Hexaaquacobalt(II) bis(2,2′-sulfanediyldiacetato-κ3 O,S,O′)cobaltate(II) tetrahydrate

The two CoII atoms in the title salt, [Co(H2O)6][Co(C4H4O4S)2]·4H2O, exist in an octahedral coordination environment. In the cation, the Co atom is surrounded by six water molecules, and in the anion, it is bis-O,S,O′-chelated by the thioacetate ligands. The cations, anions and uncoordinated water molecules are linked by O—H⋯O hydrogen bonds into a three-dimensional network.

The two Co II atoms in the title salt, [Co(H 2 O) 6 ][Co(C 4 H 4 -O 4 S) 2 ]Á4H 2 O, exist in an octahedral coordination environment. In the cation, the Co atom is surrounded by six water molecules, and in the anion, it is bis-O,S,O 0 -chelated by the thioacetate ligands. The cations, anions and uncoordinated water molecules are linked by O-HÁ Á ÁO hydrogen bonds into a three-dimensional network.

Experimental
Data collection: RAPID-AUTO (Rigaku, 1998); cell refinement: RAPID-AUTO; data reduction: CrystalClear (Rigaku/MSC, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: publCIF (Westrip, 2010 First-row transition metal dications form a plethora of metal dicarboxylates; in some cases, a a direct metal-carboxylate bond is formed and in other cases, the product consists of hexaaquametal cations and carboxylate ions, the anion interacting indirectly in an outer-sphere type of coordination. Thioacetic acid yields several metal carboxylates; the reaction of the deprotonated acid with cobalt(II) ions gives the hexaaquacobalt(II) di(carboxylato)cobaltate(II) (Scheme I, Fig. 1). The two Co II atoms in the salt exist in octahedral coordination environments. That in the cation is surrounded by water water molecules; that in the anion is O,S,O'-chelated by the thioacetate ligands. The cations, anions and lattice water molecules are linked by O···H···O into a three-dimensional network ( Table 1). The salt is isostructural with the nickel(II) analog (Pan et al., 2005).

Experimental
Cobalt diacetate (1 mmol) was added to an aqueous solution of thiodiacetic acid acid (1 mmol) that was earlier been treated with 1M sodium hydroxide to a pH of 6. The filtered solution was set aside for several days, after which pink prismatic crystals separated from solution.

Refinement
Carbon-bound H-atoms were placed in calculated positions (C-H 0.93 Å) and were included in the refinement in the riding model approximation, with U(H) set to 1.2U(C). The water H-atoms were located in a difference Fourier map, and were refined with distance restraints of O-H 0.84±0.01 Å and H···H 1.37±0.01 Å; their U values were set to 1.5U eq (O).
The anisotropic displacement ellipsoids of the lattice water O atoms were restrained to be nearly isotropic.