Diethyl N,N′-(p-phenylene)dioxamate

In the crystal structure, the molecule of the title compound, C14H16N2O6, is located on an inversion centre. The amide –NHCO– plane makes a dihedral angle of 34.08 (9)° with the benzene ring. The molecules are connected via intermolecular O—H⋯N hydrogen bonds into a two-dimensional network parallel to the bc plane. An intramolecular N—H⋯O hydrogen bond is also observed.

In the crystal structure, the molecule of the title compound, C 14 H 16 N 2 O 6 , is located on an inversion centre. The amide -NHCO-plane makes a dihedral angle of 34.08 (9) with the benzene ring. The molecules are connected via intermolecular O-HÁ Á ÁN hydrogen bonds into a two-dimensional network parallel to the bc plane. An intramolecular N-HÁ Á ÁO hydrogen bond is also observed.

Comment
Oxamido ligands were extensively investigated owing to their special biological properties and application prospects (Nonoyama et al., 1982). However, the ligands of oxalamic acid ethyl ester were rarely reported, in which ester group can stabilize the final compounds by producing complexes with main group and transition metals (Rios-Moreno et al., 2003).
In this work, the title compound, (I), was characterized by XRD single-crystal diffraction, element analysis and IR.
In the molecule (Fig. 1), the bond lengths containing O and N atoms are all consistent with corresponding values observed in similar systems (Navarro et al., 1998;Hashmi et al., 2004). There exists an intermolecular hydrogen bond involving the carboxamide O atom and the carboxamide N atom with a distance of 3.030 (3) Å, which are in agreement with those found in related compounds. Simultaneously, the molecule units are assembled into two dimensional structure with the intermolecular hydrogen-bond interactions.

Experimental
The synthesis method of the title compound is according to the previous literature method (Pardo et al., 2003). Colorless single crystals suitable for experiments were obtained from a methanol solution. Elemental analysis calculated for C 14 H 16 N 2 O 6 : C 54.54, H 5.23, N 9.09%; found C 54.52, H 5.22, N 9.08%. IR data: 3249 cm -1 (m, N-H), 1682 cm -1 (s, C=O).

Refinement
The H atom attached to the N atom was located in a different Fourier map and refined freely. Other hydrogen atoms were positioned geometrically with bond lengths C-H = 0.93-0.97 Å, and allowed to ride on their parent atoms, with U iso (H) = 1.2U eq (aromatic C) or 1.5U eq (methyl C). Fig. 1. The molecular structure of the title compound, with the unique atom-labelling scheme. The suffix A corresponds to symmetry code (-x + 2, -y, -z + 2). Displacement ellipsoids are drawn at the 30% probability level.  0.0558 (11) 0.0541 (12) 0.0400 (11) 0.0022 (9) 0.0000 (9) −0.0005 (9)