Carol Creutz of Stanford University are thanked for some of the compounds used in this research

The hyperfine structure in the ESR of the 5+ ion has confirmed the equivalence of the two cobalt atoms. The next important piece of information about these dimers that was obtained was the actual disposition of the four atomic Co02Co units in the 5+ cation. Following this, Schaeffer(ll) determined the structure of the diamagnetic 4+ salt and found the 0-0 distance to be 1.

In 1961 Haim and Wilmarth(l2) were the first to isolate the decacyano analogues of the peroxo- and superoxo-decaamines. This choice leads to an internally consistent formulation of the tasks for all the spectrums. In the decaamine there is a very weak but definite tail on the red side of the low energy M - L charge.

In addition to the internal consistency of the calculated Dq, Dt, and B, there is other experimental evidence for the assignment. This instability has led various authors to include decacyanide peaks in the spectrum, which we believe are spurious. To classify the spectrum of decacyanide, we looked at it at different pHs.

Perhaps the most important result of our ligand field analysis of the peroxo and superoxo spectra is the positioning of 02 - close to NH3 in the spectrochemical series.

ELECTRONIC STRUCTURAL STUDIES OF PYRAZINE BRIDGED RUTHENIUM DIMERS

After the appearance in the literature of the ruthenium pyrazine dimer, a second case of a near-IR transition in a stable mixed valent dimer was reported. With all this in mind, we set out to investigate the electronic structure of the ruthenium dimers, especially the 5+ ion. The field was calibrated using a standard sample of solid diphenylpicrylhydrazine (K and K Chemical Comp.) placed in the rear compartment of the double-cavity assembly.

No measurements were taken at lower temperatures because the age of the thermocouple prevented accurate measurements at these lower temperatures. The diamagnetism of the nylon sample holder was corrected using diamagnetic measurements obtained on the holder alone. Based on the curves in Figure II-1, a description of the 5+ species as anionic pyrazine bridging two Ru(III) ions is untenable.

It may indicate the roughness of the calculation itself, as it neglects the spin-spin interaction. The most interesting feature of the ill-II ion spectrum, as mentioned earlier, is the unusually intense near-IR band, a band attributed by Taube(43) to Ru(III)Ru(II) - Ru(II)Ru(III) electron transfer. Since it is absent in the II-II· and ill-III salts, it could be argued that it arises from the mixed valence nature of the 5+ cation.

No sign of the II-II ion is present in the final solution as would be expected from a disproportionation mechanism.·. For example, by examining the ESR signal of the III-II compound over a long period, one sees a marked change in signal position and shape. A sample of the 5+ ion supposedly analyzed at Stanford was examined using Weissenberg X-ray techniques immediately after arriving here.

It was not possible to determine the exact group due to external reflections arising from imperfections in the crystal. This could be due to an additional large increase in the rate of tunnel construction due to the smaller barrier in Figure II.8, or to some kind of 'photocatalyzed' mechanism that is as yet poorly understood. The cleavage of the b3u (xz + xz) and b2g(xz - xz) levels is due to their interaction with the b2g(7Tb) and b3u (7T*) pyrazine levels.

The presence of only one kind of ruthenium atom in the ESCA experiments, as well as a single NH3 stretch in the IR experiments, can now be explained in terms of the postulated Ru(IIi)-Ru(IIi) ground state. This indicates that ligand reorganization is not extensive after "transfer" (excitation) of the electron.

THE CRYSTAL, MOLECULAR, AND ELECTRONIC STRUCTURE OF

Attempts have already been made to determine the structure of the ruthenium monomer (?6), but due to disorder in the crystal it was not possible to obtain exact bond lengths. In addition to the question of the RuNNRu angle, the question of the N-N length in the dimer was important. Of the 3040 independent reflections, 2645 were calculated to be greater than zero and were used in structure refinement.

The linear structure of the RuN2Ru unit is consistent with the infrared results, which show only a very weak band in the cm - i region. This reduced Ru-N2 distance in the monomer, when compared to the dimer, would be consistent with a larger positive charge on the metal of the monomer. Currently, instruments have been designed that will maintain temperature control in the Cary sample cells within the required degree of accuracy.

3h intermediate of M(C0)5 • We present the study of the vapor phase flash photolysis of the hexacarbonyls. We suggest that an investigation of the emission of the µ-nitrogen and µ-pyrazinedecamamine diruthenium dimers (as well as their monomers) be undertaken. Going to the 5+ dimer, it may be possible for spin-excited luminescence to appear in the infrared region of the spectrum, corresponding to the near-IR absorption at 1600 nm.

We believe that both series of connections should be further investigated to verify the nature of the coupling mechanism(s) present. In order to find out whether differences exist in the coupling mechanism, it is suggested that a low-temperature ESR study of the VO 2+. An attempt should also be made to observe a contact shift of the ligand aromatic protons in the NMR.

If superexchange is operative, unpaired spin density will be present in the ls H orbitals of the rings and a large paramagnetic shift will be observed. Much effort has gone into explaining the nature of the interactions that cause this phenomenon. The second method of data processing that should be used is a refinement of the first.

These three treatments should provide a relatively consistent value for the magnitude of barriers in biferrocene. An understanding of the bonding in the ruthenium-nitrogen dimer has also been hampered by the lack of comparable nitrogen bridge forms.