in tetrahydrofuran S compd. added under Ar or N2 to a soln. of the Ge compd. in THF, mixt. stirred at 25°C for 6 h; mixt. concd. to 5 ml, cooled to -20°C, ppt. filtered, solvent evapd., fractional crystn. from ether/hexane (1:2), recrystd. from ether/hexane (1:5);