Ferrocene electronic structure

Fig. 2. Electronic structure of biferrocene (2) (a) energy diagram (b) illustration of large electronic interaction between dx2 >2 orbitals (e2 ) of ferrocene units through pz orbitals of Cp rings (54).

Next let us examine a QM/MM model system of complex 3 where the steric influence of the phenyl substituents and of the ferrocene is accounted for but the electronic effects have been largely eliminated (model B). In other words, the peripheral groups have been delegated to the MM region, while keeping the molecular system used for electronic structure calculation identical to that in model A. 

This problem will be considered on the basis of charge-transfer coordination of organic polynitriles to substituted ferrocenes. The practical significance of the charge-transfer coordinative species (salts) is their ferromagnetic behavior (see Section 8.5). The salts contain the cation-radical and anion-radical counterparts. Peculiarities in electronic structures of the cation-radical parts within the salts are topics of our interest. 

The nature and extent of /-orbital participation in the bonding of uranocene and other bis(cyclooctatetraenyl) actinides has never been satisfactorily established, although a good deal of effort has been expended on it. The X-ray structures do not resolve the issue because an ionically bonded model would also lead to a sandwich-type structure (for example, MgCp2 has essentially the same structure as ferrocene). Other physical techniques have been used, but the complexity of the electronic structures often leads to ambiguous interpretations. 

A first group of compounds Ce Cg2, Gd Cg2, Y Cg2, and the major [C2v] and minor [Cs] isomers of La Cg2 and Pr Cg2 showed two oxidation steps, the first reversible and the second irreversible, even at scan rates up to 1 V/s. The low potential of the first oxidation step, close to that of the ferrocene/ferrocenium couple (see Table 8.3 and Fig. 8.4), made these compounds rather good electron donors. These compounds could also be reduced in four to six distinct steps, most of them reversible, and their reducing ability was found even higher than that of and similar to that of the major isomer of Cg2 (C2). Noticeably, all these compounds had a very low electrochemical HOMO-LUMO gap (A ,gap<0.50 V). In addition, similar UV/Visible spectra were obtained for all of them,28 suggesting also similar electronic structures. ESR showed that Y Cg229 and both isomers of La CX249 52 are radical species and consequently that the formal oxidation state of the metal in these structures is probably + 3. Therefore, their low HOMO-LUMO gap is probably a consequence of their open-shell electronic structure. 

A Resonating-Bond Treatment of Ferrocene.—The electronic structure of ferrocene has been treated by many investigators.124 We shall discuss it in terms of resonating covalent bonds.125... 

The principal innovations that have been made in the discussion of the theory of the chemical bond in this edition are the wide application of the electroneutrality principle and the use of an empirical equation (Sec. 7-10) for the evaluation of the bond numbers of fractional bonds from the observed bond lengths. A new theory of the structure of electron-deficient substances, the resonating-valence-bond theory, is described and used in the discussion of the boranes, ferrocene, and other substances. A detailed discussion of the valence-bond theory of the electronic structure of metals and intermetallic compounds is also presented. 

A rather similar situation regarding the breakdown of Koopmans theorem exists for the metallocenes. The electronic structures of these interesting compounds have attracted the attention of both theoreticians and experimentalists for several years. Ferrocene is the metallocene that has been studied the most extensively. From the UPS standpoint this stems from the diamagnetism of the neutral molecule and the stability of the ferricenium cation. 

While dicyclopentadienyl compounds of transition metals (see Transition Metals) typically have a ferrocene-hke (see Ferrocene) sandwich structure, the electron-deficient cyclopentadienides of the main group metals tend to form polymers with bridging cyclopentadienyl (Cp) groups. Although exceptions are known, the tendency is rather consistent. The element zinc, owing to its borderline position between transition metals and main group metals, presents a variety of coordination (see Coordination Numbers Geometries) modes with the Cp anion. 

The reaction of 1,3-diboroles 4, LiMe and [ (C5Me5)RuCl 4] leads to the violet, highly air-sensitive Ru sandwich complexes 1810. The compounds 17 and 18 are derived from ferrocene and ruthenocene by formal replacement of two CH groups for B-R units. Therefore the complexes should have only 16 valence electrons (VE). However, the electronic structure of the iron compound 17, studied by EH-MO theory, exhibits a unique bonding The electron density of two B-C c orbitals participates in the bonding by... 

The reaction of iron(ll) chloride with [K(THF)(P2C3/-Bu3)] produced the orange ferrocene 120 <2001JCD1013>. The molecular and electronic structure of the complex was studied by photoelectron spectroscopy and DFT. 

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