Preparation and characterization of Cr(CO)₄dpp (chromium tetracarbonyl 2,3-bis(2′-pyridyl)pyrazine) adsorbed on silver nanoparticles

A transition metal carbonyl species, Cr(CO)₄dpp, has been successfully attached to bare silver nanoparticles prepared by laser ablation of a metal foil in ethanol. Transmission electron microscopy (TEM) images have shown that at least a portion of the silver nanoparticles have been capped by the chromium species, and ligand shells corresponding to Cr(CO)₄dpp multilayer adsorption onto the silver nanoparticles of 30-50 nm diameter have been observed. The detection of the strongest Raman-active v_CO band of Cr(CO)₄dpp at 2004 cm^-1 revealed that the species has been adsorbed without decomposition. The time-of-flight secondary ion mass spectrometry (TOF-SIMS) signals recorded of the chromium-capped silver nanoparticles were also consistent with the nondecomposition adsorption process. Density functional calculations have been used to reproduce the Raman spectrum using Ag⁷⁺ as a model surface. A large binding energy of about 122 kJ/mol has also been computed between silver and nitrogen atoms thus lending support to Cr(CO)₄dpp being chemisorbed onto the silver surface.