1. Presented in parts at the bi-ennial meeting of the Austrian Chemical Society (V�Ch), Graz (Austria), October 1979.
2. W. Traube, Ber. dtsch. chem. Ges.26, 607 (1893).
3. E. Nachbaur undA. Popitsch, Angew. Chemie85, 355 (1973).
4. Due to lack of reliable X-ray data this compound is not considered here.
5. E. Nachbaur, A. Popitsch, andP. Burkert, Mh. Chem.105, 822 (1974).