Intramolecular dynamics of asymmetric lanthanide(III) porphyrin sandwich complexes in solution

Temperature dependencies of the H-1 NMR spectra of asymmetric double-decker complexes of DyH(oep)(tpp) (I) and LuH(oep)(tpp) (II), where tpp is tetrap henylporphyrin and oep is octaethylporphyrin, have been analyzed. The kinet ic and thermodynamic parameters for intramolecular phenyl ring rotations ha ve been determined. The rotation in (I) is characterized by k(298 K) = 11.4 s(-1), DeltaH(double dagger): = 48.0+/-6.0 kJ mol(-1) while in (II) the de rived parameters are found to bek(298K) = 14.0 s(-1) DeltaH(double dagger) = 65.5+/-7.1 kJ mol(-1). The possible reasons for the different characteris tics of these complexes are discussed. The structural parameters calculated for I and YbH(oep)(tpp) (III), indicate close similarities between the com plexes. Nevertheless, it appears that the principal values of the molar par amagnetic susceptibility tensor (Xi) differ significantly in these complexe s.