The first representatives of the radical anions of silatranes XSi(OCH₂CH₂)₃N – organic derivatives of the pentacoordinate silicon atom (X = Ph, 1; p-NO₂PhO, 2a; m-NO₂PhO, 2b; o-NO₂PhO, 2c) – were obtained and characterized by EPR spectroscopy. The structure of 1⁻˙, 2a⁻˙, 2b⁻˙, and 2c⁻˙ in polar solvents (C-PCM and COSMO models) was studied at the UMP2 and UB3PW91 levels of theory. The variation of structural characteristics and pentacoordinate character of the silicon atom in 1, 2 upon the attachment of an additional electron to them is discussed. The experimental hyperfine coupling constants a_N, a_H and those calculated with the UTPSSh/IGLOIII and UB3LYP/N07D methods using the UB3PW91 geometry (taking into account an effect of the potassium cation in the case of 1⁻˙) are in good mutual agreement.