We investigate the properties of long-chain alkyl xanthate-capped platinum nanoparticles. First an
uncapped platinum colloid, 4.0 ± 1 nm in diameter, is produced in an aqueous phase, and then the capping
agent is added. The capped particles are hydrophobic and easily transfer into organic solvents. They can
be dried and repetitively transferred to various organic liquids in a reversible manner. Xanthate-capped
platinum colloids are more stable than the analogous thiol-capped particles (and certainly noncapped
particles) toward chemical corrosion (by oxygen in the presence of cyanide ion) and are also stable on
heating. These colloids exhibit a characteristic sharp absorption in the range 450−470 nm in addition to
the extinction in the UV. This absorption might be assigned tentatively to a weak d−d transition of
platinum observed in this region also for the PtCl6
2- salt and for its adduct with xanthate, though it is
absent for uncapped Pt particles. The transition for the capped colloid, however, is much stronger compared
to that observed for the salts.
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