On the Temperature Dependence of Lanthanide-Induced NMR Shifts.
Abstract
The current theories of the origin of lanthanide-induced NMR shifts are examined and compared with one another and with experimental results in an attempt to understand the temperature dependence of the shifts. It is concluded that shifts arising from a pseudocontact mechanism should in general show a 1/T squared behavior as predicted by Bleaney. In most situations with a fixed molecular geometry, theory does not predict a substantial 1/T component of the shift; but in some instances a fortuitous combination of crystal field parameters can lead to additional 1/T to the n power components (n greater than or equal to 3) which cause the overall shift to appear to be a linear function of 1/T with a large intercept at 1/T = 0. Extension of Bleaney's method to the (positive) 1/T cubed term shows it to be negligible compared to that in 1/T squared for systems with J = 3/2 and relatively small (approximately 10%) for larger J. In the absence of detailed experimental studies of crystal field parameters in solution, it is likely that for the majority of lanthanide adduct systems the most realistic description of the proton shifts is in terms of the well-established 1/T squared dependence.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 11, 1976
- Accession Number
- ADA023232
Entities
People
- E. W. Stout Jr.
- Herbert S. Gutowsky
Organizations
- University of Illinois Urbana–Champaign