Cerium(IV) Nitrate Complexes With Bidentate Phosphine Oxides

The reactions between ceric ammonium nitrate, (NH₄)₂Ce(NO₃)₆, (CAN) and the bidentate phosphine oxides, 4,5-bis(diphenylphosphine oxide)-9,9-dimethylxanthene (L¹), oxydi-2,1-phenylene bis(diphenylphosphine dioxide) (L²), 1,2-bis(diphenylphosphino)ethane dioxide (L³) and 1,4-bis(diphenylphosphino)butane dioxide, L⁴ have been investigated. The crystal structures of the molecular Ce(NO₃)₄L¹ ( 1 ), and ionic Ce(NO₃)₃L³₂]NO₃]?CHCl₃ ( 3 ), Ce(NO₃)₃L³₂]NO₃] ( 4 ) and the polymeric Ce(NO₃)₃L⁴_1.5] NO₃] ( 5 ) and the cerium(III) complex Ce(NO₃)₂L¹₂]NO₃] ( 2 ) are reported. The thermal stability of the complexes has been examined by thermogravimetry with the gaseous decomposition products analysed by infrared spectroscopy. Evolution of CO₂ is found for both Ce(III) and Ce(IV) complexes with the later also forming NO₂. The formation of the complexes in solution has been studied by ³¹P NMR spectroscopy and further complexes Ce(NO₃)₃L¹₂]⁺NO₃]^? and Ce(NO₃)₂L¹₃]²⁺2NO₃]^? identified in CD₃CN solution. The complex ( 1 ) exists as a single molecular species in solution and is stable in dichloromethane whilst ( 3 ) decomposes on standing in both CD₂Cl₂ and CD₃CN to Ce(III) containing species. Complexes of L² have been identified by solution ³¹P NMR spectroscopy and these decompose in solution to give Ce(NO₃)₃L²₂. This study represents the first structural characterisations of Ce(IV) complexes with bidentate phosphine oxides.