Molecular Growth of a Core–Shell Polyoxometalate

Abstract

The self-assembly of large metal oxide clusters usually proceeds via condensation steps thermodynamically driven by charge and nucleophilicity of the growing transient cluster fragments. Polyoxometalate (POM) chemistry [1] has accumulated many strategies to interfere with these basic formation principles, aiming at both directed molecular growth and targeted functionalization by selective introduction of metal centers or organic moieties. POM structures integrating 3d or 4d transition-metal ions in particular attest to this approach, and they have led to a rich class of molecular materials [2] ranging from molecular magnets [3] to oxidation catalysts. [4] In this context, polyoxotungstate clusters provide rigid and redox-stable scaffolds based on building-block-type fragments that are frequently derived from archetypal structures such as the Keggin, Dawson, or Lindqvist species.[5] Additional heterometal cations coordinating to or interconnecting these nucleophilic structures are key to the reactivity and the electronic and magnetic characteristics of the resulting adducts.[6] This situation is exemplified by the spherical {M 72 L 30 } Keplerate clusters that have been realized both as polymolybdate (M = Mo) and polytungstate (M = W) structures containing a variety of heterometal linkers (L = V, Cr, Fe, etc.).[7] These clusters, comprising unique spin polytopes that represent molecular analogues of KagomØ lattices, constitute structural platforms for subsequent reactions, ranging from redox reactions [8] and partial heterometal exchange [9] to condensations to one-and two-dimensional coordination networks [10] -all of which alter the clusters magnetic characteristics while retaining the basic cluster structure. Moreover, recent development of POM-based single-molecule magnets [3] raises the hope that magnetic POMs may find their way into areas such as molecular spintronics or quantum computing.[11]However, the controlled growth of large metal oxide clusters remains elusive: precise prediction of the outcome is very difficult given the involvement of many, often labile, metal-oxygen bonds. The self-assembly mechanisms that underlie the formation of larger POMs in aqueous reaction solutions are barely established and are not compatible with the synthetic controls available in classical coordination chemistry, as exemplified by the use of molecular tectons, characterized by their specific connectivity constraints, in the rational production of supramolecular aggregates [12] or porous metal-organic frameworks. [13] We postulate that this roadblock in controlling the molecular growth steps in polyoxotungstate chemistry can be partially circumvented by kinetic control of competing reactions, as illustrated by the template-induced formation of a 4. [16] used widely as a source of Mn III ions in the synthesis of various molecular magnets, [17] leads to slow formation of black crystals of K 56 Li 74 H 14 1·ca.680 H 2 O (1 a) in an overall yield of 27 %.Compound 1 a crystallizes in the triclinic space group P1 with two ...

Soluble Hetero‐Polyoxovanadates and Their Solution Chemistry Analyzed by Electrospray Ionization Mass Spectrometry

“…Luban and co‐workers presented an intriguing example of a well‐ordered assembly from a total of 13 substructures . They combined a supramolecular templating effect and a kinetic competition approach to selectively generate the complex {Mn 40 W 224 } polyanionic architecture 1 , which was characterized by single‐crystal structure determination (Figure a).…”

“…Reprinted and adapted with permission from ref. (Copyright 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim).…”

Building Block Libraries and Structural Considerations in the Self-assembly of Polyoxometalate and Polyoxothiometalate Systems

“…The largest polyanion cluster isolated so far constructed using 12 ({P2W12}) [33]. The structure of {Mn40W224} shows how different archetypal building blocks can be assembled via a network of Mn-O = W bridges (Fig.…”

Synthesis, structure and electrochemical properties of a Fe III –Ce III heterometallic sandwich-type tungstoantimonate with novel 2-D infinite structure [Ce(H 2 O) 8 ][Ce(H 2 O) 6 ][Fe 4 (H 2 O) 10 (B-β-SbW 9 O 33 ) 2 ]·16H 2 O

“…The electrochemical and electrocatalytic properties of 1 have been systemically studied in 0.5 mol·L −1 Na 2 SO 4 + H 2 SO 4 supporting electrolyte, moreover, 1 exhibits the obvious electrocatalytic activity towards the reduction of BrO 3 − and NO 2 − . © 2015 Elsevier B.V. All rights reserved.With the specific oxygen-enriched surfaces, controllable sizes and high negative charges, lacunary polyoxometalate (POM) precursors are often selected as benign multidentate inorganic ligands to integrate oxophilic transition-metal (TM) or rare-earth (RE) cations into a great number of functional mental-oxo clusters in various fields such as catalysis, magnetism, photochemistry, medicine and materials science [1][2][3][4][5]. In the past several decades, numerous TM-substituted POMs (TMSPs) and RE-substituted POMs (RESPs) with neoteric structures have been dug out because of the extensive use of this assembly strategy of POM precursors.…”