Complexes of Lanthanide
Nitrates with Tri Tert Butylphosphine
Oxide
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Abstract
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>)