Benzyl N-(1-{N′-[(E)-2,3-dihydroxybenzylidene]hydrazinecarbonyl}-2-hydroxyethyl)carbamate dihydrate

The organic molecule in the title dihydrate, C18H19N3O6·2H2O, adopts a twisted U-shape with the major twists evident about the chiral C atom [the C—N—C—C torsion angle is −88.2 (4) °] and about the oxygen–benzyl bond [C—O—C—C = 74.2 (4) °]. The conformation about the imine bond [1.290 (4) Å] is E and an intramolecular O—H⋯N hydrogen bond helps to establish the near coplanarity of the hydroxybenzene and hydrazine groups. The crystal packing features O—H⋯O and N—H⋯O hydrogen bonds, leading to two-dimensional supramolecular arrays in the ab plane with weak C—H⋯π connections between the arrays.

The crystallographic asymmetric unit of (I) comprises an organic molecule and two water molecules of crystallization.
While the absolute structure could not be determined experimentally, the assignment of the S-configuration at the C9 atom is based on a starting reagent, L-serine. Overall, the organic molecule has a twisted U-shape with the two benzene rings lying to the same side of the molecule. Twists are evident about the chiral centre [the C11-N3-C9-C8 torsion angle is -88.2 (4) °] and about the benzyl group [C11-O6-C12-C13 is 74.2 (4) °]. The co-planarity at the hydroxylbenzene/hydrazine residue arises as a result of an intramolecular O1-H···N1 hydrogen bond (Table 1). The conformation about the N1═C7 imine bond [1.290 (4) Å] is E.
In the crystal, each of the acidic hydrogen atoms forms a significant hydrogen bond (Table 1). Thus, the O2-and O4hydroxy groups form hydrogen bonds to the water-O1w and hydroxy-O1 atoms, respectively. The O1w-water molecule forms hydrogen bonds to the hydroxy-O2 and water-O2w atoms, while the O2w-water molecule forms connections to symmetry related carbonyl-O3 atoms, implying the latter is bifurcated. Finally, amine-N2-H is connected to carbonyl-O5, and amine-N3-H is connected to water-O2w. The result of the hydrogen bonding scheme is the formation of layers in the ab plane, Fig. 2. Connections between layers that stack along the c axis are of the form C-H···π, Table 1.
The O-and N-bound H atoms were located from a difference map and refined with the distance restraints O-H = 0.84 ± 0.01 and N-H = 0.86±0.01 Å, and with U iso (H) = zU eq (carrier atom); z = 1.5 for O and z = 1.2 for N. In the absence of significant anomalous scattering effects, 1782 Friedel pairs were averaged in the final refinement. However, the absolute configuration was assigned on the basis of the chirality of the L-serine starting material. Fig. 1. The molecular structure of (I) showing displacement ellipsoids at the 50% probability level.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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 > 2σ(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.