Abstract
Bis(diphenylphosphino)methane dioxide (dppmO2) forms eight-coordinate cations [M(dppmO2)4]Cl3 (M = La, Ce, Pr, Nd, Sm, Eu, Gd) on reaction in a 4:1 molar ratio with the appropriate LnCl3 in ethanol. Similar reaction in a 3:1 ratio produced seven-coordinate [M(dppmO2)3Cl]Cl2 (M = Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb), whilst LuCl3 alone produced six-coordinate [Lu(dppmO2)2Cl2]Cl. The complexes have been characterised by IR, 1H and 31P{1H}-NMR spectroscopy. X-ray structures show that [M(dppmO2)4]Cl3 (M = Ce, Sm, Gd) contain square antiprismatic cations, whilst [M(dppmO2)3Cl]Cl2 (M = Yb, Dy, Lu) have distorted pentagonal bipyramidal structures with apical Cl. The [Lu(dppmO2)2Cl2]Cl has a cis octahedral cation. The structure of [Yb(dppmO2)3(H2O)]Cl3·dppmO2 is also reported. The change in coordination numbers and geometry along the series is driven by the decreasing lanthanide cation radii, but the chloride counter anions also play a role.
Highlights
Work viewed the chemistry of the lanthanides (Ln) (Ln = La–Lu, Pm unless otherwise indicated) in oxidation state III as very similar and often only two or three elements were examined, and the results were assumed to apply to all
The main changes along the series are due to the lanthanide contraction, the reduction in the radius of the M3+ ions between La (1.22 Å) and Lu (0.85 Å), and at some point a reduction in coordination number may be driven by steric effects, especially with bulky ligands
We reported bis(diphenylphosphino)methane dioxide formed square-antiprismatic cations [La(dppmO2)4]3+ with Cl, I or [PF6] counter ions, but lutetium gave only octahedral [Lu(dppmO2)2X2]+ (X = Cl, I) and [Lu(dppmO2)2Cl(H2O)]2+ [8]
Summary
The decrease in radius results in an increase in the charge/radius ratio along the series and this can lead to significant electronic effects on the ligand preferences. This interplay of steric and electronic effects means that changes in coordination number or ligand donor set can occur at different points along the series with different ligands. Tertiary phosphine oxides have proved popular ligands to explore lanthanide chemistry and the area has been the subject of a comprehensive review [3], and several detailed studies of trends along the series La-Lu have been reported [4,5,6,7]. We report a systematic study of the systems LnCl3-dppmO2 for all fourteen accessible lanthanides
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