Structure and optical properties of the planar silicon compounds polysilane and Wohler siloxene

The two-dimensional silicon backbone structure of planar polysilane and Wohler siloxene is responsible for their exciting luminescing properties. We have prepared single crystals of siloxene by a topotactic reaction from crystalline CaSi2. The chemical composition was determined as [Si6H3(OH)(3)](n) The x-ray crystal structure analysis identifies the so-called Wohler siloxene as 2D-poly[1,3,5-trihydroxocyclohexasilane]. Polysilane exhibits the same structural properties but with a chemical composition [Si6H6](n). The optical properties (infrared transmission, photoluminescence, excitation spectroscopy) of these well-defined materials are presented. A heat treatment above 350 degrees C in vacuum of Wohler siloxene results in a destruction of the planar (2)(infinity) [Si-] structure by internal rearrangements, which is evidenced by the x-ray-diffraction pattern and characteristic changes in the optical spectra. The involvement of Wohler siloxene in the optical properties of porous Si is critically reviewed.