Pyrimidine-2,4-diamine acetone monosolvate

In the title compound, C4H6N4·C3H6O, the pyrimidine-2,4-diamine molecule is nearly planar (r.m.s. deviation = 0.005 Å), with the endocyclic angles covering the range 114.36 (10)–126.31 (10)°. In the crystal, N—H⋯N and N—H⋯O hydrogen bonds link the molecules into ribbons along [101], and weak C—H⋯π interactions consolidate further the crystal packing.


Timofeeva Comment
Pyrimidine derivatives are biologically important compounds, because they occur in nature as components of nucleic acids. Pyrimidine-2,4-diamine reacts with 3,4,5-trimethoxybenzyl to form trimethoprim which acts as the nucleic acid inhibitor (Hall et al., 1993) as well as with 3,7-dimethylxanthine to form clusters which represent potential alternate nucleobase pairs, geometrically equivalent to guanine-cytosine (Gengeliczki et al. 2011). In the area of drug design and pharmacore mapping, there are several compounds comprising the 2,4-diaminopyrimidinium cations and β-or ζdiketoenolate anions bound into supramolecular synthons by intermolecular hydrogen bonds (Bertolasi et al., 2002). The presented here crystal structure of the title compound, C 4 H 6 N 4 .C 3 H 6 O, (I) (Figure 1) was determined to study its hydrogen bonding system and to use it in the future for the design of co-crystals with particular properties.
The asymmetric unit of I consists of a pyrimidine-2,4-diamine molecule and an acetone solvate molecule. The pyrimidine-2,4-diamine molecule is planar (r.m.s. = 0.005 Å), with the endocyclic angles covering range of 114.36 (10)-126.31 (10)°. The endocyclic angles at the C2, C4 and C6 carbon atoms adjacent to the N1 and N3 heteroatoms are larger than 120°, and those at the other atoms of the ring are smaller than 120°. The analogous distribution of the endocyclic angles was recently observed by us within the related pyridine-2,5-diamine (Draguta et al., 2012). The bond lengths have the usual values (Allen et al., 1987).

Experimental
The compound I was obtained commercially (Aldrich) as a fine-crystalline powder. Crystals suitable for the X-ray diffraction study were grown by slow evaporation from acetone solution. The crystals of I are very sensitive to air and moisture. Therefore, to keep the quality of the crystal during the experiment, the crystal of I was mounted in vaseline oil.

Refinement
The hydrogen atoms of the amino groups were localized in the difference Fourier maps and refined isotropically. The 1.2U eq (C) for the CH-groups].

Computing details
Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.28 e Å −3 Δρ min = −0.28 e Å −3 Special details 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 F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.