Crystal Structure of Calcium Picrate Pentahydrate: A New Eight-Coordinate Stereochemistry for [M(bidentate)₂(unidentate)₄]

Abstract

The crystal structure of the title compound, Ca(C₆H₂N₃0₇)₂,5H₂O, has been determined by single-crystal X-ray diffraction at 295(1) K and refined by least squares to a residual of 0.049 for 1513 'observed' reflections. Crystals are orthorhombic, Pmab, a 24.169(6), b l0.292(7), c 8.554(2) Å, Z 4. The stereochemistry about the calcium has not been observed previously for the system [M(bidentate)_2- (unidentate)₄]; in the present structure, the calcium is coordinated by a pair of bidentate picrate ligands and the four water molecules in an array in which three of the water molecules occupy a triangular face of a square antiprism, the overall array having m symmetry. The remaining water molecule occupies a lattice site with no close interaction with the other species.