Solution and solid-state structures of lanthanide nitrate complexes with [(MeO)2P(O)]2C(OH)R (R=Me, tBu)

The complexes Ln(NO3)3La 2 (La=[(MeO)2P(O)]2C(OH)Me; Ln=La–Er) and Ln(NO3)3Lb 2 (Lb=[(MeO)2P(O)]2C(OH)tBu); Ln=La–Lu) have been synthesised. The solid-state structures examined by IR spectroscopy, single crystal X-ray diffraction and extended X-ray absorption fine structure show uniformity across the series up to Dy, the metal being ten coordinate. Solution structures have been examined by 31P NMR spectroscopy, conductivity, electrospray mass spectrometry and EXAFS, and results indicate that solution structures fall into two groups, one for the lighter (La–Sm) and one for the heavier (Eu–Lu) lanthanides. This structural change involves the diphosphonate ligands, which appear to be monodenate for the heavier metals, affording these a coordination number of eight.