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 pathway...