Silicon compounds with donor atoms in geminal position have a lot of unusual properties as compared to those of the carbon analogues. The deviating properties include magnetic susceptibility, dipole moments, basicity, various spectroscopic parameters, reactivity and molecular structure. Such effects have often been described as the α-effect in silicon chemistry, but also germanium and tin chemistry.
These investigations are relevant for a fundamental understanding of the chemistry of geminal systems and heteroatom effects in silicon chemistry. Compounds with SiON units (silylhydroxylamines) are also important as silicone rubber cold curing catalysts and discussed as intermediates in catalytic reactions of SiH functions.
Our research in this field is the synthesis of simple model compounds containing an acceptor atom (Si, Ge, Sn) and a donor atom (N, O, P, S) linked by a spacer group.

Both types of aggregation (monomers and dimers) are found as illustrated by the following examples.

Crystal structure of F3SiONMe2	Folie

Crystal structure of F3SiCH2NMe2	Folie

We investigate systematically the factors determining the aggregation type and interaction strength such as substituent effects at donor, acceptor and spacer atom and the conformation of the molecules.

Crystal structure of (F3C)F2SiONMe2	Folie

Crystal structure of (F3Si)(Me3Si)NNMe2	Folie

Further extension of this research aims at the investigation of a broader range of acceptor A, spacer S and donor groups D. The following table shows some immediately obvious possibilities for combinations.

A Z D F3Si-, FH2Si-, F3CF2Si-, R3Si- F3Ge-, (F3C)3Ge-, R3Ge- F2P-, (F3C)2P-, R2P- F2As-, (F3C)2As-, R2As- F4P-, R4P- F4As -, R4As- F4Sb-, R4Sb- -CH2-, -CR2- -NR- -PR- -O- -S- -Se- -NR2 -PR2 -AsR2 -OR -SR