Fluorides of Beryllium, Boron, and Carbon

The average values of the nearly constant intramolecular F—F distances for a given central atom A give interligand radii for fluorine of 128(2) pm in BeF molecules, 113(1) pm in BF molecules, and 108(1) pm in CF molecules (Table 1). The value of the ligand radius for fluorine bonded to carbon agrees with the Bartell radius because he obtained this from molecules in which the central atom is carbon. The radii of the anion-like fluorine ligand are not equal to the radius of 

Notes For more extensive tables and references for sttucnires see ref, 10. Calculaled structure. 

3-coordinated are consistently shorter than the bonds in 4-coordinated molecules and the bond length ratios BeF /BeFj, BeF /BF3, and CF4/CF3 have the values 

We expect therefore that chlorofluoro molecules of boron and carbon will also be close packed with F—Cl distances of 113 + 151 = 264 pm for boron molecules and of 113 + 144 = 257 pm for carbon molecules. In F2BCI, for example, the observed bond lengths are BF 131.5(6) pm and BCl 172.8(9) pm, with FBF 118.1(5)° [13], giving experimental F—F and F—Cl distances of 226(2) pm and 266(2) pm, respectively. In CF3CI [14], CF2CI2 [75], and CFCI3 [16] the F—Cl distances are 254,253, and 253 pm, respectively, in reasonable agreement with the predicted value of 257 pm. 

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