C. H. Holm

NMR Study of Ferrocene, Ruthenocene, and Titanocene Dichloride

The line widths of the proton magnetic resonance absorption spectra and the spin‐lattice relaxation times for polycrystalline samples of ferrocene, ruthenocene, and titanocene dichloride were measured as functions of temperature, and are interpreted in terms of reorientation of the cyclopentadienyl rings about their fivefold axes. At low temperatures such reorientation is interpretable in terms of an activated process governed by a single correlation time, and the barrier restricting reorientation is obtained. At higher temperatures for these substances, as well as for benzene, such an interpretation is not suitable, and a hypothesis involving the coupling and uncoupling of adjacent rings taking part in reorientation is proposed to account for the data.

Electronic Structure of Sodium‐Ammonia Solutions by Nuclear Magnetic Resonance

Knight shifts (ΔH) of the N14 and Na23 nuclear magnetic resonances have been observed in liquid sodium‐ammonia solutions at 7000 gauss as a function of the mole ratio R=(moles NH3)/(moles Na) for 10⪝R ⪝1000. The Knight shifts decrease with increasing R and for R≈10, ΔH(N14)≈4, ΔH(Na23)≈1 gauss. The experimental results in these variable composition solutions are conveniently discussed in terms of P(N14) and P(Na23), the average hyperfine contact densities of N14 and Na23 nuclei at an unpaired electron. P(N14) and P(Na23) were estimated from K–NH3 paramagnetic susceptibility data and the ΔHs. For 50<R<400, P(Na23)=5–3×10—3 P0(Na23) where P0(Na23) is the contact density in an isolated sodium atom. In this concentration range we conclude the odd electrons move in highly expanded orbitals about Na+ ions similar to those appropriate to tetrahedrally bonded P+ ions in P‐doped silicon where a similar reduction in the contact hyperfine density is found. Marked electron condensation on Na+ ions occurs at R⪝50 whe...