NMR studies of ³¹P, ¹H spin pairs in solid tin(II) phosphite and tin(II) hydrogen phosphate

Abstract

We show how the spin dynamics in isolated spin systems presents both opportunities and complications, using the ¹H, ³¹P pair encountered in solid SnHPO₃ and SnHPO₄. Transient oscillations observed in the build-up of ³¹P magnetization, during cross-polarization under moderately fast magic-angle spinning, allow us to measure ³¹P and ¹H dipolar coupling constants. We show that this approach to determining internuclear distances (1.42 ± 0.01 Å for SnHPO₃ and 2.05 ± 0.03 Å for SnHPO₄) is particularly robust for strong dipolar couplings (of the order of the spin rate). These distances had not been determined in previous X-ray diffraction studies, due to the difficulty of locating the hydrogen atoms in the presence of Sn. We also show that the interaction of the ³¹P shielding tensor, ³¹P,¹H dipolar coupling and continuous-wave decoupling results in unusual line-splittings and broadenings in the {³¹P}¹H spectra. These effects are only partially suppressed by the use of more sophisticated decoupling methods.

Acknowledgments

We would like to thank Philip Waterfield (Unilever, Port Sunlight) for the SnHPO₃ sample. PA thanks the Royal Thai government for a studentship. One of us (RKH) thanks the Leverhulme Trust for an Emeritus Fellowship. We acknowledge the award of spectrometer time under the EPSRC Solid-state NMR Research Service based in Durham.