Assembly of Platinum Diimine Dithiolate Complexes onto Hydrogen-Terminated Silicon Surfaces

The synthesis and structural characterization
of the platinum diimine
dithiolate complexes [Pt­(R2bipy)­(dmipi)] (dmipi = 4,5-dimercapto-l,3-dithiol-2-propargylimino
and R = H, tBu) are described together with the X-ray
crystal structure of the dithiolate proligand. These heteroleptic
Pt complexes have been covalently bound to hydrogen-terminated silicon
(100) surfaces using either a one-step or two-step procedure. The
redox-active organometallic film modified surfaces were prepared from
a hydrosilylation reaction at 90 °C of either the Pt complex
bearing an ethyne terminal group or an ethyne-terminated dithiolate
precursor followed by the subsequent anchoring of the Pt complex.
Cyclic voltammetry measurements showed the presence of a single reversible
one-electron-oxidation process corresponding to the oxidation of the
complex into its radical cation species at 0.42 and 0.46 V vs SCE
for the unsubstituted and tBu-substituted bipyridine
dithiolate Pt complex-modified Si(100) surfaces, respectively. Such
values compare well with those determined for the electroactive molecules
in solution. Moreover, FTIR spectroscopy and X-ray photoelectron spectroscopy
(XPS) measurements were consistent with the expected structure of
grafted molecular chains and revealed a significant oxidation of the
underlying silicon surface. Nevertheless, the one-step procedure was
found to lead to redox-active films of density higher than those produced
from the two-step procedure. From XPS data, the surface coverage was
estimated at 0.10 and in the range 0.03–0.06 Pt complex per
surface silicon atom for the one-step and two-step procedures, respectively.