The synthesis, spectroscopic characterization, and crystallographic study of the tetra-phenylimido-diphosphinates of Sc, Y, La, and Lu

Abstract

In the present study, we report the synthesis, spectroscopic characterization, and X-ray single crystal structural determination of four rare earth complexes, M[Ph2P(O)NP(O)PPh2]3, M = Sc, Y, La, and Lu. The structural study reveals that the Sc, Y, and Lu complexes have coordination numbers of six, while the La complex shows a coordination number of seven, through the presence of the additional coordination of a water molecule with a square-face-capped geometry, where the water molecule enables the formation of a dimeric structure through OH…O hydrogen bond interactions. The metal ions M3+, Sc, Y, La, and Lu are coordinated to the [Ph2P(O)NP(O)Ph2]− ligand with a delocalized phosphazenic PNP system in an O,O isobidentate manner, generating carbon-free metallo-inorganic six-membered rings, of which one acquires the a (anti-parallel) conformation and the other two the twist-boat conformation. The Y and Lu complexes crystallized with similar unit cells, M…O distances, and O…M…O angles that are consequences of their similar crystal radii related to the lanthanide contraction in Lu, while the La complex has a coordination number of seven through the coordination of a water molecule and a square-face-capped geometry. The O-M-O angles in the complexes suggest that the bite of the ligand depends on the size of the metal ion, the flexibility, and the steric effects of the tetra-phenyl-imidodiphosphinate ligand.