Complexes of Lanthanide Nitrates with Tri Tert Butylphosphine Oxide

Reaction of lanthanide nitrates with ^tBu₃PO (=L) lead to the isolation of complexes Ln­(NO₃)₃L₂·H₂O·nEtOH (Ln = La (1), Nd­(2)), Ln­(NO₃)₃L₂ ·nEtOH (Sm­(3), Eu­(4)), and Ln­(NO₃)₃L₂ (Dy­(5), Er­(6), Lu­(7)). These have been characterized by elemental analysis, infrared and NMR­(¹H, ¹³C and ³¹P) 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° 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° and the nitrate ligands coplanar giving a hexagonal bipyramidal geometry. These isomers cannot be observed by variable temperature solution ³¹P 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 °C. Attempts to prepare cationic species [Ln­(NO₃)₂L₃]⁺[PF₆]⁻ have not been totally successful and led to the isolation of crystals of Lu­(NO₃)₃L₂ and Tb­(NO₃)₃L₂.CH₃CN (8).