Tetrakis(triphenylphosphine oxide) complexes of the lanthanide nitrates; synthesis, characterisation and crystal structures of [La(Ph 3PO) 4(NO 3) 3]·Me 2CO and [Lu(Ph 3PO) 4(NO 3) 2]NO 3

Abstract

The reaction of Ln(NO 3) 3·6H 2O (Ln=La, Ce, Pr or Nd) with a sixfold excess of Ph 3PO in acetone formed [Ln(Ph 3PO) 4(NO 3) 3]·Me 2CO. The crystal structure of the La complex shows a nine-coordinate metal centre with four phosphine oxides, two bidentate and one monodentate nitrate groups, and PXRD studies show the same structure is present in the other three complexes. In CH 2Cl 2 or Me 2CO solutions, 31P NMR studies show that the complexes are essentially completely decomposed into [Ln(Ph 3PO) 3(NO 3) 3] and Ph 3PO. Similar reactions in ethanol gave [Ln(Ph 3PO) 3(NO 3) 3] only. In contrast for Ln=Sm, Eu or Gd, only the [Ln(Ph 3PO) 3(NO 3) 3] are formed from either acetone or ethanol solutions. For the later lanthanides Ln=Tb–Lu, acetone solutions of Ln(NO 3) 3·6H 2O and Ph 3PO gave [Ln(Ph 3PO) 3(NO 3) 3] only, even with a large excess of Ph 3PO, but from cold ethanol [Ln(Ph 3PO) 4(NO 3) 2]NO 3 (Ln=Tb, Ho–Lu) were obtained. The structure of [Lu(Ph 3PO) 4(NO 3) 2]NO 3 shows an eight-coordinate metal centre with four phosphine oxides and two bidentate nitrate groups. In solution in CH 2Cl 2 or Me 2CO the tetrakis-complexes show varying amounts of decomposition into mixtures of [Ln(Ph 3PO) 3(NO 3) 3], [Ln(Ph 3PO) 4(NO 3) 2]NO 3 and Ph 3PO as judged by 31P{ 1H} NMR spectroscopy. The [Ln(Ph 3PO) 3(NO 3) 3] also partially decompose in solution for Ln=Dy–Lu, forming some tetrakis(phosphine oxide) species.