cis-Bis(2,2′-bipyridine-κ2 N,N′)dichloridocobalt(II) trihydrate

In the title complex, [CoCl2(C10H8N2)2]·3H2O, the Co(II) ion is situated on a twofold rotation axis and exhibits a slightly distorted octahedral geometry and is chelated by four N atoms of the two bidentate 2,2′-bipyridine ligands and two Cl− ions. The crystal packing is stabilized by hydrogen bonding formed between chloride ions and adjacent water molecules. One of the two independent water molecules in the asymmetric unit is disordered over two sets of sites, each on a twofold rotation axis, in a 0.734 (17):0.269 (17) ratio.

In the title complex, [CoCl 2 (C 10 H 8 N 2 ) 2 ]Á3H 2 O, the Co(II) ion is situated on a twofold rotation axis and exhibits a slightly distorted octahedral geometry and is chelated by four N atoms of the two bidentate 2,2 0 -bipyridine ligands and two Cl À ions. The crystal packing is stabilized by hydrogen bonding formed between chloride ions and adjacent water molecules. One of the two independent water molecules in the asymmetric unit is disordered over two sets of sites, each on a twofold rotation axis, in a 0.734 (17):0.269 (17) ratio.

Related literature
For the antibacterial activity of similar complexes, see: Senthilkumar & Arunachalam (2008). For similar complexes applied in the immunoassay of carcinoma antigen-125, see: Shihong et al. (2009). For the application of similar complexes as biosensors, see: Ying et al. (2006).

D-HÁ
The cobalt(II) ion has site symmetry 2 and assumes octahedral geometry with two symmetry related 2,2'-bipyridine ligands and two chloride ions. Cobalt(II) is linked to two 2,2'-bipyridine bidentate ligands via four nitrogen atoms and two chloride ions. The two 2,2'-bipyridine ligands are in cis position with mutually perpendicular to each other. The hydrated water molecules in the crystal packing helps the stabilization of crystal packing by forming hydrogen bonding between adjacent chloride ions.

Experimental
The complex was prepared by adding a solution of 2,2'-bipyridine (0.01 mole) in 60 ml of acetone, to a solution of cobalt(II) chloride (0.005 mole) in 60 ml of acetone. The resulting solution was stirred for two hours, filtered and dried over vacuum desiccator to get red colour complex (yield 90%). The dark red colored crystals, suitable for x-ray analysis, were obtained by slow evaporation from alcoholic solution.

Refinement
There is 1.5 water molecules per asymmetric unit. The H atoms of water oxygen O1 could be located in difference Fourier map. These H atoms were restrained to be at a distance of 0.85 Å from O1. The inter hydrogen distance was restrained to be 1.388 Å so as to retain the tetrahedral H-O-H angle. The other half molecule was disordered in two positions (O2 and O3). Their occupancies were refined initially as free variables and later the sum of the occupancies restrained as 0.5.
The H atoms of disordered water molecules could not be located. The aromatic H atoms were constrained as riding atoms with d(C-H) = 0.93 Å and U iso (H) = 1.2U equ (C). Fig. 1