The electronic structure of the chloroferrocenes

Abstract

We h~ve measured the ionization potentials of gaseous ferrocene and the symmetrically ~ub~tlt~ted chlor~fe?"ocenes, F~( CsHs _ NCI N h (O..;;N";;5) by electron impact techniques. The lOntzatlOn potentIal IS found to mcrease in direct proportion to the number of chlorine substit~tions. !hese results indicate that chlorine ring substitutions result in greater overlap of the 11"-nng orbItals and the metal d orbitals. The binding energies of the unoccupied orbitals of ferrocene and 1,I'-dichloroferrocene have been inferred from photoabsorption studies. The effect of symmetric dichlorination on the splitting of the unoccupied 5e l ferrocene molecular orbital is described. g

Comparison of the electronic structures of disubstituted ferrocenes

“…The assignment of the photoabsorption features to one-electron transitions depends crucially upon the assumed level ordering of the ferrocene molecular orbitals-a matter of considerable controversy (ref 2 and the references therein). There are advocates for an orbital ordering (in terms of increasing binding energy) alg(d) < e^d) < ß1 ( ) < elg(x).…”

“…This is in agreement with simple expectations for molecular orbital theory and optical absorption data. [12][13][14][15][16] If we assume that the B and C Racah electron repulsion parameters are related according to 4B = C,13 the difference of the electronic transitions energies is given by E(5elg(b)-8alg) -S(5elg(a)-8alg) = ( !2 + 12 + 420B2)1/2 (2) and the sum of the electronic transition energies £(5elg(b)-8alg) + £(5elg(a)-8alg) = 2 2 -, + 4B (3) The repulsion parameters are assumed to be unaltered as a result of the disubstitutions to ferrocene. The appropriate electronic transition energies if not measured and reported in Table I can be estimated from Table II.…”

“…There exist a considerable number of photoabsorption spectra for a variety of metallocenes, however, the assignment of the absorption features remains far from satisfactory. Even in the case of ferrocene,1 for which the assignment of absorption features is better established, there is considerable controversy as to the level ordering of some of the molecular orbitals and one-electron transitions (ref 2 and the references therein) as a result of the photoemission data. The existence of photoelectron spectra of ferrocene,3-9 , -dimethylferrocene,3,6 l,l'-dibromoferrocene,5 and , '-dichloroferrocene3 '5,6 together with photoabsorption data make the investigation of the effect of symmetric substitutions on the ferrocene molecular orbitals possible for both occupied and unoccupied orbitals, assuming one particular level ordering for ferrocene.…”

Preferential Bonding Orientations of Ferrocene on Surfaces

“…The spectra for ferrocene on Cu(100) are qualitatively similar to those obtained on the Ag(100) surface. Again, on the basis of theoretical calculations of the ground-state molecular orbitals of ferrocene [16][17][18][19][20][21][22] and gas-phase photoemission and ionization potential studies, [23][24][25][26][27] we can assign these photoemission features of the adsorbed species (Table 2, Figure 5). The ferrocene 8a 1g and 4e 2g molecular orbitals induce the 4.2 eV feature that overlaps with the Cu 3d bands.…”

“…There exists a strong similarity between the gas-phase photoemission spectra of ferrocene and condensed ferrocene, 5 although the molecule to substrate and intermolecular interactions have been observed to shift, split, or broaden the observed energies of the molecular orbitals. On the basis of theoretical calculations of the ground-state molecular orbitals of ferrocene [16][17][18][19][20][21][22] as well as gas-phase photoemission and ionization potential studies, [23][24][25][26][27] we can assign the adsorbed ferrocene-induced photoemission features to the molecular orbitals of ferrocene ( Table 2, Figures 2 and 3). The features at 5.4 and 4.1 eV arise from the ferrocene 8a 1g and 4e 2g Figure 2.…”