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), silo le (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) le vels. According to G2(MP2, SVP) calculations 1-3 have negative electron aff inities (EAs) equal to -1.09, -0.06 and -0.15 eV, respectively, and hence t heir RAs are unstable in the gas phase. 1,2,3,4-Tetraphenylcyclopenta-1,3-d iene (4) and 2,3,4,5-tetraphenylsubstituted-2 (5) and 3 (6) and their radic al anions (4a-6a) were studied at the B3LYP/6-31G(d)//AM1 level. Substituti on of cyclodienes results in significant stabilization of RAs 4-6 because o f the effective delocalization of an extra electron within phenyl groups, e specially those in positions 2 and 5, so 4-6 all have a positive EA. Our be st estimates give for 4, 5 and 6 EA values 0.98, 1.30 and 1.13 eV respectiv ely. The calculated hyperfine coupling (hfc) constants a(H) for radical ani ons 4a-6a are in a good agreement with experimental values. Variation of gr oup 14 element (C, Si, Ge) in the series 1-3 and 4-6 do not produce a monot onous change of EA and hfc values.