Complexes of triphenylphosphine oxide with lanthanide bromides

The reaction between hydrated lanthanide bromides and triphenylphosphine oxide in 1:3 and 1:4 ratios in ethanol gave a series of complexes [LnBr2(Ph3PO)4]Br (Ln = Pr, Nd, Gd, Tb, Er, Yb, Lu) which contain ethanol and water in the lattice, regardless of the ratio of reactants used. The single crystal X-ray structures of [NdBr2(Ph3PO)4]Br, [GdBr2(Ph3PO)4]Br and [YbBr2(Ph3PO)4]Br have been determined and have an octahedral geometry about the metal ion. Analysis of the bond distances shows that the Ln–O and Ln–Br distances change in accord with the lanthanide contraction, but the non-bonded Ln⋯P distances and the Ln–O–P angles differ significantly for the Yb complex. Conductivity and variable temperature 31P NMR measurements in dichloromethane indicate that the complexes dissolve as [LnBr2(Ph3PO)4]+ for the lighter lanthanides with further ionisation becoming progressively more important for the heavier metals. In methanol more extensive dissociation is apparent. The electrospray mass spectra obtained from methanol solution show [LnBr2(Ph3PO)4]+ is present in high abundance in the gas phase with other species formed due to ligand redistribution, ionisation and solvolysis.