Tris(2,2′-bipyridine-κ2 N,N′)cobalt(III) bis[bis(pyridine-2,6-dicarboxylato-κ3 O 2,N,O 6)cobaltate(III)] perchlorate dimethylformamide hemisolvate 1.3-hydrate

In the title compound, [Co(C10H8N2)3][Co(C7H3NO4)2]2(ClO4)·0.5C3H7NO·1.3H2O, the CoIII atom in the complex cation is pseudooctahedrally coordinated by six N atoms of three chelating bipyridine ligands. The CoIII atom in the complex anion is coordinated by two pyridine N atoms and four carboxylate O atoms of two doubly deprotonated pyridine-2,6-dicarboxylate ligands in a distorted octahedral geometry. One dimethylformamide solvent molecule and two water molecules are half-occupied and one water molecule is 0.3-occupied. O—H⋯O hydrogen bonds link the water molecules, the perchlorate anions and the complex anions. π–π interactions between the pyridine rings of the complex anions are also observed [centroid–centroid distance = 3.804 (3) Å].

In the title compound, [Co(C 10 H 8 N 2 ) 3 ][Co(C 7 H 3 NO 4 ) 2 ] 2 -(ClO 4 )Á0.5C 3 H 7 NOÁ1.3H 2 O, the Co III atom in the complex cation is pseudooctahedrally coordinated by six N atoms of three chelating bipyridine ligands. The Co III atom in the complex anion is coordinated by two pyridine N atoms and four carboxylate O atoms of two doubly deprotonated pyridine-2,6-dicarboxylate ligands in a distorted octahedral geometry. One dimethylformamide solvent molecule and two water molecules are half-occupied and one water molecule is 0.3-occupied. O-HÁ Á ÁO hydrogen bonds link the water molecules, the perchlorate anions and the complex anions.

Iskenderov Comment
Polynuclear complexes and supramolecular assemblies containing both cationic and anionic modules are widely used in molecular magnetism, crystal engineering, bioinorganic modeling and catalysis (Fritsky et al., 2001(Fritsky et al., , 2004Krämer & Fritsky, 2000;Moroz et al., 2010;Thompson, 2002). Hydroxamic acids are extensively used in synthesis of discrete oligonuclear compounds (e.g. metallacrowns) (Golenya et al., 2012a,b;Mezei et al., 2007;Strotmeyer et al., 2004) and coordination polymers (Gumienna-Kontecka et al., 2007;Pavlishchuk et al., 2011). However, the synthesis of such compounds in aqueous solution under alkaline conditions is sometimes complicated by hydrolytic decomposition of the hydroxamate function resulting in the formation of carboxylic groups (Dobosz et al., 1998(Dobosz et al., , 1999Świątek-Kozłowska et al., 2000). Herein we report the crystal and molecular structure of the title compound obtained in the course of our attempt to obtain a mixed ligand binuclear cobalt complex as a result of hydrolytic decomposition of pyridine-2,6-dihydroxamic acid.
The title compound is ionic and contains discrete tris(2,2′-bipyridine)cobalt(III) cations, bis(pyridine-2,6-dicarboxylato)cobalt(III) complex anions, perchlorate anions and solvent DMF and water molecules (Fig. 1). The Co III atom in the complex cation is pseudooctahedrally coordinated by six N atoms of three chelating bipyridine ligands. The Co III atoms in the complex anions are coordinated by two pyridine N atoms and four carboxylate O atoms of two doubly deprotonated pyridine-2,6-dicarboxylate ligands in a distorted octahedral geometry. The values of Co-O and Co-N bond (Fritsky et al., 2003;Mokhir et al., 2002;Świątek-Kozłowska et al., 2000). This clearly indicates that the metal ions in both complex cation and anions are in trivalent state. The C-O bond lengths in the deprotonated carboxylate groups differ significantly [1.239 (2) and 1.292 (2) Å], which is typical for monodentately coordinated carboxylates (Wörl et al., 2005a, b). The C-N and C-C bond lengths in the 2,2′-bipyridine ligands and in the pyridine-2,6-dicarboxylate ligands are normal for 2-substituted pyridine derivatives (Moroz et al., 2008;Penkova et al., 2009;Sachse et al., 2008).
The crystal packing of the title compound is presented in Fig. 2. O-H···O hydrogen bonds link the water molecules, the perchlorate anions and the complex anions. π-π interactions between the pyridine rings of the complex anions are

Experimental
Cobalt(II) perchlorate hexahydrate (0.037 g, 0.1 mmol) was dissolved in methanol (5 ml) and mixed with a solution of pyridine-2,6-dihydroxamic acid (0.039 g, 0.2 mmol) synthesized according to Świątek-Kozłowska et al. (2002) in dimethylformamide (5 ml), then to the obtained mixture a solution of sodium hydroxide (0.1 M, 4 ml) was added. In a separate vessel, cobalt(II) perchlorate hexahydrate (0.037 g, 0.1 mmol) was dissolved in methanol (5 ml) and mixed with a solution of 2,2′-bipyridine (0.312 g, 2 mmol) in methanol (5 ml). Then the two obtained solutions were mixed, and the obtained mixture was stirred at 60 C° for 30 min and filtered. Dark red crystals suitable for X-ray analysis were obtained by slow diffusion of diethyl ether into the resulting solution at room temperature within 72 h. They were filtered off and washed with diethyl ether (yield: 62%).

Refinement
The DMF molecule was partially lost and therefore it was refined with occupancy of 0.5. The N13-C45 and N13-C46 distances in the DMF molecule were set to be equal. Also, C, N and O in DMF were refined with equal anisotropic displacement parameters. One of the water molecules was disordered over two sites with equal occupancies. Another water molecule was refined with occupancy factor of 0.3. The water H atoms were located from a difference Fourier map and constrained to ride on the parent atoms, with U iso (H) = 1.5U eq (O). Other H atoms were positioned geometrically and refined as riding atoms, with C-H = 0.95 (CH) and 0.98 (CH 3 ) Å and U iso (H) = 1.2(1.5 for methyl)U eq (C). The highest residual electron density was found at 1.06 Å from H46C atom and the deepest hole at 0.69 Å from Cl1 atom.   A packing diagram of the title compound. H atoms have been omitted for clarity.

Tris(2,2′-bipyridine-κ 2 N,N′)cobalt(III) bis[bis(pyridine-2,6-dicarboxylato-
where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 1.34 e Å −3 Δρ min = −1.11 e Å −3 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.