Methyl 2-(4,6-dichloro-1,3,5-triazin-2-ylamino)acetate

The title compound, C6H6Cl2N4O2, was prepared by the nucleophilic substitution of 2,4,6-trichloro-1,3,5-triazine by glycine methyl ester hydrochloride, and was isolated from the reaction by using flash chromatography. The crystal structure at 150 K reveals the presence two crystallographically independent molecules in the asymmetric unit which differ in the orientation of the pendant methoxycarbonyl group. Each molecular unit is engaged in strong and highly directional N—H⋯N hydrogen-bonding interactions with a symmetry-related molecule, forming supramolecular dimers which act as the synthons in the crystal packing.

The title compound, C 6 H 6 Cl 2 N 4 O 2 , was prepared by the nucleophilic substitution of 2,4,6-trichloro-1,3,5-triazine by glycine methyl ester hydrochloride, and was isolated from the reaction by using flash chromatography. The crystal structure at 150 K reveals the presence two crystallographically independent molecules in the asymmetric unit which differ in the orientation of the pendant methoxycarbonyl group. Each molecular unit is engaged in strong and highly directional N-HÁ Á ÁN hydrogen-bonding interactions with a symmetry-related molecule, forming supramolecular dimers which act as the synthons in the crystal packing.
We are grateful to Fundaçã o para a Ciê ncia e a Tecnologia (FCT, Portugal) for their general financial support and also for specific funding toward the purchase of the single-crystal diffractometer. SV wishes to acknowledge the Associated Laboratory CICECO for a research grant.

Comment
Worldwide research on 1,3,5-triazine derivatives has increased quite considerably in recent years driven by the versatility of this molecule which allows the nucleophilic substitution of the chloride atoms by various functional groups such as carboxylic acids, amines, amides, chlorides, nitriles, among others (Blotny, 2006;Giacomelli et al., 2004). These reactions allow the engineering of novel derivative compounds which exhibit markedly different properties from their precursors. Hence, the isolated products can be ultimately employed in various areas such as in pharmaceutical sciences, in the textile industry, and in analytical chemistry. Following our interest in crystal engineering (Vilela et al., 2009;Shi et al., 2008;Paz & Klinowski, 2003Paz et al., 2002Paz et al., , 2005, we started using 2,4,6-trichloro-1,3,5-triazine as a molecular canvas for the preparation of novel multipodal organic ligands. A search in the literature and in the Cambridge Structural Database (CSD, Version of November 2008 with three updates; Allen, 2002) shows that the group of Bai  reported the only known examples of transition metal coordination polymers containing N,N',N''-1,3,5-triazine-2,4,6-triyltrisglycine. We intend to further develop their concept by preparing mono-, di-and tri-substitued derivatives with several amino acid pendant groups. By using glycine methyl ester hydrochloride (Vilela et al., 2009) we isolated the pure title compound (i.e., the monosubstituted derivative, I).
At 150 K compound (I) contains two identical molecular units in the asymmetric unit (Fig. 1). The bond lengths and angles observed for the two molecules are statistically identical. The pendant methoxycarbonyl group exhibits considerable conformational flexibility due to the possibility of rotation around the -CH 2 -moiety. Indeed, while the rings and the -NH-moiety of the two crystallographically independent molecular units are almost co-planar, the pendant group is rotated by ca 180° (Fig. 2), with this feature arising with the objective to minimize steric repulsion in the crystal structure (see below).
The co-planarity of the -NH-bond with the ring of each molecular unit seems to be promoted by the existence of two strong (d D···A being ca 3.02 Å) and highly directional [<(DHA) angles above 170° -see Table 1] N-H···N hydrogen bonding interactions that form a R 2 2 (8) graph set motif (Bernstein et al., 1995). This arrangement leads to the existence of supramolecular dimers (one for each molecular unit) in the crystal structure, with Fig. 3 depicting one of these. The close packing in the solid-state is based on the spatial interdigitation of the two dimers to effectively occupy the available space, hence the two conformations for the pendant groups which ultimately help promoting a more effective packing (Fig. 4).

Experimental
Glycine methyl ester hydrochloride (193 mg, 2.169 mmol; Sigma-Adrich, 99%) and potassium carbonate (200 mg, 1.447 mmol; Sigma-Aldrich, >99.0%) were added at 273 K to a solution of 2,4,6-trichloro-1,3,5-triazine (100 mg, 0.542 mmol; Sigma-Aldrich, >98,0%) in dried toluene (ca 5 ml). The reaction mixture was kept under magnetic stirring and slowly heated to reflux under an anhydrous atmosphere. The reaction was controlled by TLC and stopped after 24 h. The reaction mixture was separated by flash column chromatography using as eluent a gradient of methanol in dichloromethane. The first supplementary materials sup-2 isolated fraction was identified as (I) (7% yield). Single crystals were isolated from recrystallization of the crude product from a solution in dichloromethane: methanol (ca 1: 1). All employed solvents were of analytical grade and purchased from commercial sources.

Refinement
Hydrogen atoms bound to carbon were located at their idealized positions and were included in the model in the riding model approximation with C-H = 0.99 Å (for the -CH 2 -groups) or 0.98 Å (for the -CH 3 moieties). The isotropic thermal displacement parameters for these atoms were fixed at 1.2 (methylene) or 1.5 (methyl) times U eq of the carbon atom to which they are attached. The N-H atoms were located from difference Fourier maps and included in the structure with the N-H distance restrained to 0.95 (1) Å and with U iso fixed at 1.5 times U eq of the N atom.
The structure contains a large residual electron density of 1.78 e . Å -3 located at 1.36 Å of H4A. Attempts to include this peak as a disordered C atom did not lead to sensible structural refinements. Fig. 1. Molecular structures of the two independent molecules in (I). Non-hydrogen atoms are represented as thermal displacement ellipsoids drawn at the 50% probability level and hydrogen atoms as small spheres with arbitrary radii. The atomic labeling is provided for all nonhydrogen atoms. Fig. 2. Structure overlay of the two crystallographically independent molecular units comprising the asymmetric unit in (I): while the -NH group remains almost co-planar with the aromatic ring, the two methoxycarbonyl groups are mutually rotated by ca 180° around the -CH 2 -bond.    Methyl 2-(4,6-dichloro-1,3,5-triazin-2-ylamino)acetate 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 Rfactors(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.