Stereochemisty of rigid chelate–metal complexes. Part 4. Crystal structures of tetra-aquabis(1,10-phenanthroline)strontium(II) perchlorate– and tetra-aquabis(1,10-phenanthroline)barium(II) perchlorate–1,10-phenanthroline(1/2)

Abstract

The crystal structures of the title complexes, [Sr(phen)2(OH2)4][ClO4]2·2phen (1) and [Ba(phen)2(OH2)4][ClO4]2·2phen (2), have been determined by X-ray diffraction from diffrectometer data and refined by least squares to R 0.120(1) and 0.13(2) for 1 423 and 2 478 observed reflections respectively. The two complexes are similar. Crystals are triclinic, space group P with Z= 1 in unit cells of dimensions: (1)a= 1 344.4(4), b= 1 268.4(4), c= 706.8(2) pm, α= 99.31 (2), β= 92.55(2), γ= 76.21 (3)°; (2)a= 1 336.9(1), b= 1 300.3(b), c= 703.2(1) pm, α= 100.01(2), β= 95.15(1), γ= 75.53(2)°. The metal ions have an eight-co-ordinate distorted cube stereo-chemistry involving four nitrogens from two phenanthroline ligands and four oxygens from water molecules.The trans-related phens pack almost parallel to ab plane containing also the metal, while the remaining phen pair, also parallel to ab but not bonded to the metal, are merely ‘sandwiched’ in the structure halfway between the metal centres, along the c axis. The point-group symmetry of the metal complex unit is approximately C2h. There appear to be no bonding forces holding the ‘floating’ phens in the structure, the shortest contact, N ⋯ H–O (to water), being 359 (1) and 378 pm (2). The bonded waters are also independent of the perchlorateanions, the closest contact being 326 and 340 pm. The perchlorate groups are disordered to the extent that the centre of symmetry in the otherwise centric complex is destroyed by a completely dissymmetric tetrahedral arrangement of oxygens.