Structural studies in metal–purpurate complexes. Part 7. Crystal structures of diaquanitratopurpurato-cobalt(II) and -zinc(II) dihydrat

Abstract

The crystal structures of the title compounds, [ML(NO₃)(H₂O)₂]·2H₂O [L = purpurate, M = Co (1) or Zn (2)], have been determined at 295 K by X-ray diffraction and refined by least squares to R 0.058 (1 117 ‘observed’ reflections) and 0.078 (1 995 ‘observed’ reflections) respectively. Crystals are monoclinic, space group A2/a Z= 8. For (1), a= 26.86(4), b= 7.20(1), c= 16.774(6)Å, β= 101.65(9)°; for (2), a= 26.781(7), b= 7.192(2), c= 16.746(4)Å, β= 101.42(2)°. The isostructural complexes comprise a complex molecule with a tridentate purpurate ligand [M–N, 2.200(7)(1), 2.229(7)(2); M–O, 2.114(7), 2.112(6)(1), 2.104(7), 2.127(7)Å(2)] and an asymmetrically bidentate nitrate group in an approximate central plane [M–O, 2.384(8), 2.254(7)(1); 2.511(8), 2.266(8)Å(2)] with two water molecules axial [M–OH₂, 2.146(8), 2.060(9)(1); 2.138(8), 2.014(9)Å(2); O–M–O, 168.8(3)(1); 162.5(3)°(2)]. Very little difference is found in the geometries of the two molecules, the only non-trivial change being in the degree of asymmetry found in the nitrate co-ordination.