Solid-state NMR of tin, lithium and phosphorus compounds

Abstract

NMR spectroscopy is a powerful technique that allows the study of short-range electronic effects and local structure. The aim of the work has been to separate and manipulate the many different interactions so that they can be individually measured. For this we have used multinuclear techniques and probes. We have measured a range of spectra for different organotin, iminophosphorane and lithium compounds. We have obtained a selection of spectra including (^19(F and doubly-decoupled (^119)Sn for the organotin fluorides (^n)Bu(_3)SnF, Mes(_3)SnF, SnF(_2), Me(_2)SnF(_2), and (^n)Bu(_2)SnF(_2). These have been used to calculate the effective shielding anisotropies, asymmetries, effective dipolar coupling (D'), and the anisotropy in the indirect coupling (∆J), using analyses of the spinning-sideband manifolds. Simulation programs have been written to simultaneously fit multiple sets of data, which reduce the fitting errors and give the relative orientations of the tensor interactions. The (^19)F chemical shifts, indirect coupling (^1)j(SnF) and (^1)∆J(SnF) data have been summarised. For (^n)Bu(_2)SnF(_2), a structure has been proposed based on comparisons with the NMR results from the other compounds. For the iminophosphoranes, the dipolar tensor and its orientation can be measured from the (^31)P static spectrum, whilst in the MAS spectrum residual dipolar coupling lineshapes are visible. These give information about the electric dipole nature of the P-N bond and the nature of its bonding. For the lithium nuclei, the quadrupolar interaction is small, but can be directly studied. With the two NMR-active isotopes both tire shielding and quadrupolar interactions can be measured. Ab initio calculations have been used to calculate certain NMR parameters such as the shielding, quadrupolar and indirect coupling tensors from the molecular structure. Experimental data have been compared against tlie calculations to verify the accuracy of the model. At present, there is good agreement between experimental and calculated results for (^6,7)Li, (^13)C, (^14,15)N and (^31)P, though (^119)Sn remains a challenge.