Strukturchemie von Verbindungen des pentakoordinierten Siliciums. Das Bis(ethylendioxy)methylsilan-Anion / Structural Studies of Pentacoordinate Silicon. The Bis(ethylenedioxy)methylsilane Anion

Hexamethylendiammonium-bis(ethylenedioxy)methylsilane crystallizes in the hexagonal space group P6122, Z = 6 with a= 11.902(1), c = 30.148(4) A. The structure was refined to R - 0.041 using 2281 independent reflections. The geometry around the pentacoordinate silicon atom is between a trigonal bipyramid and a square pyramid. Oeq-Si-Oeq 136.0(1)°, Oax-Si-Oax 161.7(1)°. The Si-Oax bond lengths are 1.749(2) and 1.769(2) A, the Si-Oeq 1.711(2) and 1.735(2) A, Si-Ceq 1.876(3) A. The compound forms strong N-H ··· O hydrogen bonds between cation and anion. The cation lies on a crystallographic twofold axis