Raman and UV-VIS study of the conformational polymorphism of solid tetramesityldisilene Mes2Si=SiMes2

All three modifications of tetramesityldisilene 1 reported to date (orange unsolvated 1a and two yellow 1:1 solvates with toluene 1b and THF 1c) have been shown to readily transform to a new form, yellow unsolvated 1d, for which a quasi-trans conformation with two mesityl rings nearly orthogonal and the other two nearly coplanar to the double bond plane, is tentatively proposed. Form 1d appears to be the most stable conformational polymorph, but can be converted to the orange form upon illumination in the region 514–457 nm.