Butylbis(dimethylglyoximato-κ2 N,N′)(pyridine-κN)cobalt(III)

In the title compound, [Co(C4H9)(C4H7N2O2)2(C5H5N)], which was prepared as a model complex of vitamin B12, the CoIII atom is coordinated by a butyl group, a pyridine and two N,N′-bidentate dimethylglyoximate ligands in a distorted octahedral geometry. The bis-chelating dimethylglyoximate ligands, which occupy equatorial sites, are linked by strong intramolecular O—H⋯O hydrogen bonds.


Comment
Organocobaloximes have extensively been used as structural and functional mimic for vitamin B 12 ever since these were first introduced by Schrauzer four decades ago as model of vitamin B 12 (Schrauzer & Kohnle, 1964;Schrauzer, 1968Schrauzer, , 1976).
These represent a unique class of compounds in organometallic and bioinorganic chemistry. These have rich coordination chemistry, application in organic synthesis and catalysis, and their stability and redox properties are of particular interest (Rockenbaur et al., 1982;Giese, 1986). The general formula of cobaloximes is RCo(L)B, where R is an organic group, bonded to cobalt, B is an axial base trans to the organic group, and L is a monoanionic dioxime ligand. Dimethylglyoximate (dmg) is a familiar ligand with excellent coordination capability to generate mono-, bi-or trinuclear complexes. Cobaloximes are best characterized by NMR and X-ray studies. Most of the recent studies on cobaloximes have been focused on their structure-property relationships (Gupta et al., 2004). We synthesized the title compound and determined its structure.
In the title compound, the cobalt atom is in a distorted octahedral geometry (Table 1)  The plane of the four nitrogen atoms is particular planar. The O-H···O bridge (Table 2) in the structure is very common in cobaloxime derivatives (Mandal & Gupta, 2005, 2007Kumar & Gupta, 2011). In packing diagram (Fig. 2), one unit cell contains two molecules.

Experimental
A solution of ClCo(dmgH) 2 py (1 mmol) in 10 ml of methanol was purged thoroughly with N 2 for 20 min and was cooled to 0 °C with stirring. The solution turned deep blue after the addition of a few drops of aqueous NaOH followed by sodium borohydride (1.5 mmol in 0.5 ml of water). The color of the solution turned orange-red on the addition of bromobutane (1.5 mmol). The reaction was stirred 1 h at 0 °C then poured into 20 ml chilled water. The resulting orange-red precipitate was filtered, washed with water, and dried. The crude product was purified on the silica gel column using dichloromethane.
The obtained orange colored compound was recrystallized from dichloromethane and methanol. After three days, orange colored crystals obtained which were suitable for single-crystal data collection.

Refinement
Atoms H1 and H2 were located in a difference Fourier map and were refined with the O-H distance restraints of 0.84 (2) Å.
Other hydrogen atoms were placed in calculated positions and included in the refinement in a riding-model approximation, with C-H = 0.95-0.99 Å, and with U iso (H) = 1.2U eq (C) or 1.5U eq (methyl C). Fig. 1. ORTEP diagram of the title compound with 50% probability displacement ellipsoids for non-hydrogen atoms.

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 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 Rfactors(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.