Metal Substitution in Keggin-Type Tridecameric Aluminum−Oxo−Hydroxy Clusters

Parker, Wallace O.; Millini, Roberto; Kiricsi, Imre

doi:10.1021/ic960635s

Cited by 93 publications

(92 citation statements)

References 36 publications

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“…The diffractograms were produced using supporting MDI Data Scan 4 and Jade 8 software packages. The identity of the crystalline selenate product was confirmed by comparison to the X-ray data of Johansson (11) and Parker et al (23).…”

Section: Methodssupporting

confidence: 61%

Energetics of Al ₁₃ Keggin cluster compounds

Armstrong

Casey

Navrotsky

2011

Proc. Natl. Acad. Sci. U.S.A.

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The ϵ-Al 13 Keggin aluminum hydroxide clusters are essential models in establishing molecular pathways for geochemical reactions. Enthalpies of formation are reported for two salts of aluminum centered ϵ-Keggin clusters, Al 13 The formation of both ε-Al 13 Keggin cluster compounds is exothermic from oxide-based components but energetically unfavorable with respect to a gibbsite-based assemblage. To understand the relative affinity of the ϵ-Keggin clusters for selenate and sulfate, the enthalpy associated with two S-Se exchange reactions was calculated. In the solid state, selenium is favored in the Al 13 compound relative to the binary chalcogenate, while in 5 N HCl, sulfur is energetically favored in the cluster compound compared to the aqueous solution. This contribution represents the first thermodynamic study of ε-Al 13 cluster compounds and establishes a method for other such molecules, including the substituted versions that have been created for kinetic studies. Underscoring the importance of ε-Al 13 clusters in natural and anthropogenic systems, these data provide conclusive thermodynamic evidence that the Al 13 Keggin cluster is a crucial intermediate species in the formation pathway from aqueous aluminum monomers to aluminum hydroxide precipitates.aluminum hydrolysis | polyoxocations F ew subjects are more central to geochemistry and materials science than aluminum hydrolysis chemistry. From a geochemist's perspective, aluminum hydrolysis products are key to mineral paragenesis and watershed chemistry. In addition, nanometer-size aluminum hydroxide molecules, including Al 13 ϵ-Keggin clusters, are critical to both experiment and simulation to detail possible reaction pathways at the solid-water interface (1). Aluminum clusters form complexes with a variety of reactive components including clay particles, natural organic matter, viruses, bacteria, and spores and thus are of interest to the environmental community for applications in water treatment and contaminant remediation technologies (2). Such clusters have also been used in a wide variety of industrial and consumer applications (3) and, because of their unique size and reactivity, they are effective as clay pillars (4) and catalysts (5).At near-neutral and higher pH, the dominant multimeric aluminum complex in aqueous systems is the large polycation, ½Al 12 ðAlO 4 ÞðOHÞ 24 ðH 2 OÞ 12 7þ , which forms quickly via Al 3þ hydrolysis and is a precursor to solid flocs (6). It consists of a central tetrahedrally coordinated AlO 4 moiety, enveloped by a sheath of 12 edge-shared AlO 6 units in four sets of three linked trimers. The most familiar form of this molecule, referred to as ε-Al 13 , has a structure identical to the ϵ-isomer of the BakerFiggis-Keggin structures (7-9). This isomer has edge-shared trimeric capping groups organized around a central tetrahedral AlO 4 site that is inert. Under favorable conditions, other isomers and larger clusters can be synthesized by hydrothermal reaction or by slow aging at room temperature (10).Because high-purit...

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Section: Methodssupporting

confidence: 61%

Energetics of Al ₁₃ Keggin cluster compounds

Armstrong

Casey

Navrotsky

2011

Proc. Natl. Acad. Sci. U.S.A.

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“…First, the Cr polycation Keggin ion (or related cluster) was long thought to exist as an aqueous specie, but prior attempts of its isolation proved unsuccessful. (Bradley et al, 1993) Second, Zn in the center of the Keggin ion was predicted to offer stabilization of polycationic Keggin ions; (Parker et al, 1997;Stewart et al, 2009) but again, this could not be proven without definite structural evidence. Isolation and structural characterization of Zn(CrAl)12 has now provided opportunity to probe via computation and experiment the stability of chromium polycations, as well as the effect of the Zn-center, the Zn-cap and more broadly, the relationship between capping Keggin ions and rotational isomerization.…”

Section: Discussionmentioning

confidence: 99%

Crystallizing Elusive Chromium Polycations

Wang

Fullmer

Bandeira

et al. 2016

Chem

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SUMMARYOxo and oxo-hydroxo metal clusters are commonly isolated from aqueous solutions with capping ligands to prevent precipitation of metal hydroxides. Few simple molecular oxo-hydroxo metal clusters are readily synthesized and isolated without these capping ligands. Yet uncapped clusters are important in metal oxide growth and for applications hindered by auxiliary ligands. Uncapped clusters containing transition metals with partially filled d shells are especially difficult to preparethey rapidly aggregate and precipitate, preventing isolation of the initial cluster form. Herein, we elucidate a cluster self-assembly and crystallization process that has yielded a new uncapped oxo-hydroxo cluster containing Zn 2+ , Al 3+ , and the open-shell transition metal ion Cr 3+ , i.e., [ZnO4Al5.1Cr6.9(OH)24(H2O)12Zn(H2O)3] 8+ . For decades, clusters of Cr 3+ and Zn 2+ have been synthesis targets in polyoxocation chemistry, but they have resisted isolation and crystallization. We control pHdriven hydrolysis by oxidative dissolution of zinc in the reaction solution, rather than by addition of hydroxide. The control gained by Zn dissolution allows metal nitrate concentrations 10× higher than conventional hydroxide addition. Therefore, a high nitrate concentration further suppresses cluster self-assembly in the bulk. Contrary to common cluster growth studies, the fully assembled cluster is not observed spectroscopically in the bulk reaction solution from which the clusters are crystallized. Instead, the reaction solution is dominated by monomeric and dimeric metal species, even while the solution actively grows crystals. Evaporation of the HNO3-H2O azeotrope at the solution surface allows simultaneous cluster self-assembly and crystallization. Because these reactive clusters do not accumulate in the bulk solution and are isolated by crystallization, the state that often results in uncontrolled precipitation of metal hydroxide is avoided. The proposed formation pathway opens new opportunities to explore and augment the composition space and reaction chemistry of compositionally complex oxo-hydroxo clusters, particularly those comprising metals with partially filled d shells. The Bigger PictureAqueous metal-oxide clusters are important in natural processes, in synthesis, and in technology. In nature, they are central to contaminant transport, mineral growth, photosynthesis, and biomineralization. In synthesis, they provide nanometric forms with size dependent properties, and they are pre-assembled building blocks for materials. Fabricating functional metal oxide clusters and cluster-based materials in water minimizes environmental impact. Clusters synthesized and manipulated in water provide understanding of natural processes and inspire biomimetic materials; i.e. for artificial photosynthesis.While synthesis of functional clusters is accomplished with great control in organic solvents; it doesn't offer the simplicity and sustainability of aqueous synthesis. But aqueous syntheses that provide well-controlled cluster and mate...

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“…The structure consists of a central metal ( IV M) in tetrahedral coordination to fourfold-coordinated oxygens ( 4 -O) that bond to four trimeric VI Al 3 O(OH) 3 (H 2 O) 9 groups (Johansson, 1960;Parker et al, 1997;Lee et al, 2001). These 4 -O are apparently inert to exchange.…”

Section: Introductionmentioning

confidence: 99%