ESR Spectra of the Fluorinated Silyl Radicals

Abstract

Isotropic ESR spectra of · SiH2F, · SiHF2, and · SiF3 are reported. The radicals were produced by radiolysis of H3SiF, H2SiF2, and HSiF3 in an SF6 matrix. The hyperfine parameters in gauss are: for · SiH2F, aH=34.6, aF=55.2; for · SiHF2, aH=89.9, aF=77.8; and for · SiF3, aF=136.6, aSi=(−) 498.0. The large 29Si hyperfine constant for · SiF3 shows that the radical is strongly pyramidal, probably as a result of the high ionic character of the Si–F bonds. The proton hyperfine constants are believed to be positive and the parallel of · SiHF2 with · HPO2− (aH=82.5 G) is noted. The radical (CH3)2SiF · was also produced in liquid phase photolysis experiments and has the parameters aH=4.53 and aF=65.21 G.

An INDO study of the hyperfine coupling constants and equilibrium geometries of some tetra-atomic radicals

“…planarity found for SiFa is in agreement with the large ~gSi splitting of -498 G [7] and a prediction by Pauling [14] that the large electronegativity difference between silicon and fluorine should lead to bond angles smaller than expected for sp a hybridization t. The validity of our result for SiHa is less certain. The 29Si splitting of -190 G indicates a non-planar structure but our calculated bond angle of 110.9 ~ is substantially smaller than the value of 113-114 ~ deduced by Sharp and Symons [10].…”

“…E.S.R. data on the fluoromethyl radicals have been available for some time [1] but it is only in the last two years that coupling constants have been obtained for other series of this type including the chloromethyl radicals [2][3][4][5], the fiuorochloromethyl radicals [6], the fluorosilyl radicals [7], the methylchlorosilyl radicals [8,9], the trimethylsilylmethylsilyl radicals [6], and the methylsilyl radicals [10]. These series exhibit a trend towards more pyramidal structures as increasingly electronegative substituents are introduced.…”

“…Semi-empirical INDO molecular orbital calculations successfully accounted for variations in the geometry and hyperfine coupling constants of fluorinated methyl radicals [11] ; the recent extension of the INDO method to include second row elements [12] opens up the possibility of performing similar calculations on radicals containing silicon or chlorine. We now present the results of an investigation involving 13 tetra-atomic radicals containing C, Si, H, F and C1 including the fluorosilyl radicals which have unusually large proton coupling constants [7].…”

E.S.R. spectra of SiF3radicals produced in a single crystal of SiF4

“…spectra of SiF 3 Taylor & Francis makes every effort to ensure the accuracy of all the information (the "Content") contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content.…”

“…Recently, Merritt and Fessenden [3] reported an isotropic E.S.R. spectrum of SiF z radicals in an SF 6 matrix.…”