Stable chromium, molybdenum and tungsten nanoparticles are obtained reproducibly by thermal or photolytic decomposition under argon from mononuclear metal carbonyl precursors M(CO)6 (M = Cr, Mo, W) suspended in the ionic liquids BMim+BF4−, BMim+OTf− and BtMA+Tf2N− (BMim+ = n-butyl-methyl-imidazolium, BtMA+ = n-butyl-trimethyl-ammonium, Tf2N = N(O2SCF3)2, OTf = O3SCF3) with a very small and uniform size of 1 to 1.5 nm in BMim+BF4− which increases with the molecular volume of the ionic liquid anion to ∼100 nm in BtMA+Tf2N− [characterization by transmission electron microscopy (TEM), dynamic light scattering and transmission electron diffraction (TED) analysis].

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