [symmetry code: (i) x, -y + 1/2, z + 1/2], and atom Cl6 and ring N11/C12/N13/C14–C16 (Cg2_I), with a Cl···centroid distance of 3.664 (2) Å and a C6—Cl6···Cg2_I angle of 94.54 (13)°, resulting in a structure containing a two-dimensional herringbone-like motif of constituent molecules.

The crystal structure of polymorph (II) is similar to that of polymorph (I). Despite the fact that π–π stacking interactions are not observed in (II), the supramolecular structure features a similar herringbone motif to that in (I), due to the presence of C—Cl···π interactions between atom Cl6 and ring N1/C2/N3/C4–C6 (Cg1_II), with a Cl···centroid distance of 3.3471 (15) Å and a C6—Cl6···Cg1ⁱⁱ_II angle of 108.45 (10)° [symmetry code: (ii) x - 1/2, -y + 3/2, -z + 1]. As a consequence of the absence of stacking interactions in (II), the width of the herringbone motif (12.352 Å) is greater than that of (I) (11.797 Å) (Fig. 2).

Related literature top

For related literature, see: Bernstein (2011); Bernstein et al. (1995); Bo et al. (2006); Brittain (2011); Cruz & Groom (2011); Díaz-Gavilán, Conejo-García, Cruz-López, Núñez, Choquesillo-Lazarte, González-Pérez, Rodríguez-Serrano, Marchal, Aránega, Gallo, Espinosa & Campos (2008); Ikonen et al. (2009); Mahapatra et al. (2008); Nair & Pal (1998); Rao & Phadtare (2011); Schaefer et al. (1978); Soriano-Garcia & Parthasarathy (1977); Trávníček & Rosenker (2006); Watson et al. (1965).

Experimental top

Polymorph (I) (m.p. 466.05–466.75 K) was obtained unintentionally in an attempted synthesis of (RS)-2,6-dichloro-9-(2,3-dihydro-1,4-benzoxathiin-3-ylmethyl)-9H-purine (Díaz-Gavilán et al., 2008). Unreacted 2,6-dichloropurine was recovered using ethyl acetate as eluent. After concentrating the solvent under reduced pressure, suitable crystals of 2,6-dichloropurine were obtained after dissolving the compound in CH₂Cl₂. A vial with a screw top allowed the slow evaporation of the solvent at room temperature to produce colourless crystals. Crystals of polymorph (II) (m.p. 467.95–468.85 K) were obtained by solvent evaporation with commercially available 2,6-dichloropurine using ethanol as solvent. The remarkable similarity of the crystal structures of the reported polymorphs yields minimal differences in the shape and position of the peaks in the FT–IR spectra (polycrystalline samples in KBr disks). Hence, the stretching mode ν(N—H) (a weak peak at 3210 cm^-1) and the in-plane deformation mode δ(N—H) (1513 cm^-1) appear at the same site in (I) and (II).

Computing details top

For both compounds, data collection: APEX2 (Bruker, 2010); cell refinement: SAINT (Bruker, 2010); data reduction: SAINT (Bruker, 2010); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top

	Fig. 1. The asymmetric units of polymorph (I) (top and middle) and polymorph (II) (bottom), with the atom-numbering schemes. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. A view of the crystal packing, showing the herringbone arrangement of 2,6-dichloropurine molecules in polymorph (I) (left) and polymorph (II) (right).

(I) 2,6-dichloro-9H-purine top

Crystal data top

C₅H₂Cl₂N₄	F(000) = 752
M_r = 189.01	D_x = 1.695 Mg m⁻³
Monoclinic, P2₁/c	Cu Kα radiation, λ = 1.54178 Å
Hall symbol: -P 2ybc	Cell parameters from 2440 reflections
a = 14.0867 (12) Å	θ = 3.5–65.0°
b = 9.4898 (7) Å	µ = 7.36 mm⁻¹
c = 12.2656 (9) Å	T = 296 K
β = 115.381 (4)°	Cut block, colourless
V = 1481.4 (2) Å³	0.12 × 0.10 × 0.06 mm
Z = 8

Data collection top

Bruker X8 Proteum diffractometer	2547 independent reflections
Radiation source: fine-focus rotating anode	1713 reflections with I > 2σ(I)
Graded multilayer optics monochromator	R_int = 0.085
ϕ and ω scans	θ_max = 66.0°, θ_min = 5.8°
Absorption correction: multi-scan (SADABS; Bruker, 2001)	h = −16→16
T_min = 0.377, T_max = 0.753	k = −11→11
18199 measured reflections	l = −14→13

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.051	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.154	H-atom parameters constrained
S = 1.10	w = 1/[σ²(F_o²) + (0.0735P)² + 0.6074P] where P = (F_o² + 2F_c²)/3
2547 reflections	(Δ/σ)_max < 0.001
199 parameters	Δρ_max = 0.27 e Å⁻³
0 restraints	Δρ_min = −0.29 e Å⁻³

Crystal data top

C₅H₂Cl₂N₄	V = 1481.4 (2) Å³
M_r = 189.01	Z = 8
Monoclinic, P2₁/c	Cu Kα radiation
a = 14.0867 (12) Å	µ = 7.36 mm⁻¹
b = 9.4898 (7) Å	T = 296 K
c = 12.2656 (9) Å	0.12 × 0.10 × 0.06 mm
β = 115.381 (4)°

Data collection top

Bruker X8 Proteum diffractometer	2547 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2001)	1713 reflections with I > 2σ(I)
T_min = 0.377, T_max = 0.753	R_int = 0.085
18199 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.051	0 restraints
wR(F²) = 0.154	H-atom parameters constrained
S = 1.10	Δρ_max = 0.27 e Å⁻³
2547 reflections	Δρ_min = −0.29 e Å⁻³
199 parameters

Special details top

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. 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 > 2sigma(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

	x	y	z	U_iso*/U_eq
N1	0.6775 (3)	0.4986 (3)	0.6268 (3)	0.0531 (8)
C2	0.6641 (3)	0.6302 (5)	0.5827 (4)	0.0532 (10)
Cl2	0.71871 (10)	0.76088 (13)	0.68964 (11)	0.0745 (4)
N3	0.6148 (3)	0.6744 (3)	0.4701 (3)	0.0485 (8)
C4	0.5742 (3)	0.5666 (4)	0.3941 (3)	0.0449 (9)
C5	0.5820 (3)	0.4237 (4)	0.4254 (3)	0.0455 (9)
C6	0.6369 (3)	0.3951 (4)	0.5480 (3)	0.0501 (10)
Cl6	0.65201 (10)	0.22623 (12)	0.60104 (11)	0.0710 (4)
N7	0.5292 (3)	0.3429 (3)	0.3227 (3)	0.0506 (8)
C8	0.4929 (3)	0.4362 (4)	0.2358 (4)	0.0536 (10)
H8	0.4539	0.4114	0.1555	0.064*
N9	0.5165 (3)	0.5715 (3)	0.2720 (3)	0.0514 (8)
H9	0.4989	0.6455	0.2271	0.062*
N11	0.8212 (3)	0.2753 (4)	0.9484 (3)	0.0600 (9)
C12	0.8426 (3)	0.4071 (5)	0.9271 (4)	0.0569 (11)
Cl12	0.79181 (11)	0.53758 (13)	0.98390 (12)	0.0801 (4)
N13	0.8973 (3)	0.4514 (3)	0.8684 (3)	0.0560 (9)
C14	0.9317 (3)	0.3431 (4)	0.8255 (4)	0.0510 (10)
C15	0.9166 (3)	0.2009 (4)	0.8412 (4)	0.0521 (10)
C16	0.8593 (3)	0.1724 (4)	0.9055 (4)	0.0564 (10)
Cl16	0.83484 (10)	0.00077 (12)	0.93271 (12)	0.0798 (4)
N17	0.9637 (3)	0.1194 (4)	0.7842 (3)	0.0592 (9)
C18	1.0046 (4)	0.2121 (4)	0.7380 (4)	0.0618 (11)
H18	1.0419	0.1866	0.6941	0.074*
N19	0.9884 (3)	0.3483 (3)	0.7590 (3)	0.0590 (9)
H19	1.0095	0.4224	0.7353	0.071*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
N1	0.058 (2)	0.054 (2)	0.0489 (18)	−0.0015 (17)	0.0237 (16)	−0.0004 (17)
C2	0.054 (2)	0.058 (3)	0.056 (2)	−0.003 (2)	0.030 (2)	−0.006 (2)
Cl2	0.0826 (8)	0.0732 (8)	0.0662 (7)	−0.0190 (6)	0.0304 (6)	−0.0211 (6)
N3	0.060 (2)	0.0436 (18)	0.0478 (19)	−0.0046 (16)	0.0283 (16)	−0.0047 (15)
C4	0.055 (2)	0.040 (2)	0.046 (2)	−0.0004 (17)	0.0274 (19)	0.0028 (17)
C5	0.051 (2)	0.037 (2)	0.053 (2)	−0.0030 (17)	0.0269 (19)	−0.0018 (17)
C6	0.053 (2)	0.054 (2)	0.049 (2)	0.0043 (19)	0.0267 (19)	0.012 (2)
Cl6	0.0859 (8)	0.0571 (7)	0.0740 (7)	0.0127 (6)	0.0379 (7)	0.0202 (6)
N7	0.066 (2)	0.0346 (17)	0.0542 (19)	0.0030 (15)	0.0284 (17)	0.0011 (15)
C8	0.073 (3)	0.038 (2)	0.052 (2)	−0.0025 (19)	0.029 (2)	−0.0052 (18)
N9	0.072 (2)	0.0366 (17)	0.0465 (18)	0.0016 (15)	0.0267 (17)	0.0026 (14)
N11	0.068 (2)	0.054 (2)	0.065 (2)	−0.0005 (18)	0.035 (2)	−0.0045 (18)
C12	0.056 (3)	0.059 (3)	0.055 (2)	0.007 (2)	0.023 (2)	−0.007 (2)
Cl12	0.0956 (9)	0.0677 (8)	0.0907 (9)	0.0121 (7)	0.0528 (8)	−0.0122 (6)
N13	0.062 (2)	0.0447 (19)	0.063 (2)	0.0015 (16)	0.0287 (19)	−0.0038 (16)
C14	0.051 (2)	0.041 (2)	0.061 (2)	0.0010 (18)	0.024 (2)	−0.0018 (19)
C15	0.056 (2)	0.040 (2)	0.057 (2)	0.0015 (18)	0.021 (2)	−0.0019 (18)
C16	0.058 (3)	0.052 (2)	0.063 (3)	−0.001 (2)	0.030 (2)	0.004 (2)
Cl16	0.0988 (10)	0.0541 (7)	0.1062 (10)	−0.0107 (6)	0.0627 (8)	0.0022 (6)
N17	0.071 (2)	0.0411 (19)	0.077 (2)	0.0010 (17)	0.042 (2)	−0.0021 (17)
C18	0.070 (3)	0.046 (2)	0.077 (3)	0.001 (2)	0.039 (3)	−0.005 (2)
N19	0.069 (2)	0.0418 (18)	0.078 (2)	−0.0035 (17)	0.044 (2)	−0.0012 (17)

Geometric parameters (Å, º) top

N1—C6	1.324 (5)	N11—C16	1.327 (5)
N1—C2	1.341 (5)	N11—C12	1.339 (5)
C2—N3	1.320 (5)	C12—N13	1.328 (5)
C2—Cl2	1.728 (4)	C12—Cl12	1.720 (4)
N3—C4	1.336 (5)	N13—C14	1.337 (5)
C4—N9	1.365 (5)	C14—N19	1.367 (5)
C4—C5	1.401 (5)	C14—C15	1.392 (5)
C5—N7	1.387 (5)	C15—C16	1.376 (6)
C5—C6	1.392 (5)	C15—N17	1.387 (5)
C6—Cl6	1.708 (4)	C16—Cl16	1.726 (4)
N7—C8	1.310 (5)	N17—C18	1.307 (5)
C8—N9	1.352 (5)	C18—N19	1.356 (5)
C8—H8	0.9300	C18—H18	0.9300
N9—H9	0.8600	N19—H19	0.8600

C6—N1—C2	117.0 (3)	C16—N11—C12	116.5 (4)
N3—C2—N1	129.6 (4)	N13—C12—N11	129.3 (4)
N3—C2—Cl2	115.4 (3)	N13—C12—Cl12	115.5 (3)
N1—C2—Cl2	114.9 (3)	N11—C12—Cl12	115.2 (3)
C2—N3—C4	111.3 (3)	C12—N13—C14	111.2 (3)
N3—C4—N9	127.9 (3)	N13—C14—N19	127.6 (4)
N3—C4—C5	126.2 (3)	N13—C14—C15	126.1 (4)
N9—C4—C5	105.9 (3)	N19—C14—C15	106.3 (3)
N7—C5—C6	134.9 (4)	C16—C15—N17	134.8 (4)
N7—C5—C4	109.8 (3)	C16—C15—C14	115.6 (4)
C6—C5—C4	115.3 (3)	N17—C15—C14	109.7 (4)
N1—C6—C5	120.7 (4)	N11—C16—C15	121.3 (4)
N1—C6—Cl6	118.3 (3)	N11—C16—Cl16	118.0 (3)
C5—C6—Cl6	121.0 (3)	C15—C16—Cl16	120.7 (3)
C8—N7—C5	103.6 (3)	C18—N17—C15	103.8 (3)
N7—C8—N9	114.9 (4)	N17—C18—N19	114.7 (4)
N7—C8—H8	122.6	N17—C18—H18	122.7
N9—C8—H8	122.6	N19—C18—H18	122.7
C8—N9—C4	105.9 (3)	C18—N19—C14	105.6 (3)
C8—N9—H9	127.0	C18—N19—H19	127.2
C4—N9—H9	127.0	C14—N19—H19	127.2

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N9—H9···N7ⁱ	0.86	1.96	2.785 (4)	161
N19—H19···N17ⁱⁱ	0.86	1.94	2.768 (5)	160

Symmetry codes: (i) −x+1, y+1/2, −z+1/2; (ii) −x+2, y+1/2, −z+3/2.

(II) 2,6-dichloro-7H-purine top

Crystal data top

C₅H₂Cl₂N₄	F(000) = 376
M_r = 189.01	D_x = 1.787 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 4413 reflections
a = 5.5716 (9) Å	θ = 2.6–27.4°
b = 9.5820 (16) Å	µ = 0.85 mm⁻¹
c = 13.159 (2) Å	T = 120 K
V = 702.5 (2) Å³	Plate, colourless
Z = 4	0.12 × 0.10 × 0.08 mm

Data collection top

Bruker SMART APEX diffractometer	1156 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	R_int = 0.041
ϕ and ω scans	θ_max = 25.0°, θ_min = 2.6°
Absorption correction: multi-scan (SADABS; Bruker, 2001)	h = −6→6
T_min = 0.905, T_max = 0.935	k = −11→11
6847 measured reflections	l = −15→15
1243 independent reflections

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.033	H-atom parameters constrained
wR(F²) = 0.071	w = 1/[σ²(F_o²) + (0.0253P)²] where P = (F_o² + 2F_c²)/3
S = 1.38	(Δ/σ)_max = 0.006
1243 reflections	Δρ_max = 0.33 e Å⁻³
100 parameters	Δρ_min = −0.22 e Å⁻³
0 restraints	Absolute structure: Flack (1983), with how many Friedel pairs?
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.03 (10)

Crystal data top

C₅H₂Cl₂N₄	V = 702.5 (2) Å³
M_r = 189.01	Z = 4
Orthorhombic, P2₁2₁2₁	Mo Kα radiation
a = 5.5716 (9) Å	µ = 0.85 mm⁻¹
b = 9.5820 (16) Å	T = 120 K
c = 13.159 (2) Å	0.12 × 0.10 × 0.08 mm

Data collection top

Bruker SMART APEX diffractometer	1243 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2001)	1156 reflections with I > 2σ(I)
T_min = 0.905, T_max = 0.935	R_int = 0.041
6847 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.033	H-atom parameters constrained
wR(F²) = 0.071	Δρ_max = 0.33 e Å⁻³
S = 1.38	Δρ_min = −0.22 e Å⁻³
1243 reflections	Absolute structure: Flack (1983), with how many Friedel pairs?
100 parameters	Absolute structure parameter: 0.03 (10)
0 restraints

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
N1	−0.1017 (5)	0.6250 (3)	0.56651 (17)	0.0259 (6)
C2	−0.0199 (6)	0.4957 (3)	0.5851 (2)	0.0264 (7)
Cl2	−0.18790 (15)	0.36192 (8)	0.53068 (6)	0.0325 (2)
N3	0.1656 (5)	0.4541 (3)	0.63990 (19)	0.0262 (6)
C4	0.2858 (6)	0.5621 (3)	0.6803 (2)	0.0234 (7)
C5	0.2224 (6)	0.7022 (3)	0.6650 (2)	0.0237 (7)
C6	0.0226 (6)	0.7281 (3)	0.6077 (2)	0.0262 (7)
Cl6	−0.08278 (14)	0.89604 (7)	0.59069 (6)	0.0293 (2)
N7	0.3879 (4)	0.7792 (3)	0.71888 (17)	0.0254 (6)
H7	0.3936	0.8775	0.7233	0.030*
C8	0.5365 (6)	0.6864 (3)	0.7618 (2)	0.0251 (7)
H8	0.6678	0.7132	0.8035	0.030*
N9	0.4858 (5)	0.5539 (2)	0.7414 (2)	0.0262 (6)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
N1	0.0277 (14)	0.0230 (13)	0.0270 (13)	−0.0014 (12)	0.0019 (11)	0.0000 (10)
C2	0.0312 (18)	0.0212 (16)	0.0266 (16)	−0.0056 (14)	0.0030 (16)	−0.0006 (14)
Cl2	0.0378 (5)	0.0234 (4)	0.0363 (4)	−0.0044 (4)	−0.0058 (4)	−0.0034 (4)
N3	0.0295 (15)	0.0203 (14)	0.0289 (14)	−0.0013 (12)	0.0012 (13)	0.0002 (11)
C4	0.0266 (16)	0.0208 (17)	0.0229 (15)	−0.0018 (14)	0.0037 (14)	0.0010 (13)
C5	0.0285 (18)	0.0213 (17)	0.0213 (14)	−0.0035 (14)	0.0042 (14)	−0.0008 (13)
C6	0.0321 (18)	0.0203 (16)	0.0261 (17)	0.0026 (14)	0.0078 (15)	0.0041 (14)
Cl6	0.0328 (4)	0.0217 (4)	0.0335 (4)	0.0030 (3)	−0.0002 (4)	0.0008 (3)
N7	0.0302 (15)	0.0183 (13)	0.0277 (13)	−0.0011 (12)	0.0014 (13)	0.0017 (11)
C8	0.0266 (19)	0.0273 (17)	0.0215 (15)	−0.0025 (14)	0.0004 (14)	0.0003 (14)
N9	0.0337 (16)	0.0170 (13)	0.0278 (14)	0.0002 (12)	−0.0018 (13)	0.0004 (12)

Geometric parameters (Å, º) top

N1—C6	1.323 (4)	C5—C6	1.367 (4)
N1—C2	1.342 (4)	C5—N7	1.378 (4)
C2—N3	1.322 (4)	C6—Cl6	1.728 (3)
C2—Cl2	1.741 (3)	N7—C8	1.340 (4)
N3—C4	1.343 (4)	N7—H7	0.9442
C4—N9	1.376 (4)	C8—N9	1.327 (3)
C4—C5	1.403 (4)	C8—H8	0.9500

C6—N1—C2	115.9 (3)	N1—C6—C5	121.1 (3)
N3—C2—N1	130.0 (3)	N1—C6—Cl6	117.7 (2)
N3—C2—Cl2	115.0 (2)	C5—C6—Cl6	121.1 (2)
N1—C2—Cl2	115.0 (2)	C8—N7—C5	105.9 (2)
C2—N3—C4	112.0 (3)	C8—N7—H7	128.0
N3—C4—N9	126.3 (3)	C5—N7—H7	126.0
N3—C4—C5	123.7 (3)	N9—C8—N7	114.7 (3)
N9—C4—C5	110.0 (3)	N9—C8—H8	122.6
C6—C5—N7	137.0 (3)	N7—C8—H8	122.6
C6—C5—C4	117.2 (3)	C8—N9—C4	103.6 (2)
N7—C5—C4	105.7 (3)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N7—H7···N9ⁱ	0.94	1.88	2.774 (3)	158

Symmetry code: (i) −x+1, y+1/2, −z+3/2.

Experimental details

	(I)	(II)
Crystal data
Chemical formula	C₅H₂Cl₂N₄	C₅H₂Cl₂N₄
M_r	189.01	189.01
Crystal system, space group	Monoclinic, P2₁/c	Orthorhombic, P2₁2₁2₁
Temperature (K)	296	120
a, b, c (Å)	14.0867 (12), 9.4898 (7), 12.2656 (9)	5.5716 (9), 9.5820 (16), 13.159 (2)
α, β, γ (°)	90, 115.381 (4), 90	90, 90, 90
V (Å³)	1481.4 (2)	702.5 (2)
Z	8	4
Radiation type	Cu Kα	Mo Kα
µ (mm⁻¹)	7.36	0.85
Crystal size (mm)	0.12 × 0.10 × 0.06	0.12 × 0.10 × 0.08

Data collection
Diffractometer	Bruker X8 Proteum diffractometer	Bruker SMART APEX diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2001)	Multi-scan (SADABS; Bruker, 2001)
T_min, T_max	0.377, 0.753	0.905, 0.935
No. of measured, independent and observed [I > 2σ(I)] reflections	18199, 2547, 1713	6847, 1243, 1156
R_int	0.085	0.041
(sin θ/λ)_max (Å⁻¹)	0.593	0.594

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.051, 0.154, 1.10	0.033, 0.071, 1.38
No. of reflections	2547	1243
No. of parameters	199	100
H-atom treatment	H-atom parameters constrained	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.27, −0.29	0.33, −0.22
Absolute structure	?	Flack (1983), with how many Friedel pairs?
Absolute structure parameter	?	0.03 (10)

Computer programs: APEX2 (Bruker, 2010), SAINT (Bruker, 2010), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009), publCIF (Westrip, 2010).

Hydrogen-bond geometry (Å, º) for (I) top

D—H···A	D—H	H···A	D···A	D—H···A
N9—H9···N7ⁱ	0.86	1.96	2.785 (4)	160.9
N19—H19···N17ⁱⁱ	0.86	1.94	2.768 (5)	160.4

Symmetry codes: (i) −x+1, y+1/2, −z+1/2; (ii) −x+2, y+1/2, −z+3/2.

Hydrogen-bond geometry (Å, º) for (II) top

D—H···A	D—H	H···A	D···A	D—H···A
N7—H7···N9ⁱ	0.94	1.88	2.774 (3)	157.7

Symmetry code: (i) −x+1, y+1/2, −z+3/2.

Acknowledgements

The project `Factoría de Cristalización, CONSOLIDER INGENIO-2010' provided X-ray structural facilities for this work.

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ISSN: 2053-2296

Volume 67| Part 12| December 2011| Pages o484-o486

doi:10.1107/S0108270111043575