The compound B8F1,, prepared by disproportionation of F,BBFBF,, has been characterised. It is believed t o be a structural analogue of diborane. It has been treated with electron-pair donors to give complexes (BF,),BL (L = CO. PF,, PCI,, PH,, ASH,, and SMe,). Related complexes have been made from SiCI, or SiF, and diboron tetrahalides in the presence of CO or PF, , and the compounds (SiCI,),(BClz)BCO and (SiC13)a(BF2)BPF3 have been characterised.
The molecular structure of perfluorodisiloxane (SiF&O has been determined by the sectormicrophotometer method of electron diffraction. The Si-F bond length is 1.554f0.010 A, the Si-0 bond length is 1.580f0.025 A, the Si-0-Si angle is 155.7f2.0" and the F-Si-F angle is 108.8f0.5". The relatively large uncertainties in these values arise from the closeness of the values of the Si-0 and Si-F distances (and hence the F.. . (Si). . . F and F . . . (Si). . . 0 distances); the Si-0 and Si-F bond distances are strongly correlated. The relative conformation of the trifluorosilyl groups has been studied in detail ; the angle of twist refines to a value of 34.6 f 1 So.Electron diffraction determinations have found angles at oxygen of 144+ 1" in disiloxane,l (H3S&0, and 121 +_ 1" in silyl methyl ether,2 H3SiOCH3. Since the Si-0-Si deformation frequency is believed to be very low, the angle in disiloxane (and possibly also in silyl methyl ether) must be increased by an uncertain correction to allow for '' shrinkage ". 3 The small stereochemical effect of the oxygen '' lone pairs " in these compounds has been interpreted in terms of the delocalization of these electrons into the vacant silicon 3d orbitals. The replacement of the hydrogen atoms in disiloxane by electron withdrawing fluorine atoms might be expected to enhance this effect, widening the angle at oxygen and shortening the Si-0 bond. Accordingly, we have carried out an electron diffraction study of perfluorodisiioxane in the vapour phase.
EXPERIMENTAL(SiCl3)20 was prepared by the partial hydrolysis of silicon tetrachloride ; water was added dropwise to a well-stirred solution of silicon tetrachloride in diethyl ether at -78°C (H,O : SiC14 : Et20 = 1 : 4 : 4), the volatiles were distilled off, and the fraction boiling at 130-135" was further purified by fractional condensation in the vacuum system. The (SiCI&O was distilled slowly through a tube packed with antimony trifluoride to which a little antimony pentachloride catalyst had been added,6 and the (SiF,),O product purified by repeated fractional condensation. The infra-red spectrum indicated a trace of an Si-Cl derivative, which could not be removed by further purification, but was otherwise consistent with pure (SiF&O. The molecular weight in the vapour phase was found to be 187 (calc.for (SiF3)20 ; 186.2).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.