Search

Lindqvist polyoxovanadate‐alkoxide (POV‐alkoxide) clusters are excellent candidates for applications in energy storage and conversion due to their rich electrochemical profiles. One approach to tune the redox properties of these cluster complexes is through substitutional cationic doping within the hexavanadate core. Here, we report the synthesis of a series of tungsten‐substituted POV‐alkoxide clusters with one and two tungsten atoms. Soft landing of mass‐selected ions was used to purify heterometal POV‐alkoxides that cannot be readily separated using conventional approaches. The soft landed POV‐alkoxides are characterized using infrared reflection‐absorption spectroscopy and electrospray ionization mass spectrometry. The redox properties of the isolated ions are examined using an in situ electrochemical cell which enables traditional in vacuo electrochemical measurements inside of an ion soft landing instrument. Although the overall cluster core retains redox activity after tungsten doping, vanadium‐based redox couples (VV/VIV) are shifted substantially, indicating a pronounced effect of a heteroatom on the electronic structure of the core. [ABSTRACT FROM AUTHOR]

Atom-by-atom substitution is a promising strategy for tailoring the electronic properties of transition metal oxide clusters. This approach typically generates a mixture of species that are difficult to separate using conventional methods. As a result, the characterization of their structures and electronic properties remains challenging. Herein, we use collision-induced dissociation (CID) to study the fragmentation of well-defined Fe- and W-doped Lindquist polyoxovanadate methoxides synthesized as a mixture of singly and doubly substituted species. Fragmentation reveals that Fe heteroatoms are efficiently retained within the metal oxide core. In contrast, one W atom is incorporated into the primary WO 2 (OCH 3) 2 neutral loss from both the singly and doubly substituted W-containing clusters. Collision energy-resolved CID provides insights into the fragmentation pathways, which are compared to those of the homometallic polyoxovanadate methoxide species. The incorporation of Fe into the cluster reduces its stability towards fragmentation, which could be attributed to the increase in the relative stability of Fe-containing fragment ions with four metal atoms in comparison with their homometallic analog. The observed fragmentation is rationalized by assuming that Fe atoms are incorporated within the low valent plane, while one W atom occupies the axial out-of-plane position in the cluster. [Display omitted] • Structural characterization of isolated Polyoxovanadate Alkoxides. • Cluster stability probed using collision energy resolved fragmentation data. • Heteroatom substitution into the low valent plane or out-of-plane axial position is distinguished. [ABSTRACT FROM AUTHOR]

Here, we expand on the synthesis and characterization of chloride-functionalized polyoxovanadate-alkoxide (POV-alkoxide) clusters, to include the halogenation of mixed-valent vanadium oxide assemblies. These findings build on our previously disclosed results describing the preparation of a mono-anionic chloride-functionalized cluster, [V6O6Cl(OC2H5)12]1−, by chlorination of [V6O7(OC2H5)12]2− with AlCl3, aimed at understanding the electronic consequences of the introduction of halide-defects in bulk metal oxides (e.g. VO2). While chlorination of the mixed-valent POV-ethoxide clusters was not possible using AlCl3, we have found that the chloride-substituted oxidized derivatives of the Lindqvist vanadium-oxide clusters can be formed using TiCl3(thf)3 with [V6O7(OC2H5)12]n (n = 1−, 0) or WCl6 with [V6O7(OC2H5)12]0. Characterization of the chloride-containing products, [V6O6Cl(OC2H5)12]n (n = 0, 1+), was accomplished via1H NMR spectroscopy, X-ray crystallography, and elemental analysis. Electronic analysis of the redox series of Cl-doped POV-alkoxide clusters via infrared and electronic absorption spectroscopies revealed all redox events are localized to the vanadyl portion of the cluster, with the site differentiated VIII–Cl moiety retaining its reduced oxidation state across a 1.9 V window. These results present new synthetic routes for accessing chloride-doped POV-alkoxide clusters from mixed-valent vanadium oxide precursors. [ABSTRACT FROM AUTHOR]

Reducible metal oxides (RMOs) are widely used materials in heterogeneous catalysis due to their ability to facilitate the conversion of energy-poor substrates to energy-rich chemical fuels and feedstocks. Theoretical investigations have modeled the role of RMOs in catalysis and found they traditionally follow a mechanism in which the generation of oxygen-atom vacancies is crucial for the high activity of these solid supports. However, limited spectroscopic techniques for in situ analysis renders the identification of the reactivity of individual oxygen-atom vacancies on RMOs challenging. These obstacles can be circumvented through the use of homogeneous complexes as molecular models for metal oxides, such as polyoxometalates. Summarized herein, a sub-class of polyoxometalates, polyoxovanadate–alkoxide clusters, ([V6O7(OR)12]n; R = CH3, C2H5; n = 2−, 1−, 0), are explored as homogeneous molecular models for bulk vanadium oxide. A series of synthetic strategies have been employed to access oxygen-deficient vanadium oxide assemblies, including addition of V(Mes)3(thf), tertiary phosphanes, and organic acids to plenary Lindqvist motifs. We further detail investigations surrounding the ability of these oxygen-deficient sites to mediate reductive transformations such as O2 and NOx1− (x = 2, 3) activation. [ABSTRACT FROM AUTHOR]

A low-valent [FeN5(OTf)2] complex and its bisnitrite adduct, [FeN5(NO2)2], have been synthesized in the interest of extending the reactivity of Fe complexes featuring redox-active ligands with secondary coordination sphere hydrogen-bond donors to nitrite reduction. Crystallographic characterization of [FeN5(NO2)2] reveals that the nitrite ligands demonstrate both ɳ1-NO2 (N-nitro) and ɳ1-ONO (O-nitrito) coordination modes. H-bonding between nitrite ligands and the protons on secondary amine moieties in the N5 ligand play a pivotal role in positioning the nitrite ligands in multiple coordination modes. These results provide insights into the role of H-bonding in supporting disparate coordination modes of this substrate that can be translated to mechanisms of nitrite reduction in biological systems. [ABSTRACT FROM AUTHOR]

We report the activation of nitrogen-containing oxyanions using an oxygen-deficient polyoxovanadate–alkoxide cluster. Reduction of NO21− and NO31− results in near-quantitative oxygen atom transfer to the coordinatively unsaturated VIII ion, and selective formation of NO. These results provide insight into possible mechanisms of oxyanion reduction by polyoxometalates. [ABSTRACT FROM AUTHOR]

Herein we report the use of manganese(II) chloride for the catalytic generation of C(sp²)-C(sp³) bonds via Kumada cross-coupling. Rapid and selective formation of 2-alkylated N-heterocyclic complexes were observed in high yields with use of 3 mol% MnCl2THF1.6 and under ambient reaction conditions (21 °C, 15 min to 20 h). Manganese-catalyzed cross-coupling is tolerant toward both electron-donating and electron-withdrawing functional groups in the 5-position of the pyridine ring, with the latter resulting in an increased reaction rate and a decrease in the amount of nucleophile required. The use of this biologically and environmentally benign metal salt as a catalyst for C-C bond formation highlights its potential as a catalyst for the late-stage functionalization of pharmaceutically active N-heterocyclic molecules (e.g., pyridine, pyrazine). [ABSTRACT FROM AUTHOR]

Titania-supported ruthenium (Ru/TiO 2) is an established catalyst for the hydrogenation of carbon dioxide to methane (Sabatier reaction). Chlorine contamination, owed to the RuCl 3 precursor, is demonstrated to have a detrimental impact on methanation activity. After calcination and reduction the catalyst contains residual chlorine, shown by XPS. An aqueous ammonia wash removes Cl without leaching Ru. The washed catalysts exhibit improvements in CH 4 site-time yields. Low Ru loading catalysts encounter the greatest activity enhancements after washing (∼4.5–fold). DFT calculations indicate that chlorine and CO 2 directly compete for adsorption on Ru step sites, with Cl impeding the adsorption of CO 2 at under-coordinated sites and at higher Cl coverages. H 2 -chemisorption/TPR show that Cl removal lowers the onset of low temperature H 2 dissociation on Ru. DRIFTS provide evidence that the removal of Cl facilitates low temperature dissociative binding of CO 2 , indicated by the formation of surface bound linear CO species. [Display omitted] ● Ru/TiO 2 methanation catalysts were synthesized from RuCl 3. ● An aqueous NH 3 wash removed Cl from the catalyst without leaching Ru. ● Unwashed and washed catalysts were morphologically similar. ● Washed catalysts were ∼4.5x more active than unwashed catalysts. ● Cl blocks the Ru sites that are essential for CO 2 methanation. [ABSTRACT FROM AUTHOR]

The rational control of the electrochemical properties of polyoxovanadate‐alkoxide clusters is dependent on understanding the influence of various synthetic modifications on the overall redox processes of these systems. In this work, the electronic consequences of ligand substitution at the heteroion in a heterometal‐functionalized cluster was examined. The redox properties of [V5O6(OCH3)12FeCl] (1‐[V5FeCl]) and [V5O6(OCH3)12Fe]X (2‐[V5Fe]X; X=ClO4, OTf) were compared in order to assess the effects of changing the coordination environment around the iron center on the electrochemical properties of the cluster. Coordination of a chloride anion to iron leads to an anodic shift in redox events. Theoretical modelling of the electronic structure of these heterometal‐functionalized clusters reveals that differences in the redox profiles of 1‐[V5FeCl] and 2‐[V5Fe]X arise from changes in the number of ligands surrounding the iron center (e.g. 6‐coordinate vs. 5‐coordinate). Specifically, binding of the chloride to the sixth coordination site appears to change the orbital interaction between the iron and the delocalized electronic structure of the mixed‐valent polyoxovanadate core. Tuning the heterometal coordination environment can therefore be used to modulate the redox properties of the whole cluster. [ABSTRACT FROM AUTHOR]