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Interaction of Chromium(III) with a N,N'-Disubstituted Hydroxylamine-(diamido) Ligand: A Combined Experimental and Theoretical Study.
Inorg Chem
PUBLISHED: 10-20-2014
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Reaction of hydroxylamine hydrochloride with prop-2-enamide in dichloromethane in the presence of triethylamine resulted in the isolation of the N,N'-disubstituted hydroxylamine-(diamido) ligand, 3,3'-(hydroxyazanediyl)dipropanamide (Hhydia). The ligand Hhydia was characterized by multinuclear NMR, high-resolution electrospray ionization mass spectrometry (ESI-MS), and X-ray structure analysis. Interaction of Hhydia with trans-[Cr(III)Cl2(H2O)4]Cl·2H2O in ethanol yields the ionization isomers [Cr(III)(Hhydia)2]Cl3·2H2O(1·2H2O) and cis/trans-[Cr(III)Cl2(Hhydia)2]Cl·2H2O (2·2H2O). The X-ray structure analysis of 1 revealed that the chromium atom in [Cr(III)(Hhydia)2](3+) is bonded to two neutral tridentate O,N,O-Hhydia ligands. The twist angle, ?, in [Cr(III)(Hhydia)2](3+) is 54.5(6)(0), that is, very close to an ideal octahedron. The intramolecular hydrogen bonds developed between the N-OH group of the first ligand and the amidic oxygen atom of the second ligand and vice versa contribute to the overall stability of the cation [Cr(III)(Hhydia)2](3+). The reaction rate constant of the formation of Cr(III) complexes 1·2H2O and 2·2H2O was found to be 8.7(±0.8) × 10(-5) M(-1) s(-1) at 25 °C in methyl alcohol and follows a first-order law kinetics based on the biologically relevant ligand Hhydia. The reaction rate constant is considerably faster in comparison with the corresponding water exchange rate constant for the hydrated chromium(III). The modification of the kinetics is of fundamental importance for the chromium(III) chemistry in biological systems. Ultraviolet-visible and electron paramagnetic resonance studies, both in solution and in the solid state, ESI-MS, and conductivity measurements support the fact that, irrespective of the solvent used in the interaction of Hhydia with trans-[Cr(III)Cl2(H2O)4]Cl·2H2O, the ionization isomers[Cr(III)(Hhydia)2]Cl3·2H2O (1·2H2O) and cis/trans-[Cr(III)Cl2(Hhydia)2]Cl·2H2O (2·2H2O) are produced.The reaction medium affects only the relevant percentage of the isomers in the solid state. The thermodynamic stability of the ionization isomers 1·2H2O and cis/trans-2·2H2O, their molecular structures as well as the vibrational spectra and the energetics of the Cr(III)- Hhydia/hydia(-) were studied by means of density functional theory calculations and found to be in excellent agreement with our experimental observations.
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Controlling the Ring Curvature, Solution Assembly, and Reactivity of Gigantic Molybdenum Blue Wheels.
J. Am. Chem. Soc.
PUBLISHED: 09-29-2014
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We describe the synthesis, structure, self-assembly, solution chemistry, and mass spectrometry of two new gigantic decameric molybdenum blue wheels, {Mo200Ce12} (1) and {Mo100Ce6} (2), by building block rearrangement of the tetradecameric {Mo154} framework archetype and control of the architecture's curvature in solution from the addition of Ce(III). The assembly of 1 and 2 could be directed accordingly by adjusting the ionic strength and acidity of the reaction mixture. Alternatively, the dimeric cluster {Mo200Ce12} could be transformed directly to the monomeric species {Mo100Ce6} upon addition of a potassium salt. ESI-ion mobility mass spectra were successfully obtained for both {Mo200Ce12} and {Mo100Ce6}, which is the first report in molybdenum blue chemistry thereby confirming that the gigantic clusters are stable in solution and that ion mobility measurements can be used to characterize nanoscale inorganic molecules.
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Polyoxometalate based open-frameworks (POM-OFs).
Chem Soc Rev
PUBLISHED: 07-10-2014
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Polyoxometalate-based open frameworks (POM-OFs) are extended architectures incorporating metal-oxide cluster units and comprise an emergent family of materials with a large diversity of topologies, structural flexibility and functionality at the nanoscale. Not only do POM-OFs present a wide range of configurable structures, but also a have a vast array of physical properties which reflect the properties of the various 'modular' molecular inputs. Here we describe the methodologies that can be used to construct POM-OF materials with important catalytic, electronic, and structural properties and discuss the advantages compared to the metal organic framework analogues. We also show that it is possible to construct POM-OF materials and design and/or fine tune their functionality by manipulating the initially generated building block libraries as well as by controlling the self-assembly towards the specific intermediate (POM) species which is the chemical and structural "information" carrier of the targeted POM-OF material.
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Design and fabrication of memory devices based on nanoscale polyoxometalate clusters.
Nature
PUBLISHED: 06-26-2014
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Flash memory devices-that is, non-volatile computer storage media that can be electrically erased and reprogrammed-are vital for portable electronics, but the scaling down of metal-oxide-semiconductor (MOS) flash memory to sizes of below ten nanometres per data cell presents challenges. Molecules have been proposed to replace MOS flash memory, but they suffer from low electrical conductivity, high resistance, low device yield, and finite thermal stability, limiting their integration into current MOS technologies. Although great advances have been made in the pursuit of molecule-based flash memory, there are a number of significant barriers to the realization of devices using conventional MOS technologies. Here we show that core-shell polyoxometalate (POM) molecules can act as candidate storage nodes for MOS flash memory. Realistic, industry-standard device simulations validate our approach at the nanometre scale, where the device performance is determined mainly by the number of molecules in the storage media and not by their position. To exploit the nature of the core-shell POM clusters, we show, at both the molecular and device level, that embedding [(Se(iv)O3)2](4-) as an oxidizable dopant in the cluster core allows the oxidation of the molecule to a [Se(v)2O6](2-) moiety containing a {Se(v)-Se(v)} bond (where curly brackets indicate a moiety, not a molecule) and reveals a new 5+ oxidation state for selenium. This new oxidation state can be observed at the device level, resulting in a new type of memory, which we call 'write-once-erase'. Taken together, these results show that POMs have the potential to be used as a realistic nanoscale flash memory. Also, the configuration of the doped POM core may lead to new types of electrical behaviour. This work suggests a route to the practical integration of configurable molecules in MOS technologies as the lithographic scales approach the molecular limit.
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Molecular chalcoxides (chalcopolyoxometalates): a family of functional materials with emergent properties.
Chemistry
PUBLISHED: 05-07-2014
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Molecular chalcoxides (chalcoPOMs; POMs=polyoxometalates), a recently discovered new family of compounds with well-defined building block attributes, are discussed in terms of developing new functional materials. This is because the combination of sulfur-containing metallo-dimers with highly condensed metallo-oxo units allows the assembly of new clusters with hybrid properties intermediate between those of polyoxometalates and chalcogenides. Moreover, the prospect that the molecular chalcoxides could be excellent new models for a better understanding of chalcogenide's functionality, as well as promising candidates for the development of new functional molecule-based or composite nanomaterials, is proposed. The concepts that support my aim for further development of the new family of molecular chalcoxides as functional materials and my vision for their potential implications in the materials chemistry are discussed.
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Assembly and core transformation properties of two tetrahedral clusters: [Fe(III)13P8W60O227(OH)15(H2O)2]30- and [Fe(III)13P8W60O224(OH)12(PO4)4]33-.
Dalton Trans
PUBLISHED: 02-12-2014
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Two nanosized 2.6 nm Fe(III) substituted polyoxotungstates [Fe(III)13P8W60O227(OH)15(H2O)2](30-) (1) and [Fe(III)13P8W60O224(OH)12(PO4)4](33-) (2) are presented herein. Both clusters are synthesized from the reactions of trilacunary polyoxotungstate precursor [?-P2W15O56](12-) and FeCl3 under strict pH control at atmospheric pressure. The compounds are fully characterised in the solid state (FTIR and single-crystal XRD, elemental and thermogravimetric analyses), solution (cyclic voltammetry and UV-Vis spectroscopy) and in the gas phase (ESI-MS). An {Fe(III)13} core is present in both clusters which can be described as Archimedean solids (truncated tetrahedron, 1; elongated cuboctahedron, 2). 1 shows iron delivery properties coupled to a K(+)-triggered transformation of the {Fe13} core to a {K?Fe12} core in solution. Cyclic voltammetry shows the presence of independent W- and Fe-centred redox processes that support the stability of the clusters in solution. ESI-MS analyses confirm further the stability of 1 and 2 in the gas phase.
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Discovery of gigantic molecular nanostructures using a flow reaction array as a search engine.
Nat Commun
PUBLISHED: 01-01-2014
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The discovery of gigantic molecular nanostructures like coordination and polyoxometalate clusters is extremely time-consuming since a vast combinatorial space needs to be searched, and even a systematic and exhaustive exploration of the available synthetic parameters relies on a great deal of serendipity. Here we present a synthetic methodology that combines a flow reaction array and algorithmic control to give a chemical 'real-space' search engine leading to the discovery and isolation of a range of new molecular nanoclusters based on [Mo(2)O(2)S(2)](2+)-based building blocks with either fourfold (C4) or fivefold (C5) symmetry templates and linkers. This engine leads us to isolate six new nanoscale cluster compounds: 1, {Mo(10)(C5)}; 2, {Mo(14)(C4)4(C5)2}; 3, {Mo(60)(C4)10}; 4, {Mo(48)(C4)6}; 5, {Mo(34)(C4)4}; 6, {Mo(18)(C4)9}; in only 200 automated experiments from a parameter space spanning ~5 million possible combinations.
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A redox-triggered structural rearrangement in an iodate-templated polyoxotungstate cluster cage.
Chem. Commun. (Camb.)
PUBLISHED: 09-12-2013
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The new tungstatoiodate, ?-[H5W18O59(IO3)](6-), containing I(V)O3(-) within a {W18O54} metal oxide framework has been prepared and shown by X-ray crystallography and mass spectrometry to be derived from the fully oxidised [H3W18O56(IO6)](6-) by two-electron reduction accompanied by a redox-triggered structural rearrangement where three I-O covalent bonds are broken.
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Exploring the assembly of supramolecular polyoxometalate triangular morphologies with Johnson solid cores: [(Mn(II)(H2O)3)2(K?{?-GeW10Mn(II)2O38}3)]19-.
Inorg Chem
PUBLISHED: 07-26-2013
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A new polyoxometalate (POM) cluster compound is presented which incorporates a trimeric assembly of Keggin-type germanotungstate fragments trapping a Johnson-type solid {Mn8} core. The mixed K-Li salt of the polyanion [(Mn(II)(H2O)3)2(K?{?-GeW10Mn(II)2O38}3)](19-) was characterized in the solid state and solution. The correlation of the assembly processes and the observed architecture of the "trinity" family of POMs is discussed.
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Assembly of thiometalate-based {Mo16 } and {Mo36 } composite clusters combining [Mo2O2S2 ](2+) cations and selenite anions.
Adv. Mater. Weinheim
PUBLISHED: 06-05-2013
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A new family of thiometalate-based composite molecular materials is synthesized and characterized. 1.6 and 1.9 nm-sized clusters are observed in the gas phase utilizing high-resolution ESI-MS. The diversity of the selenite anions as an inorganic ligand is demonstrated by the isolation of the highest nuclearity selenium-based oxothiometalate materials reported so far. The observed proton conductivity of the selenite based oxothiometalate species renders them as promising alternative materials for fuel-cell applications.
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Connecting theory with experiment to understand the initial nucleation steps of heteropolyoxometalate clusters.
Phys Chem Chem Phys
PUBLISHED: 08-24-2011
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A complimentary combination of Density Functional Theory (DFT) methodology and Electrospray Ionization-Mass Spectrometry (ESI-MS) has been utilized to increase our limited understanding of the first nucleation steps in the formation of the [XM(12)O(40)](n-) Keggin polyoxometalates (POMs) (where addenda metal atom M = W or Mo, and the heteroatom X = P or As). We postulate that the first key steps of nucleation into discrete, high nuclearity heteropolyanions proceed via the formation of isodinuclear species (e.g. [M(2)O(7)](2-)), which undergo successive steps of protonation and water condensation to form a heterotrinuclear fragment, which acts as a template for the constituent parts required for subsequent aggregation and formation of the plenary Keggin heteropolyanion. The stability of calculated structures of the numerous postulated intermediates has been analysed and discussed in detail, and these results complemented using experimental mass spectrometry, using an assembly (reaction solution analysis) and disassembly (fragmentation of single crystals) approach. Overall, no significant differences between the Keggin POMs were found when changing the addenda metal atom (W or Mo) or the heteroatom (P or As); although small differences among the lowest-energy structures were detected.
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Exploring the structure and properties of transition metal templated {VM17(VO4)2} Dawson-like capsules.
Inorg Chem
PUBLISHED: 07-27-2011
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Vanadate(V)-templated Dawson-type capsules {V(IV)M(VI)(17)(VO(4))(2)} (M = Mo, W; 1-2) have been synthesized and investigated by electrochemical methods in aqueous and organic media using spectroscopic techniques, EPR, UV-vis/NIR, IR, and CSI-MS (cryospray ionization mass spec.), and the clusters have been examined in the solid state by magnetic studies. The collision-induced dissociation (CID-MS) studies confirmed the solution structures as well as helped pinpoint the position of the vanadium ion on the {VM(17)}-type shell, which was corroborated by EPR and theoretical studies.
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Combined theoretical and mass spectrometry study of the formation-fragmentation of small polyoxomolybdates.
Inorg Chem
PUBLISHED: 07-19-2011
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We investigate the assembly of small polyoxomolybdates using Car-Parrinello molecular dynamics simulations which show that there is an expansion of the coordination sphere of the Mo center from four to six in molybdate anions when the acidity of the solution is increased. With the help of complementary static density functional theory (DFT) calculations and electrospray ionization mass spectrometry experiments, we are able to postulate tentative mechanisms, with energy-cascade profiles, for the formation of the Lindqvist [Mo(6)O(19)](2-) anion. Similar to the family of isopolytungstates, it can be proposed that the [Mo(6)O(19)](2-) is formed by the aggregation of one molybdenum unit at a time; however, significant differences with respect to isopolytungstates are also found. The different behavior of chromates with respect to molybdates and tungstates is also considered.
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Assembly of a family of mixed metal {Mo:V} polyoxometalates templated by TeO3(2-): {Mo12V12Te3}, {Mo12V12Te2} and {Mo17V8Te}.
Chem. Commun. (Camb.)
PUBLISHED: 07-06-2011
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The influence of the pyramidal heteroanion, TeO(3)(2-) in the self-assembly of mixed metal (Mo/V) systems, is demonstrated by the isolation of three novel mixed-metal, mixed-valence architectures, {Mo(12)V(12)Te(3)} (1), {Mo(12)V(12)Te(2)} (2) and {Mo(17)V(8)Te} (3) with the tellurium centres exhibiting the novel ?(8)-TeO(4) and ?(9)-TeO(3) coordination modes while compounds 1 and 2 were discovered utilizing ESI mass spectrometry.
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A supramolecular heteropolyoxopalladate {Pd15} cluster host encapsulating a {Pd2} dinuclear guest: [Pd(II)2?{H7Pd(II)15O10(PO4)10}](9-).
J. Am. Chem. Soc.
PUBLISHED: 03-16-2011
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A high-nuclearity polyoxopalladate compound, [Pd(II)(2)?{H(7)Pd(II)(15)O(10)(PO(4))(10)}](9-) {Pd(II)(17)}, comprising a {Pd(15)} host occupied by a {Pd(2)} guest and the parent pristine "empty" [H(7)Pd(II)(15)O(10)(P(V)O(4))(10)](13-) {Pd(15)} cluster have both been prepared and characterized by single-crystal X-ray crystallography, (31)P NMR, CSI-MS, and XPS. The encapsulated {Pd(2)} has a short Pd(II)-Pd(II) distance within the {Pd(15)} host. Solution studies indicate that the empty host and filled guest complex are in equilibrium with each other, and UV titrations revealed a binding constant of ca. 10(3) for the guest Pd(II) ions, with a binding stoichiometry of almost 2.
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Design and synthesis of "dumb-bell" and "triangular" inorganic-organic hybrid nanopolyoxometalate clusters and their characterisation through ESI-MS analyses.
Chemistry
PUBLISHED: 01-24-2011
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A series of tris(hydroxymethyl)aminomethane (TRIS)-based linear (bis(TRIS)) and triangular (tris(TRIS)) ligands has been synthesised and were covalently attached to the Wells-Dawson type cluster [P(2)V(3)W(15)O(62)](9-) to generate a series of nanometer-sized inorganic-organic hybrid polyoxometalate clusters. These huge hybrids, with a molecular mass similar to that of small proteins in the range of ?10-16?kDa, were unambiguously characterised by using high-resolution ESI-MS. The ESI-MS spectra of these compounds revealed, in negative ion mode, a characteristic pattern showing distinct groups of peaks corresponding to different anionic charge states ranging from 3(-) to 8(-) for the hybrids. Each peak in these individual groups could be unambiguously assigned to the corresponding hybrid cluster anion with varying combinations of tetrabutylammonium (TBA) and other cations. This study therefore highlights the prowess of the high-resolution ESI-MS for the unambiguous characterisation of large, nanoscale, inorganic-organic hybrid clusters that have huge mass, of the order of 10-16?kDa. Also, the designed synthesis of these compounds points to the fact that we were able to achieve a great deal of structural pre-design in the synthesis of these inorganic-organic hybrid polyoxometalates (POMs) by means of a ligand design route, which is often not possible in traditional "one-pot" POM synthesis.
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Extended polyoxometalate framework solids: two Mn(II)-linked {P8W48} network arrays.
Inorg Chem
PUBLISHED: 11-30-2010
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Two polyoxometalate open framework (POMOF) materials have been synthesized using a secondary building unit (SBU) approach that facilitates the convergent assembly of multidimensional framework materials using a preassembled anionic SBU {P(8)W(48)}, with integrated "pore" 1 nm in diameter, and electrophilic manganese {Mn(2+)} linkers. This yields two new POMOFS with augmented hexagonal tiling (2 and 3), related to a known three-dimensional (3D) cubic array K(18)Li(6)[Mn(II)(8)(H(2)O)(48)P(8)W(48)O(184)]·108H(2)O (1), K(12)[Mn(II)(14)(H(2)O)(30)P(8)W(48)O(184)]·111H(2)O (2), and K(8)Li(4)[Mn(II)(14)(H(2)O)(26)P(8)W(48)O(184)]·105H(2)O (3). These frameworks have been crystallized from aqueous Li-buffered solutions of {P(8)W(48)} and Mn(II)(ClO(4))(2)·6H(2)O via careful control of the synthetic strategy akin to a crystal engineering approach using cation and temperature control to isolate different material architectures shown by compounds 1-3.
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Assembly of titanium embedded polyoxometalates with unprecedented structural features.
Dalton Trans
PUBLISHED: 11-05-2010
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Two titanium embedded polyoxometalates with unprecedented structural features are presented: a monotitanium containing tungstoantimonate Na(13)H(3)[TiO(SbW(9)O(33))(2)]·33 H(2)O featuring a {Ti=O}(2+) moiety (1) and a hexatitanium containing tungstoarsenate K(6)[Ti(4)(H(2)O)(10)(AsTiW(8)O(33))(2)]·30 H(2)O containing a {Ti(4)(H(2)O)(10)}(16+) moiety (2). Both compounds have been fully characterised by single crystal X-ray diffraction, elemental analysis, IR and TGA. 1 is constructed from two ?-B-{Sb(III)W(9)O(33)} fragments linked by five sodium cations and an unprecedented square pyramidal Ti(O)O(4) group with a terminal Ti=O bond, and 2 exhibits a Krebs-type structure composed of two {AsTiW(8)O(33)} fragments, where one W(VI) centre has been substituted for a Ti(IV) centre in each, fused together via a belt of four additional Ti(IV) centres. This system represents the tungsten Ti-incorporated polyoxoanion with one of the highest Ti:W ratios so far reported. Additionally, 2 could also be isolated as an n-tetrabutylammonium salt and has been further characterised by electrochemistry and electrospray ionisation (ESI) MS studies. Due to the unique nature of these systems, both have been fully investigated using DFT calculations yielding highly interesting results. Structure 1 has been optimised with five sodium atoms in the belt position, which in addition to reducing the high charge of the cluster influence a stabilisation of the antimony lone pairs. Electrostatic potential calculations highlight the high electronegativity of the terminal oxygen on the titanium centre, enhancing real potentiality as a reactive site for catalysis.
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Controlling transformations in the assembly of polyoxometalate clusters: {Mo11V7}, {Mo17V8} and {Mo72V30}.
Chem. Commun. (Camb.)
PUBLISHED: 10-08-2010
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The reaction of molybdate with vanadium(V) in the presence of sulfite anions is explored showing how, via cation control, stepwise assembly through the {Mo(11)V(7)} cluster yields a {M(25)} cluster-based compound, [Mo(VI)(11)V(V)(5)V(IV)(2)O(52)(?(9)-SO(3))(Mo(VI)(6)V(V)O(22))](10-) (1a), which was first discovered using cryospray mass spectrometry, whereas switching the cation away from ammonium allows the direct formation of the spherical Keplerate {Mo(72)V(30)} cluster.
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Self-assembly of a nanosized, saddle-shaped, solution-stable polyoxometalate anion built from pentagonal building blocks: [H34W119Se8Fe2O420]54-.
J. Am. Chem. Soc.
PUBLISHED: 08-06-2010
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Precise control of the "one-pot" reaction conditions is employed for the assembly of a nanosized 2.8 nm cluster, [H(34)W(119)Se(8)Fe(2)O(420)](54-) (1a), which is templated using eight selenite units and two iron(III) centers. Not only is this cluster characterized structurally using X-ray crystallography, it is the largest polyoxotungstate to be observed intact in solution using ESI-MS, with a molecular mass of ca. 30,000 Da.
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Understanding and mapping the assembly of a family of trimeric polyoxometalates: transition metal mediated Wells-Dawson (M18)-trimers.
Dalton Trans
PUBLISHED: 06-09-2010
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Four iso-structural triple Wells-Dawson-type phosphotungstate compounds incorporating six transition metal ion linkers are presented of the form [(M2P2W16O60)3](24-/30-), 1-4, where M = Co, Mn, Fe, Ni respectively and compounds 3 and 4 are revealed for the first time uniting a family of isostructural clusters. Further, a comparative study of the solid-state arrangements of polyoxoanions 1-4 is presented as well as an in-depth discussion of the synthetic conditions which give rise to the formation of the clusters. Each cluster subunit displays an unprecedented diequatorial substitution pattern facilitating the combination of three such units into a trimer, creating central cavities in the range 6.61-6.82 A. The solid state arrangements of polyoxoanions 1, 3 and 4 are similar, but as a result of the relevant synthetic approaches, they differ greatly from that of 2. Electrochemical analysis of the new structures is detailed revealing that polyoxoanion 4 shows potential as an electrocatalyst in the reduction of nitrites.
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Tri-, deca- and dodecanuclear Co(III)-pyrazolate metallacycles.
Chem. Commun. (Camb.)
PUBLISHED: 03-12-2010
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Reactions of a Co(III) salt with pyrazoles in the presence of a base have yielded metallacyclic {Co(3)}, {Co(10)} and {Co(12)} species whose structural characterization points to a parallel between analogous carboxylate and pyrazolate motifs.
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Face-directed self-assembly of an electronically active Archimedean polyoxometalate architecture.
Nat Chem
PUBLISHED: 01-29-2010
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The convergent assembly of metal-organic frameworks has enabled the design of porous materials using a structural building unit approach, but functional systems incorporating pre-assembled structural building unit pore openings are rare. Here, we show that the face-directed assembly of a ring-shaped macrocyclic polyoxometalate structural building unit, {P(8)W(48)O(184)}(40-) with an integrated 1-nm pore as an aperture synthon, with manganese linkers yields a vast three-dimensional extended framework architecture based on a truncated cuboctahedron. The 1-nm-diameter entrance pores of the {P(8)W(48)O(184)}(40-) structural building unit lead to approximately spherical 7.24-nm(3) cavities containing exchangeable alkali-metal cations that can be replaced by transition-metal ions through a cation exchange process. Control over this process can be exerted by either electrochemically switching the overall framework charge by manipulating the oxidation state of the manganese linker ions, or by physically gating the pores with large organic cations, thus demonstrating how metal-organic framework-like structures with integrated pores and new physical properties can be assembled.
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Cation controlled assembly and transformation of mono- and bi-sulfite templated dawson-type polyoxotungstates.
Inorg Chem
PUBLISHED: 01-22-2010
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The Dawson-like polyoxometalate clusters (TEAH)(6)[H(2)W(18)O(57)(SO(3))] (1) and (DMAH)(8)[W(18)O(56)(SO(3))(2)(H(2)O)(2)] (2) were synthesized under similar reaction conditions by employing triethanolammonium (TEAH(+)) and dimethylammonium (DMAH(+)) as cations, respectively. Crystallographic studies revealed that compound 1 has a compressed, peanut-like {W(18)} cage containing a single sufilte anion where each cage metal atom supports one terminal oxo-based ligand whereas compound 2 also has a {W(18)} cage, but four of the eighteen cage metal atoms support two terminal oxo-based ligands with two sulfite anions embedded in the cluster.
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Unveiling the transient template in the self-assembly of a molecular oxide nanowheel.
Science
PUBLISHED: 01-02-2010
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Self-assembly has proven a powerful means of preparing structurally intricate nanomaterials, but the mechanism is often masked by the common one-pot mixing procedure. We employed a flow system to study the steps underlying assembly of a previously characterized molybdenum oxide wheel 3.6 nanometers in diameter. We observed crystallization of an intermediate structure in which a central {Mo36} cluster appears to template the assembly of the surrounding {Mo150} wheel. The transient nature of the template is demonstrated by its ejection after the wheel is reduced to its final electronic state. The templates role in the self-assembly mechanism is further confirmed by the deliberate addition of the template to the reaction mixture, which greatly accelerates the assembly time of the {Mo150} wheel and increases the yield.
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The trinity of polyoxometalates: connecting {M12} Keggin and {M18} Dawson clusters to triangles.
Chem. Commun. (Camb.)
PUBLISHED: 04-16-2009
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Two topologically equivalent triangular POM aggregates based upon the Keggin () and Dawson () cluster species, with distinctive double {W-O-M} intra-molecular linkages involving Mn(III) and Co(III) ions are presented; both these compounds demonstrate electrocatalytic activity.
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Unravelling the complexities of inorganic and supramolecular self-assembly in solution with electrospray and cryospray mass spectrometry.
Chem. Commun. (Camb.)
PUBLISHED: 02-13-2009
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Electrospray (ESI) and cryospray mass spectrometry (CSI-MS) are proving to be exceptionally versatile tools when used in conjunction with high resolution time-of-flight (TOF) systems to investigate the self-assembly of supramolecular architectures, inorganic coordination and organometallic compounds, labile molecules and clusters both from a structural and mechanistic point of view. In this feature article, we review very recent progress where mass spectrometry is being applied to highly labile and complex coordination and polyoxometalate (POM) cluster systems and we present some highlights from our initial electrospray and cryospray studies, which probe the self-assembly of inorganic cluster architectures. We discuss the major contributions of ESI and CSI-MS to labile and self-assembling inorganic architectures with great emphasis on future potential and ramifications for inorganic chemistry and the area of self-assembly as a whole.
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A flow-system array for the discovery and scale up of inorganic clusters.
Nat Chem
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The batch synthesis of inorganic clusters can be both time consuming and limited by a lack of reproducibility. Flow-system approaches, now common in organic synthesis, have not been utilized widely for the synthesis of clusters. Herein we combine an automated flow process with multiple batch crystallizations for the screening and scale up of syntheses of polyoxometalates and manganese-based single-molecule magnets. Scale up of the synthesis of these architectures was achieved by programming a multiple-pump reactor system to vary reaction conditions sequentially, and thus explore a larger parameter space in a shorter time than conventionally possible. Also, the potential for using the array as a discovery tool is demonstrated. Successful conditions for product isolation were identified easily from the array of reactions, and a direct route to scale up was then immediately available simply by continuous application of these flow conditions. In all cases, large quantities of phase-pure material were obtained and the time taken for the discovery, repetition and scale up decreased.
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Controlling the self-assembly of a mixed-metal Mo/V-selenite family of polyoxometalates.
Chemistry
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Five mixed-metal mixed-valence Mo/V polyoxoanions, templated by the pyramidal SeO(3)(2-) heteroanion have been isolated: K(10)[Mo(VI)(12)V(V)(10)O(58)(SeO(3))(8)]?18 H(2)O (1), K(7)[Mo(VI)(11)V(V)(5)V(IV)(2)O(52)(SeO(3))]?31 H(2)O (2), (NH(4))(7)K(3)[Mo(VI)(11)V(V)(5)V(IV)(2)O(52)(SeO(3))(Mo(V)(6)V(V)-O(22))]?40 H(2)O (3), (NH(4))(19)K(3)[Mo(VI)(20)V(V)(12)V(IV)(4)O(99)(SeO(3))(10)]?36 H(2)O (4) and [Na(3)(H(2)O)(5){Mo(18-x)V(x)O(52)(SeO(3))} {Mo(9-y)V(y)O(24)(SeO(3))(4)}] (5). All five compounds were characterised by single-crystal X-ray structure analysis, TGA, UV/Vis and FT-IR spectroscopy, redox titrations, and elemental and flame atomic absorption spectroscopy (FAAS) analysis. X-ray studies revealed two novel coordination modes for the selenite anion in compounds 1 and 4 showing ?,? and ?,? coordination motifs. Compounds 1 and 2 were characterised in solution by using high-resolution ESI-MS. The ESI-MS spectra of these compounds revealed characteristic patterns showing distribution envelopes corresponding to 2- and 3- anionic charge states. Also, the isolation of these compounds shows that it may be possible to direct the self-assembly process of the mixed-metal systems by controlling the interplay between the cation "shrink-wrapping" effect, the non-conventional geometry of the selenite anion and fine adjustment of the experimental variables. Also a detailed IR spectroscopic analysis unveiled a simple way to identify the type of coordination mode of the selenite anions present in POM-based architectures.
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Engineering polyoxometalates with emergent properties.
Chem Soc Rev
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Polyoxometalates are clusters of metal-oxide units, comprising a large diversity of nanoscale structures, and have many common building blocks; in fact polyoxometalate clusters are perhaps the largest non-biologically derived molecules structurally characterised. Not only can polyoxometalates have gigantic nanoscale molecular structures, but they also a have a vast array of physical properties, many of which can be specifically engineered-in. Here we describe how building block libraries of polyoxometalates can be used to construct systems with important catalytic, electronic, and structural properties. We also show that it is possible to construct complex chemical systems based upon polyoxometalates, manipulating the templating/self templating rules to exhibit emergent processes from the molecular to the macroscopic scale.
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Organic-soluble lacunary {M2(P2W15)2} polyoxometalate sandwiches showing a previously unseen ???? isomerism.
Dalton Trans
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New polyoxometalate sandwiches have been formed where two [P(2)W(15)O(56)](12-) lacunary Dawson clusters encapsulate two transition metal ions to give clusters with the general formula [M(II)(2)(P(2)W(15)O(56))(2)](20-) (where M = Mn, Co, and Ni respectively), [Fe(III)(2)(P(2)W(15)O(56))(2)](18-), and [Cu(II)(4)(P(2)W(15)O(56))(2)](16-). The Mn, Co, and Ni clusters exhibit a hitherto unseen ???? isomeric geometry and all five compounds are associated with tetrabutylammonium cations which allow for their dissolution in non-aqueous solvent.
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Assembly and autochirogenesis of a chiral inorganic polythioanion Möbius strip via symmetry breaking.
J. Am. Chem. Soc.
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Using [Mo(2)S(2)O(2)(H(2)O)(6)](2+) and squarate dianion, we synthesized the thiometalate ring compounds [(Mo(2)S(2)O(2))(x)(OH)(y)(C(4)O(4))(z)(Mo(2)O(8))(o)(H(2)O)(p)](n-), where [x,y,z,o,p,n] = [7,14,2,0,2,4] for 1, [6,8,2,2,4,8] for 2, and [4,6,1,1,0,4] for both 3a and 3b, which are chiral and nonchiral isomers, respectively. Not only do the four thiometalate clusters show decreasing symmetry at the molecular level across the series, but the incorporation of the "addendum" {Mo(2)O(8)}(o) unit also allows the thiometalate ring to twist. The reaction initially yields the chiral molecule 3a with a twisted ring, which undergoes spontaneous resolution upon crystallization; the reaction mixture later yields the intrinsically nonchiral isomer 3b with a nontwisted ring. In addition, the compounds are able to promote the electrocatalytic evolution of hydrogen.
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Correlating the magic numbers of inorganic nanomolecular assemblies with a {Pd84} molecular-ring Rosetta Stone.
Proc. Natl. Acad. Sci. U.S.A.
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Molecular self-assembly has often been suggested as the ultimate route for the bottom-up construction of building blocks atom-by-atom for functional nanotechnology, yet structural design or prediction of nanomolecular assemblies is still far from reach. Whereas nature uses complex machinery such as the ribosome, chemists use painstakingly engineered step-by-step approaches to build complex molecules but the size and complexity of such molecules, not to mention the accessible yields, can be limited. Herein we present the discovery of a palladium oxometalate {Pd(84)}-ring cluster 3.3 nm in diameter; [Pd(84)O(42)(OAc)(28)(PO(4))(42)](70-) ({Pd(84)} ? {Pd(12)}(7)) that is formed in water just by mixing two reagents at room temperature, giving crystals of the compound in just a few days. The structure of the {Pd(84)}-ring has sevenfold symmetry, comprises 196 building blocks, and we also show, using mass spectrometry, that a large library of other related nanostructures is present in solution. Finally, by analysis of the symmetry and the building block library that construct the {Pd(84)} we show that the correlation of the symmetry, subunit number, and overall cluster nuclearity can be used as a "Rosetta Stone" to rationalize the "magic numbers" defining a number of other systems. This is because the discovery of {Pd(84)} allows the relationship between seemingly unrelated families of molecular inorganic nanosystems to be decoded from the overall cluster magic-number nuclearity, to the symmetry and building blocks that define such structures allowing the prediction of other members of these nanocluster families.
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Cation induced structural transformation and mass spectrometric observation of the missing dodecavanadomanganate(IV).
Dalton Trans
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The heteropolyvanadate cluster [(n-C(4)H(9))(4)N](4)[Mn(IV)V(12)O(34)]·2CH(3)CN has been isolated by cation exchange from K(10)[(Mn(IV)V(11)O(32))(2)]·20H(2)O. The structural transformation has been confirmed by X-ray single crystal structure determination and cryospray ionization mass spectrometry measurements.
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Oscillatory template exchange in polyoxometalate capsules: a ligand-triggered, redox-powered, chemically damped oscillation.
J. Am. Chem. Soc.
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The redox-controlled driven oscillatory template exchange between phosphate (P) and vanadate (V) anions enclosed in an {X(2)M(18)} cluster is reported. Extensive investigations using a range of techniques, including correlated ESI-MS, EPR, and UV-vis as a function of reaction time, showed that six complete oscillations interconverting the capsule species present in solution from {P(2)M(18)} to {V(2)M(18)} were possible, provided that a sufficient concentration of the TEA reducing agent was present in solution.
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Solution-phase monitoring of the structural evolution of a Molybdenum Blue nanoring.
J. Am. Chem. Soc.
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The inorganic host-guest complex Na(22){[Mo(VI)(36)O(112)(H(2)O)(16)]?[Mo(VI)(130)Mo(V)(20)O(442)(OH)(10)(H(2)O)(61)]}·180H(2)O ? {Mo(36)}?{Mo(150)}, compound 1, has been isolated in its solid crystalline state via unconventional synthesis in a custom flow reactor. Carrying out the reaction under controlled flow conditions selected for the generation of {Mo(36)}?{Mo(150)} as the major product, allowing it to be reproducibly isolated in a moderate yield, as opposed to traditional "one-pot" batch syntheses that typically lead to crystallization of the {Mo(36)} and {Mo(150)} species separately. Structural and spectroscopic studies of compound 1 and the archetypal Molybdenum Blue (MB) wheel, {Mo(150)}, identified compound 1 as a likely intermediate in the {Mo(36)} templated synthesis of MB wheels. Further evidence illustrating the template effect of {Mo(36)} to MB wheel synthesis was indicated by an increase in the yield and rate of production of {Mo(150)} as a direct result of the addition of preformed {Mo(36)} to the reaction mixture. Dynamic light scattering (DLS) techniques were also used to corroborate the mechanism of formation of the MB wheels through observation of the individual cluster species in solution. DLS measurement of the reaction solutions from which {Mo(36)} and {Mo(150)} crystallized gave particle size distribution curves averaging 1.9 and 3.9 nm, consistent with the dimensions of the discrete clusters, which allowed the use of size as a possible distinguishing feature of these key species in the reduced acidified molybdate solutions and to observe the templation of the MB wheel by {Mo(36)} directly.
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