Bis(diphenylphosphino)methane dioxide complexes of lanthanide trichlorides: synthesis, structures and spectroscopy

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&middot
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.