ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
The 13C and 1H NMR spectra of vanodocene were measured in the temperature range 208–377 K and compared with theory. To this end, the 3d3 term scheme of vanodocene is evaluated by a Hamiltonian which involves the Coulomb repulsion of the d electrons, their interaction with the D5d -coordinated ligands, and spin-orbit coupling. The adjustable parameters are chosen to fit the experimental ESR data and the weak bands at the low-energy side of the absorption spectrum. The reduced NMR shifts T(ΔH/H) of 13C and 1H, as calculated from the fine structure of the electronic ground state, depend on the well-known spatial structure, the ESR parameters, and on the adjustable radial spin densities at the ligand nuclei. In both cases only a slight temperature dependence is to be expected due to the orbitally nondegenerate ground state. This is in contradiction with the observed temperature slope of the reduced carbon shift. Thus, two modifications of the original assumptions are discussed. In the first place, the ligand-centered dipolar contribution is investigated theoretically. Although this effect improves the fit of both sets of spectra, it seems probable that in addition the nuclear coordinates change about 1% within the observed temperature range. The radial spin densities of vanadocene, however, are independent of the details of the fit procedure, yielding u2F(C) =−0.124(3) A(ring)−3 and u2F(H) =+0.0982(2) A(ring)−3 for the carbons and protons, respectively.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.452184
Permalink
