Films of monolayer protected Au clusters (MPCs) with mixed alkanethiolate and omega-carboxylate alkanethiolate monolayers, linked together in a network polymer by carboxylate-Cu2+-carboxylate bridges, exhibit electronic conductivities (sigma(EL)) that vary with both the numbers of methylene segments in the ligands and the bathing medium (N2, liquid or vapor). A chainlength-dependent swelling/contraction of the film's internal structure is shown to account for changes in sigma(EL). The linker chains appear to have sufficient flexibility to collapse and fold with varied degrees of film swelling or dryness. Conductivity is most influenced (exponentially dependent) by the chainlength of the nonlinker (alkanethiolate) ligands, a result consistent with electron tunneling through the alkanethiolate chains and nonbonded contacts between those chains on individual, adjacent MPCs. The sigma(EL) results concur with the behavior of UV-vis surface plasmon adsorption bands, which are enhanced for short nonlinker ligands and when the films are dry. The film conductivities respond to exposure to organic vapors, decreasing in electronic conductivity and increasing in mass (quartz crystal microgravimetry, QCM). In the presence of organic vapor, the flexible network of linked nanoparticles allows for a swelling-induced alteration in either length or chemical nature of electron tunneling pathways or both.
Interfacial oxidation and reduction of Prussian Blue (PB), KFe III [Fe II (CN) 6 ]‚nH 2 O (n ≈ 10), powder were probed in situ with Fourier transform infrared attenuated total reflection (FT-IR/ATR) spectroscopy. The combination of electrochemistry in the absence of liquid electrolyte with internal reflectance FT-IR spectroscopy was accomplished using a simple two-electrode sandwich-type cell in which a crystalline germanium served both as a working electrode and an infrared transparent element. Application of sufficiently large potential differences to sandwich electrodes led to oxidation and reduction of PB at opposing interfaces. The spectra, which were monitored by difference, clearly show changes in the cyanide stretching frequency range upon oxidation and reduction.
Oxidized and reduced cobalt(II) hexacyanoferrates were
fabricated and characterized in the presence of alkali
metal (Li+, Na+, K+,
Cs+) and Co2+ countercations. Formal
potentials of hexacyanoferrate(III,II) redox
reactions are sensitive to the choice of electrolyte cation, and they
correlate well with the sizes of hydrated
Li+, Na+, and K+.
Electrochemical quartz crystal microbalance measurements clearly
indicate that
countercations, presumably in partially dehydrated form, are
incorporated into reduced cobalt(II) hexacyanoferrate(II). The color of the system reflects primarily the
oxidation state of iron sites. But the color of
the reduced form is also affected by the nature of an intercalated
hydrated countercation. This observation
is correlated with the reversible continuous thermochromism of
K2CoII[FeII(CN)6]*nH2O
that shall be attributed
to the release of structural water molecules interacting with
CoII during heating in the temperature range
25−85 °C. It is apparent from X-ray absorption near-edge
structure (XANES) experiments that the chemical
environment of cobalt(II) sites is influenced by the presence of
hydrated alkali metal countercations. The
results are consistent with the accommodation of countercations in the
lattice cavities at interstitial positions.
The structural environment of iron ions was the same in all
systems studied except that a chemical shift was
observed due to change of the oxidation state of iron.
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