Seminars Archive
Emiliano Fonda
Abstract
Tuesday, June 27, 2000, 14:30
Seminar Room, ground floor, Building "T"
Sincrotrone Trieste, Basovizza
I.D. required for external visitors
EXAFS data analysis of vitamin B12 models complexes: a methodological concern
Emiliano Fonda
(Universit di Trieste)
ABSTRACT
Several EXAFS studies have been carried out on the vitamin B12
system (M. D. Wirt et al. JACS, (1991) 113, 5299),and its models (M. Giorgietti
et al., Organometallics (1996) 15, 3491). Sometimes controversial (if not
erroneous) results were obtained as compared with crystallographic results
(C. Kratky et al., JACS, (1995) 17, 4654, L. Randaccio and S. Geremia,
Organometallics, (1997) 16, 4951). In order to contribute to clarify these
important aspects, we highlight some intrinsic limits in the EXAFS Fourier
-filtering analysis and suggest a way to overcome these limits and to move
towards a more reliable analysis. First we show that the classical analysis
technique should be discarded, since it leads (often) to trivial errors.
Then, we propose a more complex but flexible method, that takes advantage
of the new generation of multiple scattering EXAFS analysis software (we
employed UWXAFS/FEFF7.0). This method mostly exploits the available information
on the systems during the parameter refinement and it optimally works for
coordination compounds containing chelate ligands. We rate an accuracy
in co-ordination distances of about 0.05. However, this
method alone it is not capable to give the "good result", but a cross check
using local minimum mapping technique is necessary.
