Comparison of crystal field dependent and independent methods to analyse lanthanide induced NMR shifts in axially symmetric complexes. Part II: systems with a C4 symmetry axis.
Analysis of the LIS data for several series of Ln(3+) complexes of C(4) symmetry in terms of structural changes, crystal-field effects and/or variation of hyperfine constants along the lanthanide series was undertaken using a combination of the two-nuclei and three-nuclei techniques together with the classical onenucleus technique. Isostructurality of whole series of complexes, with changes of the F(i), and B(0) (2) parameters, was clearly defined for the complexes of L by the combination of the two first methods. Small changes, involving the three F(i), G(i) and B(0) (2) parameters, are observed for the series of complexes of L-L4, using the three data plotting methods. Some of the plots according to the two- and three-nuclei methods are accidentally linear, without necessarily implying isostructurality of the complexes, as they involve parameters, which may be insensitive to any small structural changes occurring in these systems. These parameter variations could result from a magnification, by the present graphical analysis, of the breaks expected from the gradual structural changes along the series due to the lanthanide contraction. The alpha and beta parameters of the three-nuclei method are not diagnostic of the type of structures the complexes have in solution, due to their very indirect dependence on the geometric factors.
Geraldes
Carlos F G C
CF
Department of Biochemistry and Center of Neurosciences, University of Coimbra, P.O. Box 3126 Coimbra 3001-401, Portugal. geraldes@ci.uc.pt
Zhang
Shanrong
S
Sherry
A Dean
AD