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).