Metal clusters formed the basis of the first decade-plus of single-molecule magnet research, beginning with the archetype of single-molecule magnets, "Mn 12 ". This complex is a polymetallic manganese (Mn) complex having the formula [Mn 12 O 12 (OAc) 16 (H 2 O) 4 ], where OAc stands for acetate. It has the remarkable property of showing an extremely slow relaxation of their magnetization below a blocking temperature. [Mn 12 O 12 (OAc) 16 (H 2 O) 4 ]·4H 2 O·2AcOH, which is called "Mn 12 -acetate" is a common form of this used in research.