Complexes of Lanthanide Nitrates with Tri-isopropylphosphine Oxide

The complexes formed on reaction of triisopropylphosphine oxide ((C3H7)3PO = L) and lanthanide nitrates have been studied. The new compounds have been characterised by elemental analysis, infrared and 31P NMR spectroscopy in CD2Cl2 solution. On reaction of lanthanide nitrates and L in 1:3 ratios, well defined Ln(NO3)3L3 are obtained for Ln = La – Eu with complexes for the heavier lanthanides forming mixtures of Ln(NO3)3L3 and Ln(NO3)3L2. Analytically pure complexes Ln(NO3)3L2 can be isolated for Yb and Lu. Single crystal X-ray structures for Ln(NO3)3L3, Ln =La (1), Ce (2), Pr (3), the ionic complex [Er(NO3)2L3(H2O)][NO3] (4) and Ln(NO3)3L2, Ln = Yb (5), Lu (6) are reported. The 31P solution NMR spectra of Ln(NO3)3L3 show that the complexes are fluxional at ambient temperature with spectra consistent with static structures observed at lower temperatures for some complexes. The structures and solution properties are discussed in terms of the steric and electronic properties of the ligand.