Assessing Alkyl-, Silyl-, and Halo-Substituent Effects on the Electron Affinities of Silyl Radicals

Neutral anion energy differences for a large class of α-substituted silyl radicals have been computed to determine
the effect of alkyl, silyl, and halo substituents on their electron affinities. In particular, we report theoretical
predictions of the adiabatic electron affinities (AEAs), vertical electron affinities (VEAs), and vertical
detachment energies (VDEs) for a series of methyl-, silyl-, and halo-substituted silyl radical compounds.
This work utilizes the carefully calibrated DZP++ basis set (Chatgilialoglu, C. Chem. Rev. 2002, 102, 231),
in conjunction with the pure BLYP and OLYP functionals, as well as with the hybrid B3LYP, BHLYP,
PBE1PBE, MPW1K, and O3LYP functionals. Bromine has the largest effect in stabilizing the anions, and
the BLYP/DZP++ AEA for SiBr3 is 3.29 eV. The other predicted electron affinities are for SiH3 (1.37 eV),
SiH2CH3 (1.09 eV), SiH2F (1.54 eV), SiH2Cl (1.94 eV), SiH2Br (2.05 eV), SiH2(SiH3) (1.77 eV), SiH(CH3)2
(0.92 eV), SiHF2 (1.86 eV), SiHCl2 (2.53 eV), SiHBr2 (2.67 eV), Si(CH3)3 (0.86 eV), SiF3 (2.66 eV), SiCl3
(3.21 eV), Si(SiH3)3 (2.25 eV), and SiFClBr (3.13 eV). For the five silyl radicals where experimental data are
available, the BLYP functional gives the most accurate determination of AEAs; the average absolute error is
0.041 eV, whereas the corresponding errors for the O3LYP, MPW1K, PBE1PBE, B3LYP, OLYP, and BHLYP
functionals are 0.058, 0.060, 0.063, 0.085, 0.115, and 0.153 eV, respectively.