Complexes of Lanthanide Nitrates with Tri Tert Butylphosphine Oxide

Reaction of lanthanide nitrates with <sup>t</sup>Bu<sub>3</sub>PO (=L) lead to the isolation of complexes Ln­(NO<sub>3</sub>)<sub>3</sub>L<sub>2</sub>·H<sub>2</sub>O·<i>n</i>EtOH (Ln = La (<b>1</b>), Nd­(<b>2</b>)), Ln­(NO<sub>3</sub>)<sub>3</sub>L<sub>2</sub> ·<i>n</i>EtOH (Sm­(<b>3</b>), Eu­(<b>4</b>)), and Ln­(NO<sub>3</sub>)<sub>3</sub>L<sub>2</sub> (Dy­(<b>5</b>), Er­(<b>6</b>), Lu­(<b>7</b>)). These have been characterized by elemental analysis, infrared and NMR­(<sup>1</sup>H, <sup>13</sup>C and <sup>31</sup>P) 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 <sup>31</sup>P 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(NO<sub>3</sub>)<sub>2</sub>L<sub>3</sub>]<sup>+</sup>[PF<sub>6</sub>]<sup>−</sup> have not been totally successful and led to the isolation of crystals of Lu­(NO<sub>3</sub>)<sub>3</sub>L<sub>2</sub> and Tb­(NO<sub>3</sub>)<sub>3</sub>L<sub>2</sub>.CH<sub>3</sub>CN (<b>8</b>).