ELECTRONIC STRUCTURE OF TRIS(ALPHA,ALPHA'-DIPYRIDYL)IRON(2) ION

The π-electron structure of the tris(α,α’-dipyridyl)iron(II) ion was theoretically studied by the method of composite system, with the results successful in explaining the observed peak positions and intensities of the electronic absorption spectrum. According to the results, the bands at ˜20,000 and 33,600 cm-1 were assigned, respectively, to the charge-transfer transition from the metal to the lowest vacant MO of the ligand and to the π-π* transition within the ligand π-electron system. The other two bands at ˜29,000 and ˜40,000 cm-1 with several shoulders were assigned to the charge-transfer transition to the second lowest vacant MO and to the third charge-transfer transition mixing with the second π-π* transition in the ligand, respectively. The ground state was calculated to be stabilized by 0.86 eV by the charge-transfer interaction of electrons between the metal ion and the ligand. This can explain the remarkable stability of the complex ion. The nature of the excited states was also discussed in detail, with the result that the transferred electron is delocalized on the whole ligand π-electron system, in contrast with the current view that the character of the charge-transfer transition is predominantly determined by the α-diimine skeleton. © 1969, American Chemical Society. All rights reserved.