1:1 Hetero-assembly of 2-amino­pyrimidine and (+)-camphoric acid

In the title cocrystal, 2-aminopyrimidine–(+)-camphoric acid (1/1), C₄H₅N₃·C₁₀H₁₆O₄, the 2-amino­pyrimidine forms two eight-membered hydrogen-bonded rings with two different camphoric acid mol­ecules. This results in infinite wave-like chains of mol­ecules in which neighbouring chains are connected by weak C—H...O contacts. The five-membered ring in the acid mol­ecule adopts a half-chair conformation.

S1. Comment

Because of their strength as well as directional nature compared with other intermolecular non-covalent interactions (Lehn, 1995), hydrogen bonds are normally used as a tool in designing the structure of molecular crystals. Weak C—H···O contacts play a significant role in determining the molecular packing of organic solids (Taylor & Kennard, 1982). The crystal structure of 2-aminopyrimidine itself has been reported previously (Scheinbeim & Schempp, 1976; Furberg et al., 1979) and both the pyrimidine ring nitrogen and amine groups formed an eight-membered ring which leads to a hydrogen-bonded self-assembly. The pattern can be changed to a hetero-assembled structure where the donors (acid OH) are paired with the acceptors (ring N) (Etter et al., 1990). This communication reports the structure of the hydrogen-bonded heterodimer of 2-aminopyrimidine with camphoric acid, (I), where the 2-aminopyrimidine is hydrogen-bonded with the camphoric acid moiety to form typical eight-membered rings. \sch

The bond lengths and bond angles of the 2-aminopyrimidine and the camphoric acid molecules are comparable with the reported values (Etter et al., 1990; Furberg et al., 1979; Barnes et al., 1991). The five-membered ring of the acid molecule adopts a half-chair conformation, as observed in trans-π-camphanic acid (Hudson & Mills, 1972), with δC₂(C3) = 0.007 (2) Å (Nardelli, 1983). The twofold axis passes through C3 and intersects the C1—C5 bond. Atoms C1 and C5 deviate from the mean plane defined by the atoms C2, C3 and C4 by 0.316 (5) and -0.376 (5) Å, respectively.

In the crystal (Fig. 1), each acid molecule is linked to two 2-aminopyrimidine molecules and vice-versa by N—H···O and O—H···N intermolecular hydrogen bonds to form two symmetry-independent eight-membered rings each of which has the graph set motif of R²₂(8) (Bernstein et al., 1995). The eight-membered ring formed between the two moieties belonging to the same asymmetric unit (i.e. that ring involving N2 and O2) is almost planar with a maximum deviation from the plane of 0.111 (4) Å for O1. The second eight-membered ring, which contains O4 and N1ⁱ [symmetry code: (i) 3/2 - x, 1 - y, z - 1/2], is more twisted with the angle between the two four-atom planes defined by the acid and amine moieties being 23.8 (4)°. The maximum deviation from the mean ring plane is 0.321 (5) Å for O3. The mean plane through the five-membered ring in the acid molecule makes dihedral angles of 33.9 (2) and 38.3 (2)°, respectively, with the two adjacent pyrimidine rings described above. These hydrogen bonds thereby link the acid and amine moieties into infinite wave-like chains which extend parallel to the c axis (Fig. 2). The crystal structure is also characterized by alternate layers of camphoric acid and 2-aminopyrimidine molecules which lie parallel to the ab plane. This pattern has also been reported by De Santis et al. (1997). The neighbouring chains are interconnected by weak C—H···O interactions (Table 1) and are stacked along the b axis with C—H···π interactions involving the 2-aminopyrimidine molecules of 3.602 Å (C13—H13A = 0.93; H13A—Cg(-1/2 + x,3/2 - y,1 - z) = 2.893 Å; C13—H13A···Cg(-1/2 + x,3/2 - y,1 - z) = 134°; Cg = centroid of pyrimidine ring).

S2. Experimental

Single crystals of (I) were grown by evaporation of 1:1 mixture of 2-aminopyrimidine and (1R,3S)-(+)-camphoric acid in ethanol.

S3. Refinement

After checking their presence in the difference map, the positions of all H atoms were geometrically idealized and allowed to ride on their parent atoms.

Computing details

Data collection: SMART (Siemens, 1996); cell refinement: SAINT (Siemens, 1996); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PARST (Nardelli, 1995).

Figures

	Fig. 1. The structure of the title compound showing 30% probability displacement ellipsoids and the atom-numbering scheme.
	Fig. 2. The C—H···O interactions connecting neigbouring chains. The symmetry operators are shown in Table 1.

1:1 Hetero-assembly of 2-Aminopyrimidine and (+)-Camphoric acid

Crystal data

C4H5N3·C10H16O4	Dx = 1.220 Mg m^−3
Mr = 295.34	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, P212121	Cell parameters from 2297 reflections
a = 7.146 (1) Å	θ = 1.9–28.3°
b = 10.561 (1) Å	µ = 0.09 mm^−1
c = 21.306 (1) Å	T = 293 K
V = 1607.9 (3) Å^3	Needle, colourless
Z = 4	0.36 × 0.16 × 0.12 mm
F(000) = 632

Data collection

Siemens SMART CCD area detector diffractometer	1522 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.066
Graphite monochromator	θmax = 25.0°, θmin = 1.9°
Detector resolution: 8.33 pixels mm^-1	h = −7→8
ω scans	k = −12→12
8732 measured reflections	l = −23→25
2837 independent reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.065	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.159	See text
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0551P)^2 + 0.2628P] where P = (Fo^2 + 2Fc^2)/3
2837 reflections	(Δ/σ)max < 0.001
190 parameters	Δρmax = 0.15 e Å^−3
0 restraints	Δρmin = −0.15 e Å^−3

Special details

Experimental. The data collection covered over a hemisphere of reciprocal space by a combination of three sets of exposures; each set had a different ϕ angle (0, 88 and 180°) for the crystal and each exposure of 10 s covered 0.3° in ω. The crystal-to-detector distance was 4 cm and the detector swing angle was -35°. Crystal decay was monitored by repeating fifty initial frames at the end of data collection and analysing the intensity of duplicate reflections, and was found to be negligible.

The structure was solved by direct methods and refined by full-matrix least-squares techniques.

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.

Due to the large fraction of weak data at higher angles, the 2θ maximum was limited to 50°.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.6922 (5)	0.4267 (4)	0.45603 (17)	0.1010 (13)
O2	0.4145 (5)	0.4109 (3)	0.41117 (15)	0.0941 (12)
H2B	0.3886	0.4656	0.4370	0.141*
O3	0.7873 (5)	0.2860 (5)	0.16444 (15)	0.1243 (16)
O4	1.0585 (5)	0.2685 (3)	0.20989 (14)	0.0847 (11)
H4C	1.0945	0.2899	0.1749	0.127*
N1	0.2814 (5)	0.6715 (4)	0.59834 (14)	0.0609 (9)
N2	0.2747 (5)	0.5576 (3)	0.50153 (16)	0.0621 (10)
N3	0.5399 (5)	0.5687 (3)	0.56133 (15)	0.0650 (10)
H3C	0.5999	0.5937	0.5940	0.078*
H3D	0.5954	0.5231	0.5335	0.078*
C1	0.6683 (6)	0.3296 (4)	0.30229 (18)	0.0601 (11)
C2	0.7920 (7)	0.2255 (4)	0.27164 (18)	0.0677 (13)
H2A	0.7084	0.1544	0.2623	0.081*
C3	0.9274 (8)	0.1787 (5)	0.3227 (2)	0.1008 (19)
H3A	0.9292	0.0869	0.3241	0.121*
H3B	1.0533	0.2088	0.3146	0.121*
C4	0.8537 (7)	0.2329 (5)	0.3847 (2)	0.0888 (17)
H4A	0.8535	0.1684	0.4171	0.107*
H4B	0.9311	0.3030	0.3986	0.107*
C5	0.6545 (6)	0.2779 (4)	0.37133 (18)	0.0593 (11)
C6	0.5924 (7)	0.3788 (5)	0.4171 (2)	0.0685 (14)
C7	0.8780 (7)	0.2635 (5)	0.2105 (2)	0.0713 (13)
C8	0.7717 (8)	0.4569 (4)	0.3023 (2)	0.0917 (17)
H8A	0.7800	0.4884	0.2602	0.138*
H8B	0.8954	0.4455	0.3190	0.138*
H8C	0.7044	0.5165	0.3278	0.138*
C9	0.4834 (8)	0.3455 (6)	0.2690 (2)	0.0915 (16)
H9A	0.5047	0.3773	0.2274	0.137*
H9B	0.4068	0.4042	0.2919	0.137*
H9C	0.4210	0.2652	0.2666	0.137*
C10	0.5158 (8)	0.1670 (5)	0.3766 (2)	0.0981 (17)
H10A	0.5112	0.1381	0.4193	0.147*
H10B	0.5559	0.0990	0.3499	0.147*
H10C	0.3935	0.1948	0.3639	0.147*
C11	0.3612 (6)	0.6005 (4)	0.55374 (19)	0.0526 (11)
C12	0.1025 (7)	0.7027 (4)	0.5887 (2)	0.0663 (13)
H12A	0.0431	0.7538	0.6181	0.080*
C13	0.0023 (7)	0.6634 (4)	0.5376 (2)	0.0649 (12)
H13A	−0.1226	0.6854	0.5319	0.078*
C14	0.0966 (7)	0.5902 (4)	0.4955 (2)	0.0647 (12)
H14A	0.0320	0.5612	0.4605	0.078*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.069 (2)	0.139 (3)	0.096 (3)	0.010 (3)	−0.006 (2)	−0.050 (2)
O2	0.083 (3)	0.113 (3)	0.086 (2)	0.023 (2)	−0.013 (2)	−0.037 (2)
O3	0.076 (3)	0.231 (5)	0.065 (2)	−0.015 (3)	−0.008 (2)	0.046 (3)
O4	0.069 (2)	0.123 (3)	0.062 (2)	0.010 (2)	0.0024 (17)	0.0172 (19)
N1	0.057 (2)	0.071 (2)	0.054 (2)	0.002 (2)	0.0088 (19)	0.0007 (19)
N2	0.056 (3)	0.069 (2)	0.062 (2)	0.002 (2)	−0.008 (2)	−0.0017 (19)
N3	0.057 (2)	0.079 (3)	0.058 (2)	0.002 (2)	−0.0024 (19)	−0.0092 (19)
C1	0.061 (3)	0.058 (3)	0.062 (3)	0.004 (2)	0.003 (2)	0.007 (2)
C2	0.079 (3)	0.071 (3)	0.053 (3)	0.011 (3)	0.005 (2)	0.006 (2)
C3	0.116 (5)	0.122 (4)	0.065 (3)	0.050 (4)	0.015 (3)	0.027 (3)
C4	0.104 (4)	0.097 (4)	0.065 (3)	0.034 (3)	−0.002 (3)	0.011 (3)
C5	0.066 (3)	0.059 (3)	0.053 (3)	0.008 (2)	0.006 (2)	−0.001 (2)
C6	0.066 (4)	0.076 (3)	0.063 (3)	0.006 (3)	−0.004 (3)	0.000 (3)
C7	0.067 (4)	0.090 (4)	0.056 (3)	0.006 (3)	−0.001 (3)	0.007 (3)
C8	0.115 (5)	0.069 (3)	0.091 (4)	−0.011 (3)	0.017 (4)	0.013 (3)
C9	0.077 (4)	0.131 (5)	0.067 (3)	0.019 (4)	−0.003 (3)	0.003 (3)
C10	0.122 (5)	0.070 (3)	0.102 (4)	−0.019 (4)	0.020 (4)	0.000 (3)
C11	0.053 (3)	0.052 (3)	0.053 (3)	−0.001 (2)	0.006 (2)	0.011 (2)
C12	0.070 (4)	0.064 (3)	0.065 (3)	0.014 (3)	0.011 (3)	0.002 (2)
C13	0.058 (3)	0.067 (3)	0.070 (3)	0.003 (3)	−0.005 (3)	0.014 (3)
C14	0.066 (3)	0.065 (3)	0.063 (3)	−0.006 (3)	−0.004 (3)	0.002 (2)

Geometric parameters (Å, º)

O1—C6	1.204 (5)	C1—C2	1.554 (6)
O2—C6	1.322 (5)	C1—C5	1.572 (5)
O3—C7	1.200 (5)	C2—C7	1.495 (6)
O4—C7	1.291 (5)	C2—C3	1.538 (6)
N1—C12	1.336 (5)	C3—C4	1.533 (6)
N1—C11	1.338 (5)	C4—C5	1.527 (6)
N2—C14	1.325 (5)	C5—C6	1.511 (6)
N2—C11	1.351 (5)	C5—C10	1.538 (6)
N3—C11	1.330 (5)	C12—C13	1.367 (6)
C1—C9	1.509 (6)	C13—C14	1.362 (6)
C1—C8	1.534 (6)
C12—N1—C11	115.9 (4)	C6—C5—C1	112.2 (4)
C14—N2—C11	115.6 (4)	C4—C5—C1	103.0 (3)
C9—C1—C8	108.9 (4)	C10—C5—C1	111.9 (4)
C9—C1—C2	112.3 (4)	O1—C6—O2	121.8 (4)
C8—C1—C2	110.3 (4)	O1—C6—C5	124.5 (5)
C9—C1—C5	115.0 (4)	O2—C6—C5	113.6 (4)
C8—C1—C5	109.5 (4)	O3—C7—O4	121.5 (5)
C2—C1—C5	100.6 (3)	O3—C7—C2	122.9 (5)
C7—C2—C3	116.4 (4)	O4—C7—C2	115.5 (4)
C7—C2—C1	114.2 (4)	N3—C11—N1	117.7 (4)
C3—C2—C1	106.7 (4)	N3—C11—N2	117.1 (4)
C4—C3—C2	105.9 (4)	N1—C11—N2	125.3 (4)
C5—C4—C3	106.0 (4)	N1—C12—C13	123.3 (4)
C6—C5—C4	111.8 (4)	C14—C13—C12	115.9 (4)
C6—C5—C10	107.5 (4)	N2—C14—C13	124.0 (4)
C4—C5—C10	110.5 (4)
C9—C1—C2—C7	73.9 (5)	C2—C1—C5—C10	−76.7 (4)
C8—C1—C2—C7	−47.8 (5)	C4—C5—C6—O1	6.3 (7)
C5—C1—C2—C7	−163.3 (4)	C10—C5—C6—O1	127.7 (5)
C9—C1—C2—C3	−156.1 (4)	C1—C5—C6—O1	−108.9 (6)
C8—C1—C2—C3	82.3 (5)	C4—C5—C6—O2	−173.4 (4)
C5—C1—C2—C3	−33.3 (5)	C10—C5—C6—O2	−52.0 (5)
C7—C2—C3—C4	141.0 (5)	C1—C5—C6—O2	71.4 (5)
C1—C2—C3—C4	12.2 (6)	C3—C2—C7—O3	170.1 (5)
C2—C3—C4—C5	14.8 (6)	C1—C2—C7—O3	−64.8 (7)
C3—C4—C5—C6	−156.5 (4)	C3—C2—C7—O4	−8.6 (7)
C3—C4—C5—C10	83.9 (5)	C1—C2—C7—O4	116.5 (5)
C3—C4—C5—C1	−35.8 (5)	C12—N1—C11—N3	179.2 (4)
C9—C1—C5—C6	−76.7 (5)	C12—N1—C11—N2	−1.1 (6)
C8—C1—C5—C6	46.3 (5)	C14—N2—C11—N3	179.6 (4)
C2—C1—C5—C6	162.4 (4)	C14—N2—C11—N1	−0.1 (6)
C9—C1—C5—C4	162.8 (4)	C11—N1—C12—C13	1.6 (6)
C8—C1—C5—C4	−74.2 (5)	N1—C12—C13—C14	−0.8 (6)
C2—C1—C5—C4	42.0 (4)	C11—N2—C14—C13	1.0 (6)
C9—C1—C5—C10	44.2 (5)	C12—C13—C14—N2	−0.6 (7)
C8—C1—C5—C10	167.2 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2B···N2	0.82	1.87	2.665 (5)	163
O4—H4C···N1^i	0.82	1.90	2.713 (4)	170
N3—H3D···O1	0.86	2.06	2.910 (5)	170
N3—H3C···O3^ii	0.86	2.13	2.951 (5)	161
C12—H12A···O3^iii	0.93	2.59	3.221 (6)	125

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