Synthesis and structural characterization of discrete mono-, bi-, tri- and tetranuclear complexes of cadmium(II) with triphenylphosphoniopropionate

Five mono-, bi-, tri- and tetranuclear cadmium(II) complexes have been synthesized from the reaction of a tertiary phosphine betaine, Ph3P+(CH2)(2)CO2-, with various cadmium(II) salts, namely [Cd{Ph3P(CH2)(2)CO2}(4)(H2O)(2)](ClO4)(2) . 2H(2)O (1), [CdCl2-{Ph3P(CH2)(2)CO2}(2)] . 7H(2)O (2), [Cdl(2){Ph3P(CH2)(2)CO2}](2) (3), trans-Cd(H2O)(4)[Cl2Cd(mu-Cl){Ph3P(CH2)(2)CO2}](2) . 4H(2)O (4) and [Cd2Br4{Ph3P(CH2)(2)CO2}(2)](2) . dmf (5). In complex 1 the cadmium(II) atom is located at an inversion center, and is coordinated in a nearly perfect CdO6 octahedron with four unidentate betaine ligands defining the equatorial plane and two trans aqua ligands occupying the axial positions. Complex 2 exists as discrete mononuclear species which are linked by donor hydrogen bonds from the solvated water molecules to form a layer structure. Complex 3 is a discrete dimer in which the betaine ligands act in both one-atom bridge and bidentate chelate modes. Complex 4 comprises linear trimers which are joined by hydrogen bonds involving the chloro and aqua ligands and solvated water molecules to form a layer structure. Complex 5 is a novel tetranuclear molecule in which two of the four betaine ligands act in a very unusual mu(3) bridging mode.