Bis(2-aminobenzothiazol-3-ium) bis(7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylato-κ3 O 2,O 3,O 7)nickelate(II) hexahydrate

In the title compound, (C7H7N2S)2[Ni(C8H8O5)2]·6H2O, the NiII cation is located on an inversion center and is O,O′,O′′-chelated by two symmetry-related 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylate anions in a distorted octahedral geometry. The 2-aminobenzothiazol-3-ium cation links with the Ni complex anion via N—H⋯O hydrogen bonding. Extensive O—H⋯O and N—H⋯O hydrogen bonds involving the lattice water molecules also occur in the crystal structure.


Gui-Xian Wang, Qi-Wei Zhang and Fan Zhang
Comment 7-oxabicyclo[2,2,1]heptane-2,3-dicarboxylic anhydride (norcantharidin), which has been considered as potent inhibitor of the serine/threonine protein, has great anti-cancer activity (Hill et al., 2007). A isostructural manganese complex (Wang et al., 2010a) and a cobalt complex (Wang et al., 2010b) has been reported. The molecular structure of the title complex is shown in Fig.1. The nickel atom is six-coordinated in a distorted octahedral coordination mode, binding to two bridging O atoms of the bicycloheptane unit and four carboxylate O atoms of two symmetry-related and fully deprotonated ligands. 2-aminobenzothiazole don't involved the coordination, and N atom of thiazole ring is protonated.
The crystal structure is stabilized by N-H···O hydrogen-bonding interactions between the cations and anions and O-H···O hydrogen bonds including the crystal water molecules.

Experimental
A mixture of 0.5 mmol norcantharidin, 0.5 mmol nickel acetate, 0.5 mmol 2-aminobenzothiazole and 15 mL distilled water was sealed in a 25 mL Teflon-lined stainless vessel and heated at 443 K for 3 d, then cooled slowly to room temperature. The solution was filtered and block green crystals were obtained.

Refinement
The H atoms bonded to O atoms were located in a difference Fourier maps and refined with O-H distance restraints of 0.85 (3) Å and U iso (H) = 1.5U eq (O). Other H atoms were positioned geometrically and refined using a riding model with C -H = 0.97-0.98 and N-H = 0.86 Å, U iso (H) = 1.2U eq (C,N).  A view of the molecule of (I) showing the atom-labelling scheme with displacement ellipsoids drawn at the 30% probability.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.