Ab initio G2 and DFT calculations on electron affinity of cyclopentadiene, silole, germole and their 2,3,4,5-tetraphenyl substituted analogs: structure, stability and EPR parameters of the radical anions
Energies, geometries and electronic structures of cyclopentadiene (1), silole (2), germole (3) and their radical anions (RAs) 1a–3a have been studied by quantum-chemical methods at the G2(MP2, SVP) and DFT B3LYP/6-31G(d,p) levels. According to G2(MP2, SVP) calculations 1–3 have negative electron affinities (EAs) equal to −1.09, −0.06 and −0.15 eV, respectively, and hence their RAs are unstable in the gas phase. 1,2,3,4-Tetraphenylcyclopenta-1,3-diene (4) and 2,3,4,5-tetraphenylsubstituted-2 (5) and 3 (6) and their radical anions (4a–6a) were studied at the B3LYP/6-31G(d)//AM1 level. Substitution of cyclodienes results in significant stabilization of RAs 4–6 because of the effective delocalization of an extra electron within phenyl groups, especially those in positions 2 and 5, so 4–6 all have a positive EA. Our best estimates give for 4, 5 and 6 EA values 0.98, 1.30 and 1.13 eV respectively. The calculated hyperfine coupling (hfc) constants a(H) for radical anions 4a–6a are in a good agreement with experimental values. Variation of group 14 element (C, Si, Ge) in the series 1–3 and 4–6 do not produce a monotonous change of EA and hfc values.