The UV−vis spectroscopy and cyclic voltammetry of
2,5-dimercapto-1,3,4-thiadiazole (DMcT) were studied
in the absence and presence of pyridine (Py) or triethylamine (TEA) in
acetonitrile solutions in order to
examine the influence of acid−base processes on the redox behavior of
DMcT. In solutions containing Py,
DMcT can be singly deprotonated to give the anionic species,
DMcT-. In solutions containing TEA,
DMcT
can be either singly or doubly deprotonated to give the anionic
species, DMcT-, or the dianion,
DMcT2-,
depending on the stoichiometry. These acid−base processes were
monitored using UV−vis spectroscopy,
and those results are reported here. The cyclic voltammetry of
both systems was also examined in the absence
and presence of Py or TEA. These experiments clearly showed that
deprotonation of DMcT results in
facilitation of its electrochemical oxidation, leading either to a
disulfide-containing dimer or a disulfide-containing polymer, depending on conditions. The relevance of these
results to the use of DMcT as a cathode
material in lithium secondary batteries is discussed.
The effects of pyridine and several derivatives
(3-chloropyridine and lutidine) on the redox reactions of
2,5-dimercapto-1,3,4-thiadiazole (DMcT) and the disulfide dimer of DMcT have
been examined using cyclic
voltammetry and UV−vis spectroscopy. In the presence of these
bases, the oxidative coupling reactions of
DMcT and its disulfide dimer to give a disulfide-containing polymer are
facilitated, presumably due to proton-transfer processes with the bases. The potentials at which the
oxidative polymerization and reductive
depolymerization occur in the presence and absence of such proton
transfer reagents are discussed. Also, it
is observed that the oxidation of DMcT is facilitated in the presence
of DMSO or NMP. The relevance of
these results to the possible use of DMcT/polyaniline composite
materials as a cathode material in secondary
lithium batteries is discussed, especially with regard to the
potentials at which the various redox processes
can occur.
The synthesis and characterization of poly(thiophenylenesulfonic
acid), a novel class of
polyaromatic electrolyte possessing up to 2.0 sulfonic acid groups per
phenylene unit (m = 2.0), are
described. 4-(Methylsulfinyl)diphenyl sulfide (1) was
polymerized in sulfuric acid upon heating (<140
°C) or in the presence of SO3 to yield a sulfonated
poly(sulfonium cation) (4), which can be converted
to
the corresponding sulfonated poly(thiophenylene). The precursor
method using the soluble poly(sulfonium
cation) makes it easy to control the sulfonation reaction in a
homogeneous system. The resulting
poly(thiophenylenesulfonic acid), unlike the nonsubstituted polymer, is
soluble in water and methanol
and can form a transparent film. The sulfonated polymer exhibits a
good water affinity and an excellent
proton conductivity due to the high carrier concentration. The
highest conductivity (σ = 4.5 × 10-2
S
cm-1) was achieved for the polymer with m =
2.0 at 80 °C.
A method is described by which the disulfide dimer of 2,5-dimercapto-1,3,4-thiadiazole (diDMcT, see
Scheme 1) can be oxidatively intercalated into the layered structure of a V2O5 xerogel. This intercalation
reaction produces a new organic−inorganic composite material with a layer spacing of 13.5 Å, in contrast
to the 11.55 Å spacing for the parent V2O5 xerogel. During this oxidative intercalation, the diDMcT is
polymerized to produce a polymer with thiadiazole rings linked by disulfides in the polymer main chain
(PDTT, see Scheme 1). The composite material is characterized by UV−visible spectroelectrochemistry,
X-ray diffraction, FTIR, and electrochemistry. The electrochemical experiments comprised charging
(oxidation) and discharging (reduction) of the material, with the bulk of the redox reaction occurring over
a broad potential range of 0.5 to −0.6 V versus saturated calomel electrode. The cyclic voltammogram of
the composite material shows features that can be attributed to the DMcT−PDTT redox response. However,
during or after reduction of the composite, the monomeric DMcT dithiolate appears to be expelled from
the V2O5 interlayer region, leading to an evolution of the electrochemical response back to that of the
original V2O5 material. Evidence is presented suggesting that the V2O5 host material facilitates the redox
reactions of the thiol−disulfide redox couple while it is within the interlayer region.
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