Lanthanide nitrate complexes with triethylphosphine oxide. Solid state and solution properties

Abstract

Complexes between lanthanide nitrates and triethylphosphine oxide have been prepared and fall into two distinct categories. With the lighter lanthanides Ln(NO3)3(Et3PO)3 (Ln=La, Ce, Pr, Nd, Eu) are formed whilst for the heavier metals mixtures of Ln(NO3)3(Et3PO)3 and Ln(NO3)3(Et3PO)2 are isolated. The structures of Ln(NO3)3(Et3PO)3 (Ln=La, Ce, Eu) have been determined by single crystal X-ray crystallography and show that all the complexes are 9-coordinate and have a pseudo mer-octahedral arrangement if the bidentate nitrates are envisaged as monodentate ligands. The conductivity in dichloromethane and acetonitrile indicates that the complexes are non-conducting. NMR spectra in CD2Cl2 solution are consistent with a rapid interconversions of the inequivalent phosphorus environments. For the Yb and Lu complexes static structures can be assigned to peaks in the low temperature 31P NMR spectra which also show evidence of a pseudo fac-isomer and a 1:2 complex. The formation of mixtures of 1:2 and 1:3 complexes for the heavier lanthanides is discussed in terms of the balance between steric effects and the basicity of the phosphine oxide ligands.