Nuclear spin–spin coupling to89Y. A model to investigate the question of covalent bonding in lanthanoid dithiophosphinate complexes

The observation of spin–spin coupling between 89Y and 31P nuclei in the complex [Y(S2PR2)4]–, R = OEt, is interpreted as evidence for covalent bonding. The magnitude of the reduced coupling constant 2KY–P is of the same order as 2KRh–P and 2KPt–P in [Rh(S2PR2)3] and [Pt(S2PR2)2] indicating similarity in the covalent contribution to their bonds. This result is extrapolated to the chemically similar lanthanoid complexes. The mechanism of hyperfine coupling in paramagnetic lanthanoid complexes, the nephelauxetic effect and the intensities of observed f–f transitions are discussed with respect to the above model.