Magnetic properties of molecular clusters comprising twelve manganese ions

The magnetic properties of [Mn12O12(CH3COO)(16)(H2O)(4)], Mn12Ac, a mixed v alence cluster originally reported by the Wroclaw School are reviewed. This is the first molecular cluster which has been discovered to undergo slow r elaxation of the magnetization at low temperature. The relaxation time of t he magnetization follows a thermally activated behaviour down to 2 K and be low this the relaxation occurs through quantum tunneling. Another unique fe ature of the cluster is that it gives rise to magnetic hysteresis of purely molecular origin, opening the perspective of information storage in one mo lecule.