Complexes of Lanthanide Nitrates with Tri Tert Butylphosphine Oxide

Reaction of lanthanide nitrates with (Bu3PO)-Bu-t (=L) lead to the isolation of complexes Ln(NO3)(3)L-2 center dot H2O center dot nEtOH (Ln = La (1), Nd(2)), Ln(NO3)(3)L-2 center dot nEtOH (Sm(3), Eu(4)), and Ln(NO3)(3)L-2 (Dy(5), Er(6), Lu(7)). These have been characterized by elemental analysis, infrared and NMR(H-1, C-13 and P-31) spectroscopy and single-crystal X-ray diffraction. The structures show L to be positioned on opposite sides of the metal with the nitrates forming an equatorial band. When Ln = Dy, Er, and Lu two distinct molecules are present in the unit cell. A major isomer (70%) has a (P)O-Ln-O(P) angle of less than 180 degrees with one of the nitrate ligands twisted out of the plane of the other nitrates while the lower abundance isomer is more symmetric with the (P)O-Ln-O(P) angle of 180 degrees and the nitrate ligands coplanar giving a hexagonal bipyramidal geometry. These isomers cannot be observed by variable temperature solution P-31 NMR measurements but are clearly seen in the solid-state NMR spectrum of the Lu complex. Variable temperature solid-state NMR indicates that the isomers do not interconvert at temperatures up to 100 degrees C. Attempts to prepare cationic species [Ln(NO3)(2)L-3](+)[PF6](-) have not been totally successful and led to the isolation of crystals of Lu(NO3)(3)L-2 and Tb(NO3)(3)L-2 center dot CH3CN (8).