Antimony States Research Articles

Fluorinated Antimony(V) Tetraarylporphyrins as High-Valent Electron Acceptors with Unparalleled Reduction Potentials

A series of fluorinated antimony(V) porphyrins, SbTPP(OMe)2·PF6, SbTPP(OTFE)2·PF6, SbT(4F)PP(OMe)2·PF6, SbT(35F)PP(OMe)2·PF6, SbT(345F)PP(OMe)2·PF6, SbT(4CF3)PP(OMe)2·PF6, SbT(35CF3)PP(OMe)2·PF6, and SbT(35CF3)PP(OTFE)2·PF6, have been synthesized with phenyl [P], 4-fluorophenyl [(4F)P], 3,5-difluorophenyl [(35F)P], 3,4,5-difluorophenyl [(345F)P], 4-trifluoromethylphenyl [(4CF3)P], and 3,5-bis(trifluoromethyl)phenyl [(35CF3)P], in the meso-positions. Additionally, the SbTPP(OTFE)2·PF6 and SbT(35CF3)PP(OTFE)2·PF6 carry trifluoroethoxy units in their axial-positions. The fluorination on the porphyrin peripherals ranges from zero fluorine atoms in SbTPP(OMe)2·PF6 to 30 fluorine atoms in SbT(35CF3)PP(OTFE)2·PF6. X-ray crystallography confirmed the structures of the investigated antimony(V) porphyrins. The absorption spectra depend on the number of fluorine atoms as it is blue-shifted with increasing fluorination. The series also exhibited rich redox chemistry with two reduction processes and one oxidation process. Remarkably, these porphyrins manifested the lowest reduction potentials reported among the main-group porphyrins, which are as low as -0.08 V vs SCE for SbT(35CF3)PP(OTFE)2·PF6. On the contrary, the oxidation potentials were found to be very large, that is equal to 2.20 V vs SCE or even higher for SbT(4CF3)PP(OMe)2·PF6 or SbT(35CF3)PP(OMe)2·PF6 and SbT(35CF3)PP(OTFE)2·PF6, respectively. These unprecedented potentials are due to a combination of two factors: (i) the +5-oxidation state of antimony in the porphyrin cavity and (ii) the presence of the strong electron-withdrawing fluorine atoms on the porphyrin peripherals. Density functional theory (DFT) calculations were used to support the experimental results. The systematic study of antimony(V) porphyrins, especially their high potentials, make them ideal for the construction of photoelectrodes and excellent electron acceptors for photoelectrochemical cells and artificial photosynthetic systems, respectively, for solar energy conversion and storage applications.

Using the Mössbauer spectroscopy of 121Sb nuclei to differentiate the effects of Cr and Sb co-dopants on the photocatalytic activity of anatase-type polycrystalline TiO2 powders

The rates of the photocatalytic decolorization of methyl orange solutions in the presence of anatase powders modified by Cr3+ and Sb5+ co-dopants are compared with allowance for data on the actual valence state of antimony in the catalyst, obtained using 121Sb Mossbauer spectroscopy. The reported results point to the catalytic activity of the Cr6+ ions formed to compensate for the Cr3+ charge deficit in antimony-free samples.

Isolation and Characterization of Antimony-Reducing Bacteria from Sediments Collected in the Vicinity of an Antimony Factory

To date, there is very little information available on the oxidation and reduction of antimony by bacteria. An antimonate-respiring bacterium was isolated from sediment samples collected in the vicinity of an antimony oxide-producing factory in Korea. This bacterium was isolated by application of the Hungate standard anaerobic culture technique. Temporarily named strain JUK-1, it was found to be a rod-shaped bacterium and occurred individually or in pairs. Antimonate (pentavalent antimony) was reduced to antimonite (trivalent antimony) in the presence of JUK-1 in an anoxic minimal medium containing 5 mM antimonate and 10 mM acetate. The organism grew optimally at an initial pH of 7.7 and a temperature of 30°C. A part of the antimonite which was produced in medium precipitated as a bio-mineral containing approximately 50.0% antimony, 33.5% oxygen, 12.7% carbon, 2.0% sodium and 1.9% magnesium by weight. Based on the phylogenetics of 16S rRNA gene sequence and DNA G+C content, JUK-1 appears to be a new strain of the Sinorhizobium genus. The results suggest that bacteria may play a significant role in changing the redox state of antimony in the environment.

Determination of the oxidation state of antimony, iron and vanadium in mixed vanadium and iron antimonate oxide catalysts

Vanadium and mixed vanadium and iron antimonates with rutile-type structures have been studied by XANES at Sb L1 edge, 57Fe Mossbauer spectroscopy and ESR spectroscopy at 77 K. The results showed that both antimony and iron remained at their highest oxidation state, i.e. SbV and FeIII, whereas vanadium was present as VIII and VIV. Two types of VIV species were distinguished corresponding to well-isolated vanadyl species in distorted octahedral coordination and vanadyl species in the same coordination but close to each other and in a dipole–dipole interaction. Both VIII and total VIV concentrations decreased when the iron content increased, whereas isolated VIV concentration increased first and then decreased, with a maximum for x = 0.2 in FexV1-xSbO4. The observed variations in cationic composition are discussed in relation with the catalytic properties of the compounds in the ammoxidation of propane. Isolated VIV-O moieties appeared to be the most active and selective catalytic sites.

121Sb Mössbauer spectra of alkali metal antimonides M3Sb (M3 = Na3, K3, Na2K, Rb3)

121Sb Mossbauer spectra for M3Sb (M3 = Na3, K3, Na2K, Rb3) were measured at 12 K. The values of isomer shift (d) and quadrupole coupling constant suggest that the valence state of antimony in M3Sb is −3. The d values increase in the order Rb3Sb<K3Sb<Na3Sb<Na2KSb. The differences in d values are discussed by examining M–Sb distances and bond valence for M–Sb interactions. Some covalent interactions between alkali metal atoms and antimony atom are suggested.

A 121 Sb Mössbauer Study of the Chemical State of Antimony in V-Sb-O Mixed-Oxide Catalysts for the Ammoxidation of Propane

The structural changes of two representative samples of a group of V-Sb-oxide catalysts, a vanadium-rich and an antimony-rich specimen, are investigated by 121Sb Mossbauer spectroscopy after treatment under propene or hydrogen at 673 K. The as-prepared catalysts contain both Sb(V) and Sb(III) as crystalline and microcrystalline α-Sb2O4 and VSbO4, as well as an additional amorphous V5+ oxide phase. The oxidation state of antimony does not change upon exposure to propene, whereas a partial reduction can be obtained by a more intense reduction under hydrogen. The Mossbauer results indicate that the antimony in VSbO4 can be reduced more easily than that in α-Sb2O4, which appears to be more stable. These results are discussed in view of the observed depletion of vanadium at the surface of the catalyst particles under reaction conditions.

M�ssbauer spectroscopic study of the oxidation state of antimony in antimony sulfides of different composition

M�ssbauer spectroscopic study of the oxidation state of antimony in antimony sulfides of different composition

The +1 oxidation state of antimony

The reaction of antimony with arsenic pentafluoride in liquid SO2 produces a compound formulated as (Sbnn+)(AsF6–)n.