Sandwich-Type Mixed Tetrapyrrole Rare-Earth Triple-Decker Compounds. Effect of the Coordination Geometry on the Single-Molecule-Magnet Nature

Employment
of the raise-by-one step method starting from M­(TClPP)­(acac)
(acac = monoanion of acetylacetone) and [Pc­(OPh)8]­M′[Pc­(OPh)8] led to the isolation and free modulation of the two
rare-earth ions in the series of four mixed tetrapyrrole dysprosium
sandwich complexes {(TClPP)­M­[Pc­(OPh)8]­M′[Pc­(OPh)8]} [1–4; TClPP = dianion
of meso-tetrakis­(4-chlorophenyl)­porphyrin; Pc­(OPh)8 = dianion of 2,3,9,10,16,17,23,24-octa­(phenoxyl)­phthalocyanine;
M–M′ = Dy–Dy,
Y–Dy, Dy–Y, and Y–Y]. Single-crystal
X-ray diffraction analysis reveals different octacoordination geometries
for the two metal ions in terms of the twist angle (defined as the
rotation angle of one coordination square away from the eclipsed conformation
with the other) between the two neighboring tetrapyrrole rings for
the three dysprosium-containing isostructural triple-decker compounds,
with the metal ion locating between an inner phthalocyanine ligand
and an outer porphyrin ligand with a twist angle of 9.64–9.90°
and the one between two phthalocyanine ligands of 25.12–25.30°.
Systematic and comparative studies over the magnetic properties
reveal magnetic-field-induced single-molecule magnet (SMM), SMM, and
non-SMM nature for 1–3, respectively,
indicating the dominant effect of the coordination geometry of the
spin carrier, instead of the f–f interaction, on the magnetic
properties. The present result will be helpful for the future design
and synthesis of tetrapyrrole lanthanide SMMs with sandwich molecular
structures.