No abstract

Multiple iron atoms bridged by hydrides is a common structural feature of the active species that have been postulated in the biological and industrial reduction of N. In this study, the reactions of an Fe(II) amide complex with pinacolborane in the presence/absence of phosphines afforded a series of hydride-supported [Fe] and [Fe] clusters Fe(μ-H)(μ-H){N(SiMe)}(PR) (PR = PMe (2a), PMePh (2b), PEt (2c)), Fe(μ-H)(μ-H)(PMe) (3), and (η-CH)Fe(μ-H){μ-N(SiMe)}{N(SiMe)} (4), which were characterized crystallographically and spectroscopically. Under ambient conditions, these clusters catalyzed the silylation of N to furnish up to 160 ± 13 equiv of N(SiMe) per 2c (40 equiv per Fe atom) and 183 ± 18 equiv per 3 (31 equiv per Fe atom). With regard to the generation of the reactive species, dissociation of phosphine and hydride ligands from the [Fe] and [Fe] clusters was indicated, based on the results of the mass spectrometric analysis on the [Fe] cluster, as well as the formation of a diphenylsilane adduct of the [Fe] cluster.

N2 fixation by Nature, which is a crucial process to supply bio-available forms of nitrogen, is performed by nitrogenase. This enzyme employs a unique transition metal-sulfur-carbon cluster as its active-site cofactor ([(R-homocitrate)MoFe7S9C], FeMoco), 1,2 and the sulfur-surrounded Fe atoms have been postulated to capture and reduce N2. [3][4][5][6] Whereas synthetic counterparts of FeMoco, metal-sulfur clusters, have displayed binding of N2 in a few examples, 7,8 the reduction of N2 by any synthetic metal-sulfur clusters or even by the extracted form of FeMoco 9 have remained elusive despite a near-50-year history of research. Here we show that the Fe atoms in our synthetic [Mo3S4Fe] cubes 10,11 capture an N2 molecule and catalyze N2 silylation to form N(SiMe3)3 under treatment with excess Na and Me3SiCl. These results exemplify the first catalytic N2 reduction by a synthetic metal-sulfur cluster with an Fe center supported only by S ligands. This work demonstrates the N2-reducing capability of Fe atoms in a S-rich environment, which Nature has selected to accomplish a similar purpose. This work also suggests some critical features for successful N2 reduction by metal-sulfur compounds, which serve as clues to understand the origin of N2 fixation on Earth.

Sediment samples were obtained from areas of diffuse hydrothermal venting along the seabed in the Tonga sector of the Tonga-Kermadec Arc, southwest Pacific Ocean. Sediments from Volcano 1 and Volcano 19 were analyzed by X-ray diffraction (XRD) and found to be composed primarily of the iron oxyhydroxide mineral, two-line ferrihydrite. XRD also suggested the possible presence of minor amounts of more ordered iron (hydr)oxides (including six-line ferrihydrite, goethite/lepidocrocite and magnetite) in the biogenic iron oxides (BIOS) from Volcano 1; however, Mössbauer spectroscopy failed to detect any mineral phases more crystalline than two-line ferrihydrite. The minerals were precipitated on the surfaces of abundant filamentous microbial structures. Morphologically, some of these structures were similar in appearance to the known iron-oxidizing genus Mariprofundus spp., suggesting that the sediments are composed of biogenic iron oxides. At Volcano 19, an areally extensive, active vent field, the microbial cells appeared to be responsible for the formation of cohesive chimney-like structures of iron oxyhydroxide, 2-3 m in height, whereas at Volcano 1, an older vent field, no chimney-like structures were apparent. Iron reduction of the sediment material (i.e. BIOS) by Shewanella putrefaciens CN32 was measured, in vitro, as the ratio of [total Fe(II)]:[total Fe]. From this parameter, reduction rates were calculated for Volcano 1 BIOS (0.0521 day(-1)), Volcano 19 BIOS (0.0473 day(-1)), and hydrous ferric oxide, a synthetic two-line ferrihydrite (0.0224 day(-1)). Sediments from both BIOS sites were more easily reduced than synthetic ferrihydrite, which suggests that the decrease in effective surface area of the minerals within the sediments (due to the presence of the organic component) does not inhibit subsequent microbial reduction. These results indicate that natural, marine BIOS are easily reduced in the presence of dissimilatory iron-reducing bacteria, and that the use of common synthetic iron minerals to model their reduction may lead to a significant underestimation of their biological reactivity.

Abstract. Nanoparticle synthesis was performed using high-powered pulsemodulated induction thermal plasma (PMITP) technique to study the effect of coil current modulation on synthesized nanoparticles. This is the first paper to present a summary of results of TiO 2 nanoparticle synthesis using high-power Ar-O 2 PMITP at 20 kW. The synthesized particles were analyzed using a field emission scanning electron microscope (FE-SEM), and X-ray diffractometry (XRD). In addition, optical emission spectroscopy (OES) was used during nanoparticle synthesis experiments to measure TiO spectra and to determine the time-averaged vibrational and rotational temperatures of TiO in the reaction chamber. Results showed that the PMITP produced smaller nanoparticles and a narrower size distribution of particles. Moreover, PMITP provided a lower-temperature region in the reaction chamber downstream of the plasma torch than such regions in non-modulated thermal plasmas.