We report here the characterization in solution (NMR, luminescence, MS) and the solid-state (X-ray crystallography, IR) of complexes between phenacyldiphenylphosphine oxide and five Ln(iii) ions (Sm, Eu, Gd, Tb, Dy). Four single crystal X-ray structures are described here showing a 1 : 2 ratio between the Ln ions Eu, Dy, Sm and Gd and the ligand, where the phosphine oxide ligands are bound in a monodentate manner to the metal center. A fifth structure is reported for the 1 : 2 Eu(NO)-ligand complex showing bidentate binding between the two ligands and the metal center. The solution coordination chemistry of these metal complexes was probed by H,C and P NMR, mass spectrometry, and luminescence experiments. The title ligand has the capability to sensitize Tb, Dy, Eu and Sm leading to metal-centered emission in solutions of acetonitrile and methanol and in the solid state.

The title compounds were synthesized via an Arbuzov reaction between an α-bromo­ketone and isopropoxydi­phenyl­phosphane. In the crystals of both compounds, mol­ecules are linked via bifurcated C—H⋯(O,O) hydrogen bonds, forming chains propagating along [100] and along [010].