Diaquabis(pyridine-2-carboxylato-κ2 N,O)manganese(II) dimethylformamide hemisolvate

There are two crystallographically independent complex molecules with very similar geometries in the unit cell of the title compound, [Mn(C6H4NO2)2(H2O)2]·0.5C3H7NO. The central ion is situated in a distorted octahedral environment of two N- and four O-donor atoms from two pyridine-2-carboxylate ligands and two cis-disposed water molecules. The carboxylate ligands are coordinated in a chelate fashion with the formation of two five-membered rings. In the crystal, the complex molecules are connected by O—H⋯O hydrogen bonds between the coordinated water molecules and the uncoordinated carboxylate O atoms, thus forming hydrogen-bonded walls disposed perpendicularly to the bc plane.

There are two crystallographically independent complex molecules with very similar geometries in the unit cell of the title compound, [Mn(C 6 H 4 NO 2 ) 2 (H 2 O) 2 ]Á0.5C 3 H 7 NO. The central ion is situated in a distorted octahedral environment of two N-and four O-donor atoms from two pyridine-2carboxylate ligands and two cis-disposed water molecules. The carboxylate ligands are coordinated in a chelate fashion with the formation of two five-membered rings. In the crystal, the complex molecules are connected by O-HÁ Á ÁO hydrogen bonds between the coordinated water molecules and the uncoordinated carboxylate O atoms, thus forming hydrogenbonded walls disposed perpendicularly to the bc plane.

Comment
Polynuclear complexes based on hydroxamic and carboxylate ligands are widely used in coordination chemistry and molecular magnetism (Sliva et al., 1997;Fritsky et al., 1998;Mokhir et al., 2002;Sachse et al., 2008). In the course of synthesis of polynuclear compounds, the hydroxamic functions (especially those neighboring with adjacent alternative donor groups) sometimes undergo hydrolytic destruction (Dobosz et al., 1999;Świątek-Kozłowska et al., 2000). The title compound was obtained as a result of hydrolytic decomposition of pyridine-2-hydroxamic acid by reaction with manganese(III) acetate.
The central ion of the title compound is situated in a distorted octahedral environment of two N and four O donor atoms from two pyridine-2-carboxylates and two cis-disposed water molecules (Fig. 1). The carboxylate ligands are coordinated in a chelate fashion with formation of two five-membered rings.
In the crystal neighboring complex molecules are connected through H-bonds between the coordinated water molecules and the non-coordinated carboxylic O atoms thus forming H-bonded walls disposed perpendicularly to the yz plane (Fig.2).

Refinement
Water O-H hydrogen atoms were located from a difference Fourier map. In the final refinement cycles they were constrained to ride on the parent atoms with U iso = 1.5 U eq (parent atom). The remaining H atoms were positioned geometrically and were constrained to ride on their parent atoms with C-H = 0.95-0.987 Å, and with U iso = 1.2-1.5 U eq (parent atom).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.