Initially, the Naphthalene thiol ligand was reacted with [Dy2CpMe2(nBu)]2 in solvents of diethyl ether at room temperature and 233 K, respectively, to give two kinds of structures, binuclear complexes [Dy(CpMe)2(NaphS)]2 and trinuclear complexes [Dy(CpMe)2(NaphS)]3. The dimer and trimer complexes are thermodynamic and kinetic products, respectively. Then, we tried to reduce the Naphthalene thiol ligand into radical by kinds of reducing agents, aiming to get radical bridged dimer or trimer. However, the results seem that it does not work maybe due to the thermal instability of the radical.
After that, we chose indigo as the ligand, obtaining the first lanthanide indigo complexes. The results reveal that the indigo ligand can be accessed in three different oxidation states, i.e. 2, 3 and 4 in 1Ln, 2Ln and 3Ln, respectively. Through the one-electron reduction of 1Ln to give 2Ln, a strong antiferromagnetic coupling of the lanthanide with the indigo radical can be induced. The exchange coupling constant of J = 11 cm-1 describing the interaction between Gd3+ and the radical ligand in 2Gd is one of the largest known for a lanthanide. Complexes 1Dy and 2Dy give rise to SMM behaviour in zero D.C. field, however the anisotropy barriers are modest and decrease slightly, and the hysteresis is hardly affected by the radical nature of the ligand. These observations demonstrate that directly coupled radical ligands in SMMs do not necessarily result in high magnetic blocking temperatures and hysteresis with coercivity, and that factors such as the hard/soft nature of the donor atoms and their formal charge are also important design criteria.
Finally, A bulky cyclopentadienide ligand, 1,2,4-tri(tert-butyl)cyclopentadienide, was opted to construct a discrete metallocenium cation of the type [(Cpttt)2Dy]+ which gives rise to unprecedented single-molecule magnet properties, including a record anisotropy barrier and, more notably, magnetic blocking temperatures and coercivity that far exceed those described for all previous SMMs. Having established a new benchmark in molecular magnetism that pushes the blocking temperature much closer to the symbolic temperature of 77 K, the next challenge is to develop new SMMs with properties that exceed those of [(Cpttt)2Dy]+.
