Spirocyclic tin salicyl alcoholates - a combined experimental and theoretical study on their structures, 119 Sn NMR chemical shifts and reactivity in thermally induced twin polymerization.

The spirocyclic tin salicyl alcoholate, 4H,4'H-2,2'-spirobi[benzo[d][1,3,2]dioxastannine] (1), and its 6,6'-dimethoxy (2) and 8,8'-di-tert-butyl-6,6'-dimethyl derivative (3) were synthesized and thermally induced twin polymerization of precursor 2 was performed to give a SnO2-containing hybrid material. Studies on the molecular structures of 1-3 were carried out using Sn-119{H-1} CP MAS NMR spectroscopy and DFT calculations. Crystallization of compound 3 from dimethyl sulfoxide solution provided the Lewis acid-base adduct 3(dmso)(2) exhibiting a hexacoordinated tin atom in the solid state, in agreement with the results of the spectroscopic and DFT calculation data. 119Sn NMR spectroscopy of the compounds 1-3 and 3 (dmso) 2 revealed equilibria among the diverse oligomers in solution phase pointing at hexacoordinated tin atoms.