Chloro(pyridine)cobaloxime is a coordination compound containing a CoIII center with octahedral coordination. It has been considered as a model compound of vitamin B12 for studying the properties and mechanism of action of the vitamin. It belongs to a class of bis(dimethylglyoximato)cobalt(III) complexes with different axial ligands, called cobaloximes.

CoCl2·6H2O (242 mg, 1mmol, 1 eq) was dissolved in abs EtOH. Pyridine (162 µL, 2 mmol, 2 eq) was then added to the ethanolic cobalt solution. This was left to stir at 293K for approximately 3 hours. A colour change was noted after one hour from the previous dark blue to a much paler translucent blue. A precipitate was also noted on the side of the round bottom at this time. The final solution was filtered via vacuum filtration and produced a purple powder which was washed with Diethyl ether. This powder was recrystallised in Abs EtOH (118% yield of crystals)

The [CoCl2(Py)2] is also a monomer which undergoes a polymerisation, I proposed the chlorido ligands act as bridging ligands to undergo a step growth mechanism but not 100% sure if that would be the correct mechanism or structure.

You can actually tell the geometry they adopt based on the colour, the purple is the octahedral polymer, and it turns blue when it’s a tetrahedral structure. I swapped the pyridine for alpha picoline and it only formed the tetrahedral structure due to the steric hindrance of the methyl group.
https://www.reddit.com/r/chemistry/comm ... _crystals/