Trimethyl 2,2′,2′′-[1,3,5-triazine-2,4,6-triyltris(azanediyl)]triacetate

The title compound, C12H18N6O6, was synthesized via nucleophilic substitution by reacting 2,4,6-trichloro-1,3,5-triazine with glycine methyl ester hydrochloride in reflux (dried toluene) under anhydrous atmosphere. Individual molecules self-assemble via strong N—H⋯O hydrogen bonds into supramolecular double tapes running parallel to the [010] crystallographic direction. The close packing of supramolecular tapes is mediated by geometrical reasons in tandem with a number of weaker N—H⋯O and C—H⋯N hydrogen-bonding interactions.

The title compound, C 12 H 18 N 6 O 6 , was synthesized via nucleophilic substitution by reacting 2,4,6-trichloro-1,3,5triazine with glycine methyl ester hydrochloride in reflux (dried toluene) under anhydrous atmosphere. Individual molecules self-assemble via strong N-HÁ Á ÁO hydrogen bonds into supramolecular double tapes running parallel to the [010] crystallographic direction. The close packing of supramolecular tapes is mediated by geometrical reasons in tandem with a number of weaker N-HÁ Á ÁO and C-HÁ Á ÁN hydrogenbonding interactions.

Related literature
For background to nucleophilic reactions of 1,3,5-triazine, see: Blotny (2006); Giacomelli et al. (2004). For coordination polymers based on N,N 0 ,N 00 -1,3,5-triazine-2,4,6-triyltrisglycine, see: Wang et al. (2007a,b,c). For previous work from our research group on the synthesis of derivatives of 2,4,6trichloro-1,3,5-triazine from reactions with glycine methyl ester hydrochloride, see: Vilela et al. (2009a,b Table 1 Hydrogen-bond geometry (Å , ). Comment 2,4,6-Trichloro-1,3,5-triazine is a versatile organic molecule which can be used for the design and construction of larger entities because the three chlorine atoms are prone to nucleophilic substitution by several functional groups to form amides, nitriles and carboxylic acids, among several others (Blotny, 2006;Giacomelli et al., 2004). Resulting compounds exhibit specific physico-chemical properties which render them of potential academic and industrial interest (e. g., in the textile and pharmaceutical industries). Following our interest on crystal engineering of functional solids we have been using 2,4,6-trichloro-1,3,5-triazine as a molecular canvas for the design and synthesis of novel multipodal organic ligands. For instance, we have recently reported the synthesis and structural characterization of the monosubstituted form of the title compound: methyl 2-(4,6-dichloro-1,3,5-triazin-2-ylamino)acetate (Vilela et al., 2009a). Following the same reaction procedure we were able to isolate the title compound (the trisubstituted derivative) as a pure phase. Noteworthy, the title molecule can be a precursor of N,N',N''-1,3,5-triazine-2,4,6-triyltrisglycine which has been used in the construction of a number of transition metal coordination polymers (Wang et al., 2007a,b,c).
The complete nucleophilic substitution of the chlorine atoms of the chlorotriazine ring by methyl glycinate (Vilela et al., 2009b) led to the isolation in the solid state of the title compound (see Scheme). This novel compound crystallizes in the monoclinic centrosymmetric C2/c space group with one whole molecular unit composing the asymmetric unit as represented in Figure 1. The presence of three pendant substituent groups imposes significant steric impediment around the aromatic ring, ultimately preventing the existence of onset π-π stacking interactions as reported in the crystal packing of the monosubstituted analogue compound (Vilela et al., 2009a). In addition, the spatial arrangement of the pendant groups promotes a minimization of the overall steric repulsion: adjacent pendant moieties are either pointing toward different sides of the ring or, when located on the same side, the N-C bond rotates so the groups are as far away as possible from each other ( Figure 1).
The N-H groups are hydrogen-bonded to two carbonyl groups from adjacent molecular units. O4 acts as a double acceptor of two strong (d D···A in the 2.91-2.99 Å range) and highly directional [<(DHA) angle in the 168-172° range] N-H···O hydrogen bonding interactions ( Figure 2 and Table 1). These interactions lead to the formation of a double tape of molecular units running along the [010] crystallographic direction. As represented in Figure 3, the pendant groups point outwards of the double tape, thus allowing for an effective close packing of tapes in the crystal structure. Besides these pure geometrical reasons, the N6-H6 moieties located in the periphery establish physical connections between adjacent supramolecular tapes via a weaker N-H···O hydrogen bond (not shown; see Table 1 for geometrical details). It is also worth to mention that the presence of several crystallographically independent -CH 2 -and terminal -CH 3 groups in close  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 anhydrous atmosphere. The progress of the reaction was monitored by TLC and stopped after 24 h. The reaction mixture was then separated by flash column chromatography using as eluent a gradient (from 0 to 5%) of methanol in dichloromethane. The third isolated fraction was identified as the title compound (27% yield). Single crystals suitable for X-ray analysis were isolated from recrystallization of the crude product from a solution of 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 final structural model in riding-motion approximation with C-H distances of 0.99 Å (-CH 2 -groups) or 0.98 Å (terminal -CH 3 groups). The isotropic thermal displacement parameters for these atoms were fixed at 1.2 (-CH 2 -) or 1.5 (-CH 3 moieties) times U eq of the carbon atom to which they are attached.
All hydrogen atoms associated with the NH moieties were directly located from difference Fourier maps and included in the structure with the N-H distances restrained to 0.95 (1) Å and with U iso fixed at 1.5 times U eq of the N atom to which they are attached. Fig. 1. Schematic representation of the molecular unit of the title compound. Non-hydrogen atoms are represented as thermal ellipsoids drawn at the 50% probability level and hydrogen atoms as small spheres with arbitrary radii. The atomic labeling scheme is provided for all non-hydrogen atoms. Fig. 2. Fragment of the crystal structure emphasizing the contacts interconnecting adjacent chemical entities. The C=O4 carbonyl groups act as double acceptors in strong and highly directional N-H···O hydrogen bonds promoting the formation of a supramolecular double tape. For geometric details on the represented hydrogen bonds see Table 1. Symmetry transformations used to generate equivalent atoms have been omitted for clarity.   Table 1.

Figures
Trimethyl 2,2',2''-[1,3,5-triazine-2,4,6-triyltris(azanediyl)]triacetate 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.