A parmagnetic nuclear magnetic resonance study of the lanthanide complexes [Ln(S2PMe2)4]–. Determination of phosphorus hyperfine coupling and solution structures

Abstract

The complexes [AsPh4][Ln(S2PMe2)4] have been prepared and their 1H and 31P n.m.r. spectra recorded at room temperature. The proton isotropic shifts are pseudo-contact in origin. The 31P shifts contain both contact and pseudo-contact contributions. The method used to separate the two contributions is described and demonstrates a change in solution structure at Ln = Dy. The change in structure is associated with a reduction in the hyperfine coupling to phosphorus from 1.09 to 0.51 MHz. For the heavy ions the relative phosphorus pseudo-contact shift falls almost to zero (–2.4 versus 32.0). The results are consistent with a change in structure from dodecahedral to square-antiprismatic.