Palladium nanoparticles passivated by metal-carbon covalent linkages

Stable palladium nanoparticles were prepared by the passivation of palladium-carbon covalent linkages by the reduction of diazonium derivatives. The resulting particles were characterized by TEM, UV-vis, FTIR, and NMR measurements. Interestingly, in electrochemical studies of the electronic conductivity of the particle solid ensembles, Pd-biphenyl particles exhibited metallic temperature dependence within the temperature range of 80 to 320 K; whereas the conductivity of Pd-decylphenyl particles showed a transition from semiconductor to metal at 180 K, manifested by their distinctly different temperature dependence. Control experiments with alkanethiolate-protected palladium nanoparticles in the same temperature range exhibited only semiconductor-like conductivity which increased with increasing temperature. The discrepancy was interpreted using Mott's model for metal-insulator transition and ascribed to the strong Pd-C interactions and low contact resistance, which facilitated the interparticle charge transfer.