6-[(Dimethylamino)methyleneamino]-1,3-dimethylpyrimidine-2,4(1H,3H)-dione dihydrate

Uracil, the pyrimidine nucleobase, which combined with adenine forms one of the major motifs present in the biopolymer RNA, is also involved in the self-assembly of RNA. In the title compound, C9H14N4O2·2H2O, the asymmetric unit contains one dimethylaminouracil group and two water molecules. The plane of the N=C—NMe2 side chain is inclined at 27.6 (5)° to the plane of the uracil ring. Both water molecules form O—H⋯O hydrogen bonds with the carbonyl O atoms of the uracil group. Additional water–water hydrogen-bond interactions are also observed in the crystal structure. The O—H⋯O hydrogen bonds lead to the formation of a two-dimensional hydrogen-bonded network cage consisting of two dimethylaminouracil groups and six water molecules.

Uracil, the pyrimidine nucleobase, which combined with adenine forms one of the major motifs present in the biopolymer RNA, is also involved in the self-assembly of RNA. In the title compound, C 9 H 14 N 4 O 2 Á2H 2 O, the asymmetric unit contains one dimethylaminouracil group and two water molecules. The plane of the N C-NMe 2 side chain is inclined at 27.6 (5) to the plane of the uracil ring. Both water molecules form O-HÁ Á ÁO hydrogen bonds with the carbonyl O atoms of the uracil group. Additional water-water hydrogen-bond interactions are also observed in the crystal structure. The O-HÁ Á ÁO hydrogen bonds lead to the formation of a two-dimensional hydrogen-bonded network cage consisting of two dimethylaminouracil groups and six water molecules.
AJT thanks the Department of Science and Technology (DST), Government of India, New Delhi, for financial support and SD thanks Tezpur University for an Institutional Fellowship.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: ER2056).

S1. Comment
Uracil, the pyrimidine nucleobase, combined with Adenine comprises one of the major motifs present in the biopolymer RNA, is also involved in the self-assembly of RNA (Sivakova & Rowan, 2005) The versatility of uracil and its derivatives, particularly the annulated one, is well recognized by synthetic (Sasaki et al., 1998) as well as biological chemists (Pontikis & Monneret, 1994) owing to their wide range of biological activities. The chemistry of uracil moiety and its derivatives have expanded enormously in the past decades only because of its mechanistic, synthetic and biological importance which made them of substantial experimental and theoretical interest.
Synthesis and characterization of the title compound (I) was reported recently from our laboratory (Thakur et al., 2001), through the reaction of 6-amino-1,3-dimethylbarbituric acid with (DMF-DMA) under thermal condition or Microwave irradiation in the solid state. Our ongoing present research program is aimed at synthesizing fused pyrimidine derivatives of biological significances. Also we have been investigating the rotational barrier of the two methyl groups in the exocyclic N9-Me 2 part in (I), which will help us in understanding the mechanism of the Diels Alder reaction of (I).
The asymmetric unit of (I), comprises one dimethylamino uracil moiety and two water molecules (Fig. 1). The sixmembered uracil ring is planar and the plane of its attached side chain is inclined 27.6 (5)° to the plane of the uracil ring.
The crystal structure is stabilized by O-H···O hydrogen bonds (Table 1). Both the water (O1W and O2W) molecules form O-H···O hydrogen bonds with the carbonyl (O1 and O2) atoms of the uracil moiety. In addition, water···water interactions are also observed in the crystal structure. The water molecules interconnect each other and in turn links the uracil moiety, thereby forming a two-dimensional hydrogen-bonded network cage consists of two dimethylamino uracil moieties and six water molecules (Fig.2).

S2. Experimental
In order to obtain suitable single crystals for this study, the title compound was dissolved in ethanol (98%) and the solution was allowed to evaporate very slowly.

S3. Refinement
The H atoms of the water molecules were located in a difference Fourier map and refined isotropically. Distance restraints were also applied to the H atoms of the water molecules with a set value of 0.86 (1) Å. All other H atoms were positioned geometrically and treated as riding on their parent C atoms, with C-H distances of 0.93 -0.96 Å, and with U iso (H) values of 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for the other H atoms. The methyl groups were allowed to rotate but not to tip.     where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.34 e Å −3 Δρ min = −0.21 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.063 (11)

Special details
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 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 > σ(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.