Binuclear complexes, electron

A special representative of class IIIA is the Creutz-Taube complex [101]. This is a binuclear complex [(NHjlsRufpyrazinelRufNHj) ]. Various experimental results led to conflicting conclusions concerning its electronic structure. A combined attack [101] has shown, however, that we are not dealing with a... 

The one-step reaction of H2prCl6] with MeC02Li under 02 in a mixed solvent of acetic acid and acetic anhydride yields the Ir11 binuclear complex [Ir2(/u-02CMe)2Cl2(C0)2].483 Crystal-structure determinations of [Ir2(/x-02CMe)2Cl2(C0)2L2], (295), where L = MeCN, DMSO, and py, are reported. The one-electron oxidation product for (295), L = py, is EPR active at 77 K the odd electron occupies the 6Ir Ir orbital. 

The dark red Ir11 binuclear complex [Ir(CO)(P(/i-tolyl)3)(mnt)]2, formed via one-electron oxidation of [Ir(CO)(P(/ -tolyl)3(mnt)] by ferrocenium, contains chelating mnt ligands bridging the Ir—Ir bond.639 The X-ray crystal structure shows square-pyramidal geometry at each Ir, and an Ir—Ir bond length of 2.706(2) A. 

In compliance with the nuclearity principle, polynuclear clusters are subdivided into a number of other subgroups, e.g. hexanuclear, octanuclear, etc. The binuclear clusters of technetium may be classified according to the electronic structure of their Tc-Tc2 bonds. Then, the d4-d4 complexes with quadruple M-M bonds are the father of all binuclear complexes with Tc-Tc bonds. The addition or removal of electrons from Tc-Tc bonds [1,11] should result in a decrease in the formal multiplicity of M-M bonds. Thus, for instance, the formal multiplicity of Tc-Tc bonds of d3-d3 and d5-d5 binuclear complexes equals3 3, that of d4 d5 and d4-d3 complexes equals 3.5, etc. 

Literature data are available on the electronic structures of two more binuclear technetium complexes [(NHjLlOHLTcf/i-O TcfOH NHj ] (a hypothetical complex with the structure and composition analogous to those of the ethylen-diamminetetra-acetate complex [54,55]) and Tc2(CO)10 (a binuclear complex with strong crystal field ligands [168,169]. We shall consider the results of these calculations in greater detail. 

In this regard it would be interesting to consider the electronic structure of some binuclear complexes of other elements. For example, an analogous effect of the bridging ligands on the reverse energy order of <5M-M and <5g M MO s was... 

Electron-Transfer in Simple Binuclear Complexes. In trying to understand the electron transfer mediation effects of peptide bonds and amino acid side chains on rates of electron transfer in simple systems that are amenable to detailed investigation, we have designed and synthesized a series of complexes which contain within a single molecule two different oxidizing agents —both of which are inert to substitution. The series of complexes we have synthesized is represented schematically by the general structure 1. 

The outer-sphere pathway k ) produces the final products directly, as shown by a rapid increase in absorbance at 474 nm, which is a maximum for Ru(NH3)5pz. At the same time, a rapid inner-sphere (A ,) production of the binuclear complex takes place. A slower absorbance increase at 474 nm arises from the back electron transfer in the binuclear intermediate This produces the original reactants which then undergo outer-sphere reaction (Atj). 

The binuclear unit also confers characteristic physical and spectroscopic properties to the complexes. Electronic spectra reveal a strong (e - 3000-4000 M-icm l) absorption band at 3(X)-400 nm with a characteristic low energy shoulder, both associated with the presence of an 0x0 bridge weaker (e 300-600 M lcm" ) features in the 400-550 nm region associated with the (p,-oxo)bis(p.-carboxylato)-diiron(in) core and d-d bands in the near IR region (Hgure 2a) (5,10). Laser excitation into the visible and near UV bands results in the observation of enhanced Raman features due to Fe-O-Fe vibrations (5,11) (see Chapter 3 for a more detailed discussion into the Raman spectra of these complexes). 

Consider a binuclear complex with metals A and B and assume that each metal contains one unpaired electron allocated to orbitals a and b, respectively (see Figure 6). Let us assume further that the states la> and lb> contain the contributions of the ligands (including the bridging ligands) and that we have orthogonalized the two functions, = 0. If only those two "active electrons are taken into account the electrostatic part of the Hamiltonian is... 

A large number of binuclear complexes of copper have been reported in the literature. As first noted by Patterson and Hohn [95], these systems may exhibit either two one-electron steps or a single two-electron... 

In a few instances, binuclear complexes have been reported in which the two copper atoms interact directly through a metal-metal bond. Two examples of such complexes are illustrated below [192, 193]. CV s run on the compound at left in both tetrahydrofuran and CH2CI2 indicated the presence of two separate electron-transfer steps that were quasi-reversible. 

Bi- and tetranuclear, three-center two-electron gold(I) complexes have been prepared containing polyfluorophenyl groups (129). The binuclear complexes are of the type discussed previously, [Ar(AuL)2]X and [Ar Au2(dpe) ]BF4, whereas the diarylaurates reacted to give tetranuclear compounds [Eq. (35)] suggested to be of the same type as the mixed metal complexes discussed above. 

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