in acetone under Ar HgCl2 in acetone was added dropwise at 0°C over 1 h to soln. 1,3-bis(((dimethylisopropoxysilyl)methyl)diphenylstannyl)propane and stirred for 14 h at room temp.; soln. was filtered, solvent was removedin vacuo, residue was extd. with hot n-hexane, extract was kept overnight at -25°C, ppt. was filtered and dried;