Bis{2-[(pyridin-2-yl)methylideneamino]benzoato-κ3 N,N′,O}chromium(III) nitrate monohydrate

The title complex salt hydrate, [Cr(C13H9N2O2)2]NO3·H2O, comprises discrete cations, nitrate anions and solvent water molecules. The CrIII atom is octahedrally coordinated by two anionic Schiff base ligands with the O atoms being cis. The two ligands differ significantly with dihedral angles between the pyridine and benzene rings of 4.8 (2) and 24.9 (2)°. The nitrate anion and solvent water molecule were modelled as being disordered, with the major components having site-occupancy values of 0.856 (14) and 0.727 (16), respectively. The crystal is built of alternating layers of cations and of anions plus water molecules, stacked along the c axis.

The title complex salt hydrate, [Cr(C 13 H 9 N 2 O 2 ) 2 ]NO 3 ÁH 2 O, comprises discrete cations, nitrate anions and solvent water molecules. The Cr III atom is octahedrally coordinated by two anionic Schiff base ligands with the O atoms being cis. The two ligands differ significantly with dihedral angles between the pyridine and benzene rings of 4.8 (2) and 24.9 (2) . The nitrate anion and solvent water molecule were modelled as being disordered, with the major components having site-occupancy values of 0.856 (14) and 0.727 (16), respectively. The crystal is built of alternating layers of cations and of anions plus water molecules, stacked along the c axis.

Structural commentary
The title compound was prepared during studies of the coordination behaviour of the tridentate carboxylate Schiff base ligand 2-N-(2′-pyridylimine)benzoic acid (HL) which results from the condensation between 2-pyridinecarbaldehide and anthranilic acid. Known metal complexes containing deprotonated HL (Dey et al., 2003;Mukhopadhyay et al., 2005;Sen et al., 2006) were prepared by in situ Schiff base synthesis -a synthetic approach utilized in the present work as well.
The title compound, Cr(C 13 H 10 N 2 O 2 ) 2 NO 3 . H 2 O, is formed of discrete [CrL 2 ] + cations, nitrate anions and solvent water molecules. The cation has no crystallographically imposed symmetry. The ligand molecules are deprotonated at the carboxylato oxygen atom and coordinate to the Cr III atom through the azomethine, pyridine-N and carboxylato-O atoms in such a way that the metal atom is octahedrally surrounded by two anionic ligands with cis O atoms ( Fig. 1 & Table 1). The two ligands differ significantly. The atoms of ligand 1 are virtually coplanar with the dihedral angle between the pyridyl and benzene rings being 4.8 (2)°. By contrast, in ligand 2 this dihedral angle is 24.9 (2)°.
The crystal lattice is built of alternating layers of cations and of anions plus water molecules (Fig. 2).

Synthesis and crystallization
The ligand HL was prepared by refluxing 2-pyridinecarbaldehyde (0.38 ml, 4 mmol) with anthranilic acid (0.55 g, 4 mmol) in methanol (20 ml) for 0.5 h. The resultant yellow solution was left in open air overnight and used without further purification.
To a stirred methanol solution (10 ml) of Cr(NO 3 ) 3 . 9H 2 O (0.80 g, 2 mmol) in a 50 ml conic flask, HL in methanol from the previous preparation was added. The solution was magnetically stirred at 323 K for 20 minutes. The brown precipitate was filtered off. The red-brown solution was left to evaporate at room temperature. Red-brown rod-like microcrystals of the title compound were formed in a few days. They were collected by filter-suction, washed with dry Pr i OH and finally dried in vacuo (yield: 45%).

Refinement
The nitrate anion and solvent water molecule were modelled as being disordered. The site occupancy factors of the major component of the nitrate refined to 0.856 (14), and that of the disordered water molecule to 0.727 (16). Minor components of the disordered atoms were refined with isotropic displacement parameters. Water molecule hydrogen atoms were not located. All remaining hydrogen atoms were added at calculated positions (C-H = 0.95 Å) and refined by use of a riding model, with U iso (H) = 1.2U eq (parent atom).

Figure 1
Molecular structure of the cation with the numbering scheme (the non-hydrogen atoms shown as 50% atomic displacement ellipsoids).

Crystal data
[Cr (C 13  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 0.43 e Å −3 Δρ min = −0.27 e Å −3 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 cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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. The nitrate anion and solvent water molecule were modelled as being disordered. The site occupancy factors of the two components of the nitrate refined to 0.856 (14) and its complement. Those for the two components of the disordered water molecule appeared to be significantly different and were refined to 0.727 (16) and its complement. Minor components of the disordered atoms were refined with isotropic displacement parameters. Water molecule hydrogen atoms were not located.

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