Structural diversity of four-co-ordinate metal(II) compounds with the bidentate bis(diphenylselenophosphoryl)amide ligand, [M{N(PPh₂Se)₂-Se,Se'}₂] (M=Sn, Pb, Zn, Cd or Hg)

The [N(PPh(2)Se)(2)](-) ion formed stable bis-chelates with M(II) (M = Sn, Pb, Zn, Cd or Hg), [M{N(PPh(2)Se)(2)-Se,Se'}(2)], which exhibit a large diversity of structural arrangements around the metal, as shown by X-ray crystallography. The tin(II) complex crystallises dimorphically, as yellow triclinic prisms (1) and red tetragonal octahedrons (1'). The yellow isomer is square planar, representing the first example of a true square-planar tin(II) spiro-compound. The red isomer and the lead(II) compound (2) exhibit a distorted psi-trigonal-bipyramidal co-ordination geometry with a vacant equatorial position, which suggests the presence of a stereoactive electron lone pair. The cadmium(II) and mercury(II) complexes (3 and 4) are tetrahedral.