Improved thermoelectric properties of nanostructured composites out of Bi1−xSbx nanoparticles and carbon phases

Thermoelectric figures of merit of ZT ≈ 0.4 at room temperature were achieved in nanostructured composite materials prepared by uniaxial pressing of Bi1−xSbx nanoparticles and 0.3 wt.% of a carbon phase. This constitutes a significant improvement of the low-temperature thermoelectric material Bi1−xSbx and strongly suggests the possibility of employing these materials in efficient thermoelectric devices working at room temperature. Interestingly, the beneficial effect of the carbon phase added to nanostructured Bi1−xSbx is the same for either carbon nanotubes or active carbon. This finding is attributed, on the one hand, to a combination of electronic band gap engineering due to nanostructuring and energy filtering due to graphene-like interlayers between Bi1−xSbx grains and, on the other hand, to modified phonon scattering at the grain boundaries and additional phonon scattering by agglomeration sites of carbon material on the μm scale

Improved thermoelectric properties of nanostructured composites out of Bi1−xSbx nanoparticles and carbon phases

Thermoelectric figures of merit of ZT ≈ 0.4 at room temperature were achieved in nanostructured composite materials prepared by uniaxial pressing of Bi1−xSbx nanoparticles and 0.3 wt.% of a carbon phase. This constitutes a significant improvement of the low-temperature thermoelectric material Bi1−xSbx and strongly suggests the possibility of employing these materials in efficient thermoelectric devices working at room temperature. Interestingly, the beneficial effect of the carbon phase added to nanostructured Bi1−xSbx is the same for either carbon nanotubes or active carbon. This finding is attributed, on the one hand, to a combination of electronic band gap engineering due to nanostructuring and energy filtering due to graphene-like interlayers between Bi1−xSbx grains and, on the other hand, to modified phonon scattering at the grain boundaries and additional phonon scattering by agglomeration sites of carbon material on the μm scale

Ammonium Pertechnetate in Mixtures of Trifluoromethanesulfonic Acid and Trifluoromethanesulfonic Anhydride

Ammonium pertechnetate reacts in mixtures of trifluoromethanesulfonic anhydride and trifluoromethanesulfonic acid under final formation of ammonium pentakis(trifluoromethanesulfonato)oxidotechnetate(V), (NH$_{4}$)$_{2}$ [TcO(OTf) $_{5}$]. The reaction proceeds only at exact concentrations and under the exclusion of air and moisture via pertechnetyl trifluoromethanesulfonate, [TcO$_{3}$(OTf)], and intermediate Tc$^{VI}$ species. $^{99}$Tc nuclear magnetic resonance (NMR) has been used to study the Tc$^{VII}$ compound and electron paramagnetic resonance (EPR), $^{99}$Tc NMR and X-ray absorption near-edge structure (XANES) experiments indicate the presence of the reduced technetium species. In moist air, (NH$_{4}$)2[TcO(OTf)5] slowly hydrolyses under formation of the tetrameric oxidotechnetate(V) (NH$_{4}$)$_{4}$ [{TcO(TcO$_{4}$)$_{4}$}$_{4}$] ⋅10 H$_{2}$O. Single-crystal X-ray crystallography was used to determine the solid-state structures. Additionally, UV/Vis absorption and IR spectra as well as quantum chemical calculations confirm the identity of the species

S6_{6}N2_{2}O15_{15} — A Nitrogen‐Poor Sulfur Nitride Oxide, and the Anhydride of Nitrido‐ tris ‐Sulfuric Acid

The reaction of hexachlorophosphazene, P$_3$N$_3$Cl$_6$, with SO$_3$ leads to the new sulfur nitride oxide S$_6$N$_2$O$_{15}$. The compound displays an extraordinarily low nitrogen content and exhibits a bicyclic cage structure according to the formulation N{S(O)$_2$O(O)$_2$S}$_3$N, with both nitrogen atoms in trigonal planar coordination of sulfur atoms. Interestingly, the new nitride oxide can be also seen as the anhydride of nitrido‐tris‐sulfuric acid, N(SO$_3$H)$_3$

Synthesis of Aromatic and Aliphatic Di-, Tri-, and Tetrasulfonic Acids

Oligosulfonic acids are promising linker compounds for coordination polymers and metal-organic frameworks, however, compared to their carboxylic acid congeners, often not readily accessible by established synthetic routes. This Account highlights the synthesis of recently developed aromatic and aliphatic di-, tri- and tetrasulfonic acids. While multiple electrophilic sulfonations of aromatic substrates are rather limited, the nucleophilic aromatic substitution including an intramolecular variant, the Newman-Kwart rearrangement, allows the flexible introduction of up to four sulfur-containing moieties at an aromatic ring. Sulfonic acids are then accessed by oxidation of thiols, thioethers, or thioesters either directly with hydrogen peroxide or in two steps with chlorine (generated in situ from N-chlorosuccinimide/hydrochloric acid) to furnish sulfochlorides which are subsequently hydrolyzed. In the aliphatic series, secondary alcohols as starting materials are converted into thioethers, thioesters, or thiocarbonates by nucleophilic substitutions, which are also subsequently oxidized to furnish sulfonic acids

S6N2O15-A Nitrogen-Poor Sulfur Nitride Oxide, and the Anhydride of Nitrido-tris-Sulfuric Acid

The reaction of hexachlorophosphazene, P3N3Cl6, with SO(3)leads to the new sulfur nitride oxide S6N2O15. The compound displays an extraordinarily low nitrogen content and exhibits a bicyclic cage structure according to the formulation N{S(O)(2)O(O)(2)S}(3)N, with both nitrogen atoms in trigonal planar coordination of sulfur atoms. Interestingly, the new nitride oxide can be also seen as the anhydride of nitrido-tris-sulfuric acid, N(SO3H)(3)

Tripodal methanetrisulfonate ligands in the trinuclear complex {Ni-3[CH(SO3)(3)](2)(NMP)(8)}

The reaction of Ni(OH)(2) and methanetrisulfonic acid trihydrate CH(SO3H)(3)center dot 3H(2)O (H(3)MTA center dot 3H(2)O) in N-methyl-pyrrolidone (NMP) leads to the trinuclear complex {Ni-3[MTA](2)(NMP)(8)] (triclinic, P (1) over bar, Z=1, a =946.25(3), b= 1073.24(3), c= 1518.27(4) pm, alpha = 72.193(2), beta = 87398(2), gamma = 89.389(2)degrees, V = 1466.49(7) x 10(6) pm(3)). The structural features of the methanetrisulfonate anions are tripodal as well as chelating coordination of the Ni2+ ions. The thermal analysis has shown that the compound is first losing NMP molecules and that the solvent-free methanetrisulfonate finally decomposes yielding Ni3S2

Biphenyl Sulfonic and Disulfonic Acids with Perfluorinated Alkyl Residues

Sulfonic acids serve as interesting, yet not intensively studied alternatives to carboxylic acids as linker units in coordination polymers. In this study, we present the synthesis of hybrid sulfonic acids with polar, rigid biphenyl moieties and disordered highly fluorinated alkyl chains. Consequently, eight biphenyl sulfonic and disulfonic acids with one or two perfluoroalkyl chains were prepared. The key steps within the synthesis include two palladium catalyzed C-C bond formations: The perfluoroalkyl residue is installed by Heck reaction (up to 91 %) using 1H,1H,2H-perfluorinated alkenes (C-6 and C-8) and the biphenyl unit is established by a Suzuki coupling (up to 88 %) of boronic acids bearing one or two protected thiol groups. Finally, these thiol groups are converted into the sulfonic acids by N-chlorosuccinimide mediated oxidation followed by hydrolysis of the respective sulfonyl chloride