Alkali-metal complexes. Part VII. Crystal and molecular structures of the o-nitrophenolatobis(1,10-phenanthroline) complexes of sodium and rubidium

Abstract

The structures of the title complexes have been determined by X-ray analysis from diffractometer data. The sodium complex has triclinic crystals, a= 10·436(6), b= 10·062(6), c= 14·867(7)Å, α= 96·98(2), β= 104·02(1), γ= 119·12(4)°, and its structure was determined by direct methods. The rubidium complex, isostructural with the corresponding potassium and caesium complexes, is also triclinic, a= 11·413(6), b= 13·214(6), c= 10·068(15)Å, α= 99·06(5)β= 114·80(5), γ= 101·78(3)°; this structure was determined from Patterson and electron-density maps. The structures were refined by least-squares methods to R 0·074 (Na complex, 1371 observed reflections) and 0·051 (Rb complex, 2107 observed reflections).

In the sodium complex, the cation is six-co-ordinate, interacting with the three chelating ligands in pseudo 32 symmetry, and the crystal structure of this complex is of monomeric units. The rubidium complex has a similar pseudo-three-fold symmetry of the chelating ligands but, with a larger co-ordination sphere, the cation also accepts co-ordination with a second o-nitrophenolate ion, which thus bridges cations about a centre of symmetry. Dimeric units, bound by van der Waals' forces, form the crystal structure. The packing arrangements in both complexes appear to depend on the interactions of overlapping phenanthroline molecules about centres of symmetry.

The phenanthroline molecules in both complexes have similar dimensions: all are non-planar, but there is no characteristic pattern of bending or twisting. The cations are displaced from the mean planes of the phenanthroline molecules by up to 0·63 Å. In the o-nitrophenolate ions, the variations in bond lengths and angles in the ions are significant and are explained in terms of resonance structure and second-order hybridisation effects. The nitro-groups are rotated about the C–N bonds by 18·6 (Na) and 14·5°(Rb).