The electronic quantum size effect observed by195Pt NMR in the metal cluster compound Pt309Phen 36 * O30

195Pt NMR on the organic ligand stabilized metal cluster compound Pt309Phen 36 * O30 reveals two separate peaks in the lineshape. Ligand-bonded platinum atoms at the surface of the core are thought to be responsible for the peak that does not show any Knight shift. The corresponding spin-lattice relaxation timeT1 is of the order of seconds. The second peak is Knight shifted and is attributed to the other Pt atoms, for which metallic behavior is inferred from the temperature dependence ofT1. The Korringa relation holds down to 65 K. Below 65 K the relaxation of the magnetization becomes increasingly non-exponential with decreasing temperature. The relaxation process can be successfully modelled under the assumption of a Poisson distribution of the energy levels around the Fermi energy (the electronic quantum size effect).