2,2′-Dihydroxybiphenyl-3,3′-dicarbaldehyde dioxime

The molecule of the title compound, C14H12N2O4, lies across a crystallographic inversion centre situated at the mid-point of the C—C intra-annular bond. The molecule is not planar, the dihedral angle between the aromatic rings being 50.1 (1)°. The oxime group is in an E position with respect to the –OH group and forms an intramolecular O—H⋯N hydrogen bond. In the crystal structure, intermolecular O—H⋯O hydrogen bonds link molecules into chains propagating along [001]. The crystal structure is further stabilized by intermolecular stacking interactions between the rings [centroid-to-centroid distance = 3.93 (1) Å], resulting in layers parallel to the bc plane.

The molecule of the title compound, C 14 H 12 N 2 O 4 , lies across a crystallographic inversion centre situated at the mid-point of the C-C intra-annular bond. The molecule is not planar, the dihedral angle between the aromatic rings being 50.1 (1) . The oxime group is in an E position with respect to the -OH group and forms an intramolecular O-HÁ Á ÁN hydrogen bond. In the crystal structure, intermolecular O-HÁ Á ÁO hydrogen bonds link molecules into chains propagating along [001]. The crystal structure is further stabilized by intermolecular stacking interactions between the rings [centroid-to-centroid distance = 3.93 (1) Å ], resulting in layers parallel to the bc plane.

Comment
Oximes are a traditional class of chelating ligands widely used in coordination and analytical chemistry and extraction metallurgy (Kukushkin et al., 1996;Chaudhuri, 2003). Due to marked ability to from bridges between metal ions oxime ligands may be used for obtaining polynuclear compounds in the field of molecular magnetism and supramolecular chemistry (Cervera et al., 1997;Costes et al., 1998). Also, the oxime ligands are strong donors and therefore the oxime-containing ligands were found to efficiently stabilize high oxidation states of metal ions like Cu(III) and Ni(III) (Kanderal et al., 2005;Fritsky et al., 2006). The presence of additional donor groups together with the oxime group in the ligand molecule may result in significant increase of chelating efficiency and ability to form polynuclear complexes. The present investigation is dedicated to the study of the molecular structure of the title compound (I) which is a new polynuclear ligand containing both oxime and phenolic functions.
Molecules of I lie across a crystallographic inversion centre situated in the midpoint of the C-C intra-annular bond (Fig.   1). The molecule is not planar, the dihedral angle between the phenyl rings is 50.1 (1)°. The oxime group is in the E-position with respect to the OH group and forms an intramolecular O-H···N hydrogen bond. The C=N and N-O bond lengths are normal for oximes (Onindo et al., 1995;Sliva et al., 1997;Mokhir et al., 2002).
In the crystal structure, intermolecular O-H···O hydrogen bonds between the phenolic groups of the translational molecules link the molecules into chains propagating along [001]. The crystal structure is further stabilized by the intermolecular stacking interactions between the phenyl rings with centroid-to-centroid distances equal to 3.93 Å resulting in layers parallel to the yz plane (Fig. 2).

Refinement
The O-H hydrogen atoms were located from the difference Fourier map and refined isotropically. The C-H hydrogen atoms of the phenyl rings were positioned geometrically and were constrained to ride on their parent atoms, with C-H = 0.95 Å, and U iso = 1.2 U eq (parent atom).