A convenient new method is developed for the preparation of 1‘,1‘‘‘-disubstituted biferrocenes which can be oxidized with iodine to a new series of mixed-valence compounds. The X-ray structures of 1‘,1‘‘‘-dimethoxymethyl, 1‘,1‘‘‘-diethoxyl, 1‘,1‘‘‘-dimethyl, 1‘,1‘‘‘-dihydroxymethyl, 1‘,1‘‘‘-dibenzoyloxymethyl, 1‘,1‘‘‘-dimethylthio, and 1‘,1‘‘‘-diethylthio neutral biferrocenes and the mixed-valence 1‘,1‘‘‘-diethoxyl, 1‘,1‘‘‘-dimethyl, 1‘,1‘‘‘-dibenzoyloxymethyl, and 1‘,1‘‘‘-diphenylthio biferrocenium triiodide salts have been determined at 298 K. The rates of intramolecular electron transfer in these mixed-valence cations were estimated by variable-temperature 57Fe Mössbauer experiment.

The results of an X-ray structure determination of 1 ',3',1 "',3"'-tetraethylbiferrocenium triiodide, the effects of changing the relative positions of ethyl substituents from 1 ',3',1 "',3"' t o 1 ',2'"''',2'" o n the intramolecular electron-transfer rates of biferrocenium salts in the solid state, and a theoretical explanation of the influence of steric factors o n the electron-transfer rates are reported.

Relatively minor perturbations caused by Cp ring substituents in a series of mixed-valence biferrocenium cations have pronounced effects on the electronic structure and rate of intramolecular electron transfer. The X-ray structures of 1‘,2‘,1‘‘‘,2‘‘‘-tetrapropylbiferrocene, 1‘,2‘,1‘‘‘,2‘‘‘-tetrabenzylbiferrocene, 1‘,3‘,1‘‘‘,3‘‘‘-tetrapropylbiferrocene, 1‘,3‘,1‘‘‘,3‘‘‘-tetrabenzylbiferrocene, and their corresponding mixed-valence biferrocenium triiodide salts have been determined at 298 K. The rates of intramolecular electron transfer in the mixed-valence cations were estimated by variable-temperature 57Fe Mössbauer spectroscopy (time scale ∼107 s-1). The features in all of the 80 K spectra include two doublets, one with a quadrupole splitting (ΔE Q) of ∼2 mm s-1 (Fe(II) site) and the other with ΔE Q = ∼0.6 mm s-1 (Fe(III) site). This pattern of two doublets is expected for a mixed-valence biferrocenium cation which is valence-trapped on the time scale of the Mössbauer experiment (electron-transfer rate < ∼107 s-1 in the solid state). Increasing the sample temperature in 1‘,2‘,1‘‘‘,2‘‘‘-tetrapropylbiferrocenium triiodide, 1‘,2‘,1‘‘‘,2‘‘‘-tetrabenzylbiferrocenium triiodide, and 1‘,3‘,1‘‘‘,3‘‘‘-tetrabenzylbiferrocenium triiodide causes the two doublets to move together with no discernible line broadening, eventually becoming a single “average-valence” doublet at temperatures of 295, 265, and 190 K, respectively. In the case of 1‘,3‘,1‘‘‘,3‘‘‘-tetrapropylbiferrocenium triiodide, the two doublets at low temperatures do not coalesce into an average-valence doublet at 300 K (electron-transfer rate < ∼10 s-1 at 300 K). Thus, the micromodification of the relative positions of the alkyl substituents and the nature of the alkyl substituents has a dramatic influence on the rate of intramolecular electron transfer. The deviations of the Cp rings from the parallel position correlate quite well with the Mössbauer critical temperature for electronic delocalization−localization in mixed-valence cations. Qualitatively, we suggest that the metal nonbonding orbitals (d x 2 - y 2 , d xy ) start to interact with the ligand π orbitals as the Cp rings tilt from the parallel position. On the basis of the density functional calculations, a theoretical explanation of the influence of bending back the Cp rings on the electron-transfer rates is presented. The electrochemical measurements, IR data, and near-IR spectra for these mixed-valence biferrocenium cations are also presented.

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Two series of novel biferrocenes containing crown ethers have been prepared. The new compounds include 1‘,1‘ ‘‘-bis(1,4,7,10,13-pentaoxa-16-azacyclooctadecane-16-methyl)biferrocene (7) and 1‘,1‘ ‘‘-bis(1,4,7,10-tetraoxa-13-azacyclopentadecane-13-methyl)biferrocene (8). The complexing behavior toward alkali and alkaline earth metal cations for 7 and 8 was investigated. Solid-state structures have been determined for NaPF6 and KPF6 complexes of 8. The reaction products of 7 and 1-(1,4,7,10,13-pentaoxa-16-azacyclooctadecane-16-methyl)ferrocene with I2 have also been characterized by structural determinations, 1H NMR, magnetic measurements, and 57Fe Mössbauer technique. Complexation properties for 7 and 8 have been assessed by use of 1H NMR, cyclic voltammetry measurements, and 57Fe Mössbauer analyses. When the system was studied by cyclic voltammetry, new redox couples were observed in the presence of certain alkaline earth metal cations. For example, the electrochemical behavior observed for 8 with Ba2+ ion is fundamentally different since two new redox couples are observed for Ba2+ concentrations within the range 0 < [Ba2+] < 2equiv. The peak currents for the two new redox couples increase with the concentration of Ba2+ ion until a full equivalent is added; at this point, the original redox couples disappear and the new redox couples reach full development. This is quite unusual since compounds 7 and 8 do not have a well-formed cavity to facilitate the formation of internal metal cation complexes. Furthermore, the Mössbauer and UV/vis studies suggest no direct interaction between the iron atom and metal cation. The solid-state electron transfer in mixed-valence 1‘,1‘ ‘‘-bis(crown ether)biferrocenium cations was also characterized by Mössbauer spectroscopy. The features in all of the Mössbauer spectra include two doublets, one with a quadrupole splitting (ΔE Q) of ∼2.2 mms-1 (Fe(II) site) and the other with ΔE Q = ∼0.4 mms-1 (Fe(III) site). The Mössbauer studies indicate that the electron-transfer rates in the series of mixed-valence 1‘,1‘ ‘‘-bis(crown ether)biferrocenium cations are less than 107 s-1 in the solid state.

The results of X-Ray structural determinations, electrochemical measurements, near-IR, 57Fe Mossbauer measurements, and an explanation of the influence of steric factors o n the electron-transfer rates for a series of polyalkyl substituted mixed-valence biferrocenium triiodides are reported.

ORIGINAL RESEARCH ARTICLEwith minimum electrical resistivity (9). Optimization of the optical and electrical properties requires careful control of the fabrication processes. Sputtering with good reliability, high growth rate and better control of the film characteristics is one of the most often used methods for ITO film preparation (10). Tului et al (11) deposited ITO films onto glass substrates using magnetron sputtering under different atmospheres. They found that the presence of oxygen in the deposition chamber affected the growth direction of the crystal grains, which determined the conductivity of the ITO film. At high oxygen content, the films grew along the <111> direction, with high resistivity; at low oxygen content, the grains grew also along other orientations -e.g., the <100> direction -and the resistivity was decreased. Kavei and Mohammadi Gheidari (12) deposited ITO films on a glass substrate using the sputtering system with different sputtering gas pressures at room temperature. They reported that the optimum sputtering gas pressure of 27 mTorr provided a homogenous and most favorable rate of deposition, leading to good combined electrical conductivity and optical transparency. Meng et al (13) deposited ITO films onto polycarbonate substrate at room temperature by the ion beam-assisted deposition technique at different screen voltages. They found that the film prepared at low screen voltage showed an amorphous structure with a high optical transmittance, while the film prepared at high screen voltage showed a polycrystalline structure with a high electrical resistivity.

A novel convenien t method for preparing unsymmetrical I, I '-dis ubstituted ferrocen yI phosphine ligands by using the readily accessible I,l'-dibromofcrrocenc as a precursor is described. The method is of interest for modifying the chelating Ierrocenyl phosphine ligands in view of the growing influence of homogeneous catalysis in organic synthesis, manipulation of materials and production of high optical yield.The use of ferrocenyl phosphincs as ligands in synthetic applications of the rhodium-, ruthcnmm-, and palladium-catalyzed hydrogenation of oletlns'" and nickel-and palladium-catalyzed Grignard cross-coupling reactions is well known.?" Recently, the chemical uniqueness and indus trial importance of the symmetrical metalloligand I, 1'-bis(diphenylphosphine)ferrocene 1 (dppt) synthesized more than two decades ago have been fully appreciated." In particular it has been found that cationic Ril(I) complexes of 1 are efficient hydrogenation catalysts for olefin reduction.'