Tetragonal silicon compounds

An asymmetric synthesis at silicon was developed starting from tetragonal silicon compounds. Prochiral compounds of type R1R2SiX2 having two enantiotopic functional groups X are of particular interest. Owing to the many stereospecific substitution reactions that can be performed at a functional silicon atom, the preparation of optically... 

These compounds are observed for the first fetv members of the rare earth series, and are of interest in shoving tetragonal symmetry, the unit cell of the cerium end-member having dimensions a = 1.014 and c = 0.484 nm. The 3-D linked arrangement of tetrahedra, tvith the rare earth atoms in the interstices (Figure 5.20), has more or less every nitrogen linked to two silicon atoms, as would be expected from the almost 1 2 ratio of Si N. 

One of the many families of intermetallic systems, which turned out to be particularly interesting, consists of compounds exhibiting the tetragonal BaAl type of crystal structure and its modifications. A few hundred of these compounds have been synthesized up to now and their properties investigated. Their general chemical formula is RT2X2, where R is a rare earth, T is a transition 3d, 4d, or 5d metal and X is silicon or germanium. 

---