THE ELECTRONIC QUANTUM-SIZE EFFECT OBSERVED BY PT-195 NMR IN THE METAL CLUSTER COMPOUND PT309PHEN36-ASTERISK-O30

Pt-195 NMR on the organic ligand stabilized metal cluster compound Pt3 09Phen36O30 reveals two separate peaks in the lineshape. Ligand-bonde d platinum atoms at the surface of the core are thought to be responsi ble for the peak that does not show any Knight shift. The correspondin g spin-lattice relaxation time T1 is of the order of seconds. The seco nd peak is Knight shifted and is attributed to the other Pt atoms, for which metallic behavior is inferred from the temperature dependence o f T1. The Korringa relation holds down to 65 K. Below 65 K the relaxat ion of the magnetization becomes increasingly non-exponential with dec reasing temperature. The relaxation process can be successfully modell ed under the assumption of a Poisson distribution of the energy levels around the Fermi energy (the electronic quantum size effect).