A paramagnetic nuclear magnetic resonance study of the lanthanide complexes [Ln(S 2PR 2) 4] −, R = OMe, OPr i. Determination of phosphorus hyperfine coupling and solution structures

Abstract

The 1H and 31P NMR spectra of the complexes [AsPh 4][Ln(S 2PR 2) 4] for R = OMe, OPr i have been recorded at room temperature. The proton isotropic shifts are pseudocontact in origin. The total 31P isotropic shifts have been factored into their contact and pseudocontact contributions. The method used to separate the contact and pseudocontact shifts demonstrates a change in solution structure at Ln = Ho. The change in structure is associated with a reduction in the hyperfine coupling to phosphorus from 1.68 to 0.82 MHz (OMe), and from 1.57 to 0.85 MHz (OPr i. The relative phosphorous pseudocontact shifts falls from 31.7 for the light ions to 3.0 for the heavy ones (OMe), from 16.4 to 0.55 (OPr iCH) and from 57.1 to 1.84 (Opr iCH 3. These results are consistent with a change in structure of the coordination polyhedron from dodecahedral to square antiprismatic.