Difluorosilanethione F 2 Si=S (1) has been synthesized by matrix IR spectrum. Ab initio calculations at the MP2 and CCSD(T) levels using large basis sets have been performed. Flash Vacuum Pyrolysis of (F 3 Si) 2 S at Ն 500 °C and trapped in an Ar matrix. Furthermore, 1 has been obtained by co-These calculations have guided the detection of 1 and the vibrational assignment. The best estimate of the structure of deposition of SiS and F 2 /Ar and by pyrolysis of a matrixisolated SiS 2 -XeF 2 complex under cryogenic conditions. All 1 with C 2v symmetry is: r(Si=S) 191.1(1) pm, r(SiF) 156.1(1) pm, Є(FSiF) 103.3(2)°. six vibrational fundamentals of 1 have been observed in the Our knowledge of molecular species exhibiting multiple uum thermolysis (FVT) of the cyclotrimer (4) and of other organosilicon precursors. [13] However, attempts to synthe-bonds to silicon has expanded greatly over the past 20 years due to both experimental progress and improvements in size the unsubstituted parent species H 2 SiϭS by FVT of different precursors failed, and only the dehydrogenation theoretical methods. Above all, kinetic stabilization by bulky substituents at both sites of SiϭSi, SiϭC, and product SiS has been observed. The present investigation adds to the limited list of unsta-SiϭPn (Pn ϭ N, P, As) linkages has enabled the synthesis and isolation of numerous compounds that are thermally bilized monomeric, four-atom silanethiones by describing F 2 SiϭS (1). We report on the synthesis of this species by stable up to, and even above, room temperature and possess "formally" double bonded silicon atoms. However, chalcog-FVT of (F 3 Si) 2 S (2). The unambiguous synthesis of the latter is also reported here for the first time. Alternatively, 1 eno derivatives R 1 R 2 SiϭCh, with Ch ϭ O, S, etc., provide only the silicon site to accommodate bulky substituents, can be made in analogy to Cl 2 SiϭS by the action of F 2 on SiS under cryogenic conditions. High-level ab initio cal-and it is not surprising that the first kinetically stabilized thioxosilane (silanethione ) that is stable at ambient tem-culations, which guided the detection and support the characterization of 1 by matrix IR spectroscopy, will also perature was made only recently. [5] Monomeric silanones and silanethiones with trigonal be presented. planar geometry at silicon are kinetically unstable due to [a] Anorganische Chemie, FB9, Universität-GH, D-42097 Wuppertal, Germany ation to yield the silylene HSiϪSH, are unlikely to occur