Enantiopure Benzamidinate/Cyclooctatetraene Complexes of the Rare-Earth Elements: Synthesis, Structure, and Magnetism

Novel chiral rare-earth half sandwich
complexes containing the
chiral amidinate ligand, (S,S)-N,N′-bis­(1-phenylethyl)­benzamidinate
((S)-PEBA) or the tBu
analogue (S,S)-N,N′-bis­(1-phenylethyl) pivalamidinate ((S)-PETA) and the cyclooctatetraene dianion (C8H8)2– (COT) were synthesized. All complexes
were fully characterized and the solid state structures were established
by single-crystal crystallography. Magnetic property measurements
indicated that the complex [{(S)-PETA}­Er­(COT)­(THF)]
is a typical field-induced single-molecule magnet (SMM), of which
the magnetic properties are in reasonable agreement with high-level
quantum chemical calculations. Due to predominantly electrostatic
ligand field effects, the relativistic J = 15/2 ground
manifold of Er­(III) is split into 8 Kramers doublets spanning a range
of ∼500 cm–1, representable by means of higher
order spin tensor operators. According to the quantum chemical calculations
as well as from analysis of the experimental data, the magnetic relaxation
pathways in these complexes are most likely to be of vibrational rather
than electronic origin.