Résumé
The first air-stable Ln(iii) organometallic mixed-ligand sandwich complexes TPPLnCp* (Ln = Y (1), Tb (2), Dy (3), Ho (4), and Er (5)) bearing both 5,10,15,20-tetraphenylporphyrinate (TPP) and pentamethylcyclopentadienide (Cp*) ligands were synthesized by the reactions of half-sandwich bis(o-N,N-dimethylaminobenzyl) precursors Cp*Ln(CH2C6H4NMe2-o)2 with equimolar amounts of 5,10,15,20-tetraphenylporphyrin (TPPH2) in toluene at ambient temperature and isolated in 62%-74% yields. X-ray analysis revealed the linear Cnt(Cp*)-Ln-Cnt(TPP) geometry with a bond angle close to 180 degrees, a Cnt(Cp*)-Ln bond distance ranging from 2.325 to 2.365 & Aring; and a Cnt(TPP)-Ln distance ranging from 1.012 to 1.063 & Aring;. These complexes demonstrated remarkable thermal and oxidative stability, being sublimable under vacuum above 290 degrees C without decomposition (similar to 5 x 10-2 Torr). Magnetic studies revealed field-induced single-molecule magnet (SMM) behavior for the Tb3+, Dy3+, and Er3+ derivatives. Theoretical investigations revealed the presence of only moderately axial g tensors, a small splitting within the ground multiplet, and significant mixing between different projections of the total angular momentum, all of which contribute to the disappointing SMM behavior. A quasi-spherical Ln3+ coordination environment created by the tetradentate TPP ligand and appreciable orbital interactions of its pi-conjugated system with the dysprosium 4f orbitals could introduce transverse components to the crystal field.