Tetraaquabis(piperazin-1-ium)cobalt(II) bis(sulfate) dihydrate

In the centrosymmetric title compound, [Co(C4H11N2)2(H2O)4](SO4)2·2H2O, the CoII atom is coordinated in a distorted octahedral geometry by four water O atoms and two piperazinium N atoms. These four water O atoms define an equatorial plane with a maximum deviation of 0.0384 (1) Å while the two piperazinium N atoms complete the octahedron in the axial positions. Neighboring complex molecules and sulfate anions are connected through an extensive network of N—H⋯O and O—H⋯O hydrogen bonds, which link the different chemical species into layers in the ab plane. Additional Owater—H⋯O hydrogen bonds involving the non-coordinating water molecules and C—H⋯O interactions connect these layers into a three-dimensional supramolecular structure.

In the centrosymmetric title compound, [Co(C 4 H 11 N 2 ) 2 -(H 2 O) 4 ](SO 4 ) 2 Á2H 2 O, the Co II atom is coordinated in a distorted octahedral geometry by four water O atoms and two piperazinium N atoms. These four water O atoms define an equatorial plane with a maximum deviation of 0.0384 (1) Å while the two piperazinium N atoms complete the octahedron in the axial positions. Neighboring complex molecules and sulfate anions are connected through an extensive network of N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds, which link the different chemical species into layers in the ab plane. Additional O water -HÁ Á ÁO hydrogen bonds involving the non-coordinating water molecules and C-HÁ Á ÁO interactions connect these layers into a three-dimensional supramolecular structure.

Comment
In view of the importance of piperazines which are found in biologically active materials across a number of areas of therapeutic importance (Bogatcheva et al., 2006), the structural chemistry of metal salts that include piperazine and its derivatives does not cease to develop and continues to be a subject of research in many laboratories. Among the compounds investigated recently are several metal sulfate salts such as piperazinium hexaaquacobalt (II) disulfate (Pan et al., 2003), piperazinedium hexaaquazinc (II) bis sulfate (Rekik et al., 2005) and homopiperazin-1,4-diium bis-hexaaquacobalt (II) trisulfate (Sahbani et al., 2011), among others. In these structures the cobalt atoms are hexacoordinated by six water molecules, and the piperazinium cations are diprotonated and not metal coordinated. In this report, we would like to present the crystal structure of a sulfate salt of a cobalt-piperazinium complex, [Co(C 4  , and four oxygen atoms from the water molecules complete the coordination sphere of cobalt atom in the title compound. The piperazinium cation (C 4 H 11 N 2 ) + adopts a chair conformation as evidenced by the mean deviation (±0.0384 Å) from the least square plane defined by the four constituent atoms C1, C2, C3 and C4 and the remaining atoms N1 and N2 displaced from the plane by -0.6523 and 0.6392 Å, respectively. This is the so far only observed conformation for coordinated monoprotonated piperazines (19 entries in the Cambridge structural database with atom coordinates reported, database accessed Nov 2013 (Allen, 2002)).
Neighboring complexes and sulfate anions are connected through an extensive network of N-H···O and O-H···O hydrogen bonds, which link the different chemical species into two-dimensional layers in the ab plane (Fig.2). Additional OW-H···O hydrogen bonds that involve the not coordinated water molecules and C-H···O interactions connect these layers into a three-dimensional supramolecular structure.

Experimental
Piperazine (0.17g, 2 mmol) and cobalt acetate (0.24g, 1 mmol) were dissolved in 10 ml of water. The resulting solution was added to an aqueous solution of sulfuric acid (2 mmol, 2 ml). The mixture was stirred for 20 min at room temperature. After slow evaporation of the solvent over several days at ambient temperature, pink single crystals of the title compound suitable for X-ray diffraction formed in the solution.

Refinement
All H atoms bonded to C and N atoms were positioned geometrically and treated as riding on their parent atoms, [N-H = 0.89, C-H =0.97 Å with U iso (H) = 1.2 U eq (C,N), but those attached to oxygen atom were located in difference density fourier maps. O-H bond distances and distances between two H atoms from each water molecule were restrained to be 0.85 (2) and 1.37 (2) Å, with U iso (H) = 1.5 U eq (O).

Computing details
Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: CAD-4 EXPRESS (Enraf-Nonius, 1994); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012).   View of the atomic arrangement of the title compound along the b axis.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.73 e Å −3 Δρ min = −0.35 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.