Tin tetrachloride adducts with phosphoryl ligands: A DFT study

Tin tetrachloride adducts of the type SnCl4·2L (L = (Me2N)3P(O) (1), (Me2N)2P(O)F (2), Me2NP(O)F2 (3) and P(O)F3 (4)) have been theoretically studied by means of DFT geometry optimisation (B3LYP/LANL2DZ) and 119Sn chemical shift calculations (B3LYP/SV). A good correlation was found between calculated and experimental data. On going from complex 1 to 4, the SnL bond underwent considerable lengthening, while that of SnCl was shortened (SnO: 2.11 in cis-1 vs. 2.37 Å in cis-4; SnCl: 2.43 in cis-1 vs. 2.37 Å in cis-4). In the same way, the SnOP bond angle was found to decrease from 147° for cis-1 to 136° for cis-4. The trends are in good agreement with the calculated metal-ligand binding energies of complexes 1-4. Interestingly, the structural changes are accompanied by increased 119Sn chemical shifts towards higher frequencies as the Me2N groups in the ligand are substituted by fluorine atoms. The theoretical results showed that the use of the all-electron SV basis set for tin, together with the 6-31G∗ basis set for the other atoms could efficiently predict the 119Sn NMR chemical shifts in the complexes SnCl4·2L.