Ferrocene-Decorated (Phthalocyaninato)(Porphyrinato) Double- and Triple-Decker Rare Earth Complexes: Synthesis, Structure, and Electrochemical Properties

A series of four mixed (phthalocyaninato)­(porphyrinato)
rare earth
double-decker complexes (Pc)­M­[Por­(Fc)2] [Pc = phthalocyaninate; Por­(Fc)2 =
5,15-di­(ferrocenyl)-porphyrinate; M = Eu (1), Y (2), Ho (3), Lu (4)] and their europium­(III)
triple-decker counterpart (Pc)­Eu­(Pc)­Eu­[Por­(Fc)2] (5), each with two ferrocenyl
units at the meso-positions of their porphyrin ligands,
have been designed and prepared. The double- and triple-decker complexes 1–5 were characterized by elemental analysis
and various spectroscopic methods. The molecular structures of two
double-deckers 1 and 4 were also determined
by single-crystal X-ray diffraction analysis. Electrochemical studies
of these novel sandwich complexes revealed two consecutive ferrocene-based
one-electron oxidation waves, suggesting the effective electronic
coupling between the two ferrocenyl units. Nevertheless, the separation
between the two consecutive ferrocene-based oxidation waves increases
from 1 to 4, along with the decrease of
rare earth ionic radius, indicating the effect of rare earth size
on tuning the coupling between the two ferrocenyl units. Furthermore,
the splitting between the two ferrocene-based one-electron oxidations
for triple-decker 5 is even smaller than that for 1, showing that the electronic interaction between the two
ferrocene centers can also be tuned through changing the linking sandwich
framework from double-decker to triple-decker. For further understanding
of the electronic coupling between ferrocenyl groups, DFT calculation
is carried out to clarify the electronic delocalization and the molecular
orbital distribution in these double-decker complexes.