Tuning symmetry and magnetic blocking of an exchange-coupled lanthanide ion in isomeric, tetrametallic complexes: [LnCl(6)(TiCp(2))(3)]

The synthesis and magnetic properties of two pairs of isomeric, exchange-coupled complexes, [LnCl(6)(TiCp(2))(3)] (Ln = Gd, Tb), are reported. In each isomeric pair, the central lanthanide ion adopts either a pseudo-octahedral (O-Ln) or trigonal prismatic geometry (TP-Ln) yielding complexes with C(1) or C(3h) molecular symmetry, respectively. Ferromagnetic exchange coupling is observed in TP-Ln as indicated by the increases in χ(m)T below 30 K. For TP-Gd, a fit to the susceptibility reveals ferromagnetic coupling between the Gd(3+) ion and the Ti(3+) ions (J = 2.90(1) cm(−1)). In contrast to O-Tb, which shows no single-molecule magnetic behavior, the TP-Tb complex presents slow magnetic relaxation with a 100s-blocking temperature of 2.3 K and remanent magnetization at zero field up to 3 K. The calculated electronic structures of both compounds imply that trigonal prismatic geometry of TP-Tb is critical to the observed magnetic behavior.