Structural studies in metal-purpurate complexes. Part 8. Crystal structure of triaquapurpuratocalcium nitrate dihydrate

The crystal structure of the title compound, [CaL(H₂O)₃][NO₃]·2H₂O (L = purpurate), has been determined at 295 K by X-ray diffraction and refined by least squares to R 0.050 (1 545 'observed' reflections). Crystals are monoclinic, space group Pn, a = 11.282(5), b = 9.111(3), c = 9.045(4) Å, β = 105.70(3)° Z = 2. Co-ordination about the calcium is approximately eight-co-ordinate dodecahedral. One of the trapezoidal planes comprises the usual tridentate purpurate site [Ca-O, 2.567(4), 2.429(4); Ca-N, 2.600(5) Å] and a further purpurate bridging oxygen [Ca-O, 2.361(5) Å] while the other comprises the three co-ordinated water molecules [Ca-O, 2.372(7), 2.378(5), 2.460(5) Å] and another bridging purpurate oxygen [Ca-O, 2.548(6) Å], an infinite polymer resulting parallel to bc. The geometry within the nitrate isvery asymmetric [N-O, 1.213(10)-1.282(14) Å, O-N-O, 115.7(8)-122.9(8)°], and is found to correlate closely with the observed hydrogen bonding about the nitrate.