The low-frequency resonance Raman spectra of the electron donor-acceptor complexes of hexamethylbenzene-h,8 and -d18 with the acceptors TCNE and TCNQ, and the complexes of p-xylene-A10 and -dxo with TCNE, are reported. The previously observed Raman features of the hexamethylbenzene (HMB)/TCNE complex, assigned to the first and second overtones of the donor-acceptor stretch, are reinvestigated. The mode at about 220 cm"1 in HMB-A18/TCNE is observed to shift to 200 cm"1 in HMB-
determine, in many cases, the isotropic chemical shifts, nuclear quadrupole coupling constants, and electric field gradient tensor asymmetry parameters for each of the three main types of nonequivalent oxygen in alkaline earth metasilicates, for a total of nine pieces of information per silicate. These results are to be compared with the results of 29Si NMR experiments, which can yield at best only three pieces of information, the individual components of the chemical shielding tensor. When higher field (or single crystal) data become available, it should also be possible to determine the overall breadth of the chemical shielding interaction for 17G in silicates with some accuracy. Thus, nO NMR is likely to become a particularly powerful tool for investigating bonding in such systems. The results we have obtained to date show interesting correlations between isotropic chemical shift and cation radius, which may be useful in analyzing the structures Charge-Transfer Transitions of 2:1 Electron of less well characterized systems (e.g., glasses), in addition to showing a very strong correlation between bridging and nonbridging !70 e^-qQ/h values and between bridging and nonbridging ,70 e1 2qQ/h values and the alkaline earth metal electronegativities.Acknowledgment. We thank Drs. N. Janes, G. L. Turner, and C. T. G. Knight for many useful discussions. This work was supported in part by the United States National Science Foundation Solid-State Chemistry Program (Grant DMR 83-11339, H.K.C.T.), by the Geochemistry Program (Grant EAR 84-08421), by the Department of Energy (Grant DE-FG22-82PC60779), and by the Mobil Foundation (S.E.S.).
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