Diethyl {[5-(2,4-dichlorophenyl)-1,3,4-thiadiazol-2-ylamino](4-methoxyphenyl)methyl}phosphonate

The title compound, C20H22Cl2N3O4PS, was synthesized by the reaction of N-(4-methoxybenzylidene)-5-(2,4-dichlorophenyl)-1,3,4-thiadiazol-2-amine and diethyl phosphite. In the crystal, intermolecular C—H⋯O and N—H⋯O hydrogen bonds link the molecules.

We report here the crystal structure of the title compound,(I). The molecular structure of (I) is shown in Fig.1. Bond lengths are in the normal ranges (Allen et al., 1987). The dihedral angle between the C15-C20 and S/C13/N2/N3/C14 is 32.4 (3)°, which shows that these two aromatic rings are not in the same plane. This dihedral angle is bigger than other phosphonate compounds, which is 7.54 (3)° (Wan et al., 2007) and 5.3 (2)° (Yin et al., 2008). There are intermolecular C -H···O and N-H···O hydrogen bonds (Fig. 2), which form chains along the b axis in the crystal.

S3. Refinement
All H atoms bonded to the C atoms were placed geometrically at the distances of 0.93-0.97 Å and included in the refinement in riding motion approximation with U iso (H) = 1.2 or 1.5U eq of the carrier atom.  A view of the molecular structure of (I). Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
Partial packing view showing the hydrogen-bonded network. Dashed lines indicate intermolecular C-H···O and N-H···O hydrogen bonds.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq