Polyoxometalate chemistry from topology via self assembly to applications (2001)

Polyoxometalate Chemistry From Topology via Self-Assembly to Applications Edited by Michael T Pope Georgetown University, Washington, DC, U.S.A and Achim Müller University of Bielefeld, Bielefeld, Germany KLUWER ACADEMIC PUBLISHERS NEW YORK, BOSTON, DORDRECHT, LONDON, MOSCOW eBook ISBN: Print ISBN: 0-306-47625-8 0-7923-7011-2 ©2002 Kluwer Academic Publishers New York, Boston, Dordrecht, London, Moscow Print ©2001 Kluwer Academic Publishers All rights reserved No part of this eBook may be reproduced or transmitted in any form or by any means, electronic, mechanical, recording, or otherwise, without written consent from the Publisher Created in the United States of America Visit Kluwer Online at: and Kluwer's eBookstore at: http://kluweronline.com http://ebooks.kluweronline.com Contents Introduction to Polyoxometalate Chemistry: from Topology via Self-Assembly to Applications Synthetic Strategies Rational Approaches to Polyoxometalate Synthesis Functionalization of Polyoxometalates: Achievements and Perspectives 23 From the First Sulfurated Keggin Anion to a New Class of Compounds Based on the [M2O2S2]2+ Building Block M = M0,W 39 Organometallic Oxometal Clusters 55 Structures: Molecular and Electronic Spherical (Icosahedral) Objects in Nature and Deliberately Constructable Molecular Keplerates: Structural and Topological Aspects 69 Syntheses and Crystal Structure Studies of Novel Seleniumand Tellurium-Substituted Lacunary Polyoxometalates 89 Vibrational Spectroscopy of Heteropoly Acids 101 Bond-Stretch Isomerism in Polyoxometalates? 117 Quantum-Chemical Studies of Electron Transfer in TransitionMetal Substituted Polyoxometalates 135 Solution Equilibria and Dynamics 10 Aqueous Peroxoisopolyoxometalates 145 11 Molybdate Speciation in Systems Related to the Bleaching of Kraft Pulp 161 12 NMR Studies of Various Ligands Coordinated to Paramagnetic Polyoxometalates 175 This page has been reformatted by Knovel to provide easier navigation v vi Contents From Discrete Clusters to Networks and Materials 13 Molecular Aspect of Energy Transfer from Tb3+ to Eu3+ in the Polyoxometalate Lattices: an Approach for Molecular Design of Rare-Earth Metal-Oxide Phosphors 187 14 Conducting and Magnetic Organic/Inorganic Molecular Materials Based on Polyoxometalates 205 15 Molecular Materials from Polyoxometalates 231 16 Framework Materials Composed of Transition Metal Oxide Clusters 255 17 Perspectives in the Solid State Coordination Chemistry of the Molybdenum Oxides 269 18 Polyoxometalate Clusters in a Supramolecular Self-Organized Environment: Steps towards Functional Nanodevices and Thin Film Applications 301 19 Polyoxometalate Chemistry: a Source for Unusual Spin Topologies 319 20 Heteropolyanions: Molecular Building Blocks for Ultrathin Oxide Films 329 Applications: Catalysis, Biological Systems, Environmental Studies 21 Selective Oxidation of Hydrocarbons with Hydrogen Peroxide Catalyzed by Iron-Substituted Silicotungstates 335 22 Aerobic Oxidations Catalyzed by Polyoxometalates 347 23 Polyoxoanions in Catalysis: from Record Catalytic Lifetime Nanocluster Catalysis to Record Catalytic Lifetime Catechol Dioxygenase Catalysis 363 24 Ribosomal Crystallography and Heteropolytungstates 391 25 Photocatalytic Decontamination by Polyoxometalates 417 Index 425 This page has been reformatted by Knovel to provide easier navigation Introduction to Polyoxometalate Chemistry : From Topology via SelfAssembly to Applications M T POPE Department of Chemistry, Georgetown University, Washington DC 20057, USA A MÜLLER Department of Chemistry, University of Bielefeld, D-33501 Bielefeld, Germany The high abundance of oxygen (55 atom %) in the Earth’s Crust can only be partly attributable to the oceans, the silicate-based rocks, and clays Even when and are excluded from the accounting, oxygen is still dominant at 47 atom % Clearly, the chemistry of combined oxygen is an important component of our environment The bulk of this chemistry is either aqueous solution chemistry of oxoanions of the nonmetals, or the solid-state and surface chemistry of insoluble metal oxides However, although it is only a very small fraction of the natural environment, there exists a third aspect of oxygen chemistry, that of the polyoxometalates, which spans both solution and “metal oxide” realms As amply demonstrated by the contributions to the present book, this chemistry offers opportunities, insights, properties, and applications that cannot be matched by any other single group of compounds Polyoxometalates are the polyoxoanions of the early transition elements, especially vanadium, molybdenum, and tungsten Although they have been investigated since the last third of the 19th century, it is only within the last four or five decades that modern experimental techniques have begun to reveal the range of structure and reactivity of these substances Fundamental questions regarding the limits to composition, size and structure, metal incorporation, mechanisms of synthesis and reactivity, remain essentially unanswered at present In spite of much research activity concerning practical applications of polyoxometalates, especially in heterogeneous and homogeneous catalysis, and in medicine (antiviral and antitumoral agents), it is certainly fair to say, considering the several thousand known polyoxometalates and their derivatives, that their potential in these and other areas remains poorly developed In the following chapters current research in several aspects of polyoxometalate chemistry is summarized by some of the leading workers in this field who participated in a workshop held at the Center for Interdisciplinary Research (ZiF) of the University of Bielefeld in October 1999 Two kinds of polyoxoanions are known, those exemplified by the silicates, and oxoanions of neighboring main-group elements, and those of the early transition elements of groups and (Figure 1) Although both types of polyanions are constructed of linked polyhedra polyoxometalates are predominantly characterized by octahedra with short “terminal” bonds that tend to result in “closed” discrete structures with such bonds directed outwards In contrast, the main-group elements, especially M.T Pope and A Müller (eds.), Polyoxometalate Chemistry, 1–6 © 2001 Kluwer Academic Publishers Printed in the Netherlands phosphates and silicates, exhibit open (cyclic) or polymeric structures based on linked tetrahedra Figure Polyoxoanion-forming elements That polyoxometalates have an extensive solution chemistry in both aqueous and nonaqueous solvents is a consequence of low surface charge densities resulting in weak anion-cation attractions (lattice energies) relative to cation solvation energies In general, polyoxometalate anion surfaces contain both terminal and bridging oxygen atoms, and although there have been arguments to the contrary,1 all experimental evidence and recent density functional calculations2 are in agreement that the bridging oxygens carry a greater negative charge and are protonated in preference to terminal oxygens The latter atoms may be viewed as part of or groups in the case of polyoxometalates constructed of octahedra The existence of so-called “antiLipscomb” polyoxometalate structures in which an octahedron has three terminal oxygens (always in a facial arrangement) has been demonstrated only very rarely.3 In these cases protonation of one of the oxygens readily occurs, converting to with two cis terminal oxygens The formation of polyoxometalates, and especially the rational directed synthesis of specific structures presents a major challenge, but with enormous potential benefits Some different synthetic strategies in polyoxometalate chemistry are described in the first six chapters of this book These include processes in both aqueous and nonaqueous solvents, the incorporation of organic and organometallic functionalities, and the synthesis of polyoxothiometalates The recognition and characterization of extremely large polyoxometalates is a relatively recent development One of the most challenging problems in contemporary chemistry is the deliberate and especially synthon-based synthesis of multifunctional compounds and materials – including those with network structures – with desirable or predictable properties, such as mesoporosity (well-defined cavities and channels), electronic and ionic transport, ferro- as well as ferrimagnetism, luminescence, and catalytic activity Transition metal oxide-based compounds are of special interest in that respect For example, the deeply colored, mixed-valence hydrogen molybdenum bronzes – with their unusual property of high conductivity and wide range of composition play an important role in technology, industrial chemical processes, and materials science Their fields of applications range from electrochemical elements, hydrogenation and dehydrogenation catalysts, superconductors, passive electrochromic display devices, to "smart" windows The synthesis of such compounds or solids from preorganized linkable building blocks (synthons) with well-defined geometries and well-defined chemical properties is therefore of special interest to this end Interestingly, reduced polyoxomolybdates can serve as models for the hydrogen bronzes In generating large complex molecular systems we have to realize that natural processes are effected by the linking (directed as well as non-directed) of a huge variety of basic and welldefined fragments An impressive example of this, discussed in virtually all textbooks on biochemistry, is the self-aggregation process of the tobacco mosaic virus, which is based on preorganized units This process more or less meets the strategy in controlling the linking of fragments to form larger units and linking the latter again In the case of metal-oxide based clusters this means for instance that relatively large molecular fragments can principally be functionalized with groups which allow linking through characteristic reactions: For example, as mentioned above, protonation of highly reactive "anti-Lipscomb" groups positioned on polyoxometalate cluster fragments generates a terminal OH group and results in condensation reactions of the fragment via formation.3(b) The same principle basically applies also to lacunary polyoxotungstates that can be linked by transition metal, lanthanide, and actinide ions to form discrete watersoluble heteropolytungstate anions such as and or recrystallizable linear polymeric arrays (Figure 2) Figure Structures of and (Reference 4) In the generation of large polyoxometalate clusters, the concept of preorganized units is of particular importance due to the fact that the structural chemistry is often governed by differently transferable building units For example, the linking of polyoxometalate building blocks containing 17 molybdenum atoms ( units) results in the formation of cluster anions consisting of two or three of these units The following basic strategy, which is archetypical for polyoxometalate chemistry, is used for describing or analyzing a solid-state structure One decomposes, at least mentally, the objects into elementary building blocks (e.g., polygons, polyhedra or aggregates of these) and then tries to identify and explore the local matching rules according to which the building blocks are to be assembled to yield the objects considered Nanosized polyoxomolybdate clusters now also provide model objects for studies on the initial nucleation steps of crystallization processes, an interesting aspect for solid-state chemists and physicists as the initial steps for crystal growth are not known This is due to the fact that they represent well-defined molecular systems and have flexible (multi-dimensional) boundary conditions, i.e clusters with circular and spherical topologies can be considered as potential precursors for such growth It is envisaged that, with such an approach, it will be possible to unveil some of the mysteries associated with the biomineralization of structures such as the unicellular diatoms In the context of biomineralization, which takes place at room temperature (whilst chemists need high temperatures), it is remarkable that the linking of 'Giant-Spherical' clusters, described in Chapter 1, to a well-defined solid-state layer structure is also possible at room temperature Interestingly, even Keggin-type ions can be encapsulated in such cluster shells (Figure 3) In summary it is important in this context that (1) the above-mentioned nanostructured building blocks can even be isolated (according to their stability) and (2) they have nanostructured cavities and well-defined properties, thus offering the possibility to construct materials with desired emergent properties using characteristic synthons, in accordance with the rule, the whole (due to cooperativity) is more than the sum of the parts It is a short conceptual step from large polyoxometalates to metal-oxide-based materials Eight chapters (13 - 20) demonstrate the intensity of current research activity that focuses on the formation of new materials and on the solid state optical, electrical and magnetic properties of polyoxometalates In addition to the promise of polyoxometalate chemistry towards an understanding of selfassembly processes for inorganic materials with desired properties, much current research activity is also directed towards the incorporation or attachment of organic and organometallic groups.6 Several obvious advantages accrue from the availability of such derivatized polyoxometalates These include the ability to use established procedures of organic chemistry to assemble large polyanion arrays, to incorporate polyoxometalates into polymer matrices (see for example recent reports of hybrid polymer-based materials 7), to develop new polyoxometalate catalysts, and to form new, highly specific electron-dense labels, and phasing agents for X-ray crystallographic analysis of large biopolymers As Figure The route to a novel type of supramolecular compound: a layer structure built up by composites containing cluster shells and non-covalently encapsulated Keggin ions (A Müller et al., Angew Chem.Int.Ed.Engl 34, 3413 (2000)) shown in Chapter 24, even non-functionalized polyoxometalates can provide additional unexpected benefits for analysis of the structure of the ribosome Undoubtedly, at present, the most important and promising application of polyoxometalates lies in catalysis, both homogeneous and heterogeneous.8 Four chapters (21- 23, 25) summarize some recent activity in homogeneous catalysis, and Chapters - describe recent work on the fundamental solution chemistry and spectroscopic properties of polyoxometalates that underlie their catalytic behavior Driven by environmental concerns, green chemistry becomes a greater imperative for the chemical and pharmaceutical industries, and the demand for more selective and more robust catalysts, especially those that can be employed in aqueous environments is certain to increase The enormous versatility and variety of polyoxometalates offers considerable opportunities in this and in other areas.9 Acknowledgment We thank the ZiF authorities and the Volkswagen Foundation for generous financial support of the Workshop Research support from the National Science Foundation and the U.S Department of Energy (MTP) and from the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie (AM) is also gratefully acknowledged References K.H Tytko, J Mehmke, and S Fischer, Struct Bonding (Berlin) 93, 129-321 (1999) B.B Bardin, S.V Bordawekar, M Neurock, and R.J Davis, J Phys Chem B 102, 10817 (1998) (a) L Ma, S Liu, and J Zubieta, Inorg Chem 28, 175 (1989); (b) A Müller, E Krickemeyer, S Dillinger, J Meyer, H Bögge, and A Stammler, Angew Chem Int Ed Engl 35, 171 (1996); (c) R Klein and B Krebs, in Polyoxometalates: from Platonic Solids to Anti-Retroviral Activity, M.T Pope and A Müller, eds.; Kluwer, Dordrecht (1994), p 41 (a) K Wassermann, M.H Dickman, and M.T Pope, Angew Chem Int Ed Engl., 36, 1445 (1997); (b) M.T Pope, X Wei, K Wassermann, and M.H Dickman, C.R.Acad.Sci.Paris, 1, Ser IIc, 297 (1998); (c) M Sadakane, M.H Dickman, and M.T Pope, Angew Chem Int Ed Engl 39, 2914 (2000) (a) A Müller, P Kögerler, and H Bögge, Struct Bonding (Berlin) 96, 203 (2000); (b) A Müller, P Kögerler, and C Kuhlmann, J Chem Soc., Chem Commun 1347 (1999); (c) A Müller and C Serain, Acc Chem Res 33, (2000) P Gouzerh and A Proust, Chem Rev 98, 77 (1998) (a) C.R Mayer, V Cabuil, T Lalot, and R Thouvenot, Angew Chem Int Ed Engl 38, 3672 (1999); (b) C.R Mayer, R Thouvenot, and T Lalot, Chem Mater 12, 257 (2000) (a) J Mol Catal., A (special issue, C.L Hill, ed.) 114, - 371 (1996); (b) T Okuhara, N Mizuno, and M Misono, Adv Catal 41, 113 (1996); (c) R Neumann, Prog Inorg Chem 47, 317 (1998); (d) I V Kozhevnikov, Chem Rev 98, 171 (1998); (e) N Mizuno and M Misono, Chem Rev 98, 199 (1998); (f) M Sadakane and E Steckhan, Chem Rev 98, 219 (1998) D Katsoulis, Chem Rev 98, 359 (1998) 418 and through reductive activation may or may not participate further in the process, depending on the substrate This paper gives an overall account on the mineralization of a variety of diversified organic pollutants with UV and near visible light, in presence of representative POM, It also reports on the intermediates involved, as identified by HPLC-DAD, GC-MS and suggests the possible mechanistic route of the photocatalytic degradation process Experimental Aqueous solutions of various organic substrates (chloroacetic acid, lindane, cresol, phenol, chlorophenols and polychlorinated phenols), in presence of the catalyst were made by dissolving certain quantities of substrate in 0.1M Samples of 4.0 ml of the above solutions were added to a spectrophotometer cell (1-cm path), with total volume of about ml After 20 minutes of deaeration or oxygenation the cell was covered with an airtight serum cap Photolysis experiments were performed with an Oriel 1000 W Xe arc lamp, at 20° C, equipped with a cool water circulating filter to absorb the near IR radiation and 320, 345 nm filters to avoid possible direct photolysis of the organic substrates The incident radiation was reduced to about 40% with a slit diaphragm, in order to obtain reasonable photolysis times The solution was magnetically stirred throughout the experiment For experiments at higher pH, was used Limited work was done with which is unstable in aqueous solutions A Waters apparatus equipped with a PDA detector carried out HPLC analysis, for the determination of intermediates produced during photolysis GC analysis, for the determination of lindane, was carried out by a Varian Model 3400 gas chromatograph equipped with ECD, split/splitless injection port and a DB-1 fused silica capillary column GC analysis, for the determination of was carried using TCD and a m Porapack Q column Carbon dioxide content was calculated using a calibration curve, made of known quantities of and processed under the same experimental conditions Identification of intermediates was performed using a Micromass Platform II quadrupole mass spectrometer, equipped with a DB-5 fused silica capillary column The formation of maleic, oxalic, ethanoic and formic acids were analysed by suppressed ion chromatography, performed with a Dionex apparatus In order to have adequate quantities for the identification of intermediates by GC-MS, samples of 30 ml of the 2,4,6-TCP, were photolysed under the same conditions The photolysed solution was extracted with dichloromethane The organic layers were combined, dried through sodium sulfate and evaporated to Chloride ions were analysed spectrophotometrically [11] The degree of reduction of POMs in photolyzed deaerated solutions was calculated from the known extinction coefficients of the blue products and for the one- and two-electron reduction products, respectively.)[12] 419 Results and Discussion The excited state of POM arising from absorption of light at the band (near visible and UV light) is a powerful oxidizing reagent The oxidizing ability is manifested, mainly, through formation of OH radicals arising from the reaction of the excited POM with adsorbed water The existing prevailing mechanism of H-abstraction as the initial reaction of excited POM with organic substrates (mainly alcohols) has been modified by addition of one more step that involves the formation of OH radicals [10] This radical, as is well known, reacts with organic substrates, mainly alcohols, by Habstraction The formation of OH radicals, and the high oxidizing ability of the excited POM is responsible for the mineralization, i.e formation of and inorganic anions of a great variety of organic compounds and for that matter organic pollutants Several experimental approaches have suggested the formation of OH radicals: a) The detection of hydroxylation intermediates [5,6, 16], b) ESR data [13], c) The fact that the excited state potentials of, practically, all POM are more positive than the reaction and d) results concerning photodegradation of p-nitrosodimethylaniline, a known trapping reagent for OH radicals [14, 15] Following the first results on the subject [4], several other publications provided data on the mineralization of a great variety of organic pollutants with POM, such as phenols [6], chlorinated [5] and polychlorinated phenols [16], cresols [6], chloracetic acids [17], organochlorine incecticides (lindane, aldrin, endosulfan, DDT) [18, 19], heavily chlorinated compounds (HCB) [16] and herbicides(atrazine) [20] A typical experiment showing the effect of POM in the photodegradation of organic pollutants is presented in Fig Figure Photodecomposition of aqueous solutions of oxygenated solution 345 nm cut off filter, no catalyst; oxygenated solution, 320 nm cut off filter, no catalyst In presence of catalyst, with 320 nm cut off filter: Deoxygenated solution, oxygenated solution 420 As model compound 2,4 Dichlorophenol (2,4DCP) has been chosen It can be seen that the presence of catalyst can seriously accelerate the photodegradation process In the presence of dioxygen, more effective photocatalytic degradation of substrate takes place Dioxygen’s main function is the regeneration of the catalyst [21], participating in some cases in the initial decomposition of the substrates [6] No reaction takes place between POM and 2,4 DCP in the dark Fig indicates the decay of 2,4DCP and the gradual formation of and The mineralization proceeds via formation and decay of intermediates resulting from H-abstraction, hydroxylation and dehalogenation The formation and decay several of them are presented in Fig Figure Formation of presence of and decay of substrate upon photolysis of aqueous oxygenated solution in [16] 421 Figure Formation and decay of several intermediates upon photolysis of aqueous oxygenated solution of 2,4 DCP in presence of catalyst [16] The breaking of the aromatic ring is followed by the formation of various saturated and unsaturated aliphatic acids In all studies, so far, ethanoic acid has been detected The overall reactions involved are: Direct reaction of POM* with substrate Indirect reaction of POM with substrate, through OH radicals hydrogen abstraction, hydroxylation, dehalogenation, breaking of the aromatic ring, aliphatic acids; ( final products: and inorganic anions ) (5) 422 The key step in the photodecomposition of organic pollutants is the high affinity of organic substrates to POM It is this association that enables the reaction of the excited POM with traces (ppm or ppb level) of organic substrates to compete with the deactivation process that takes place within nanoseconds Detailed studies of formation and decay of the intermediates involved in the photodegradation of 2,4DCP have led to the following scheme: Scheme 1: Detected intermediates during photocatalytic degradation of 2,4DCP with POM [16] Other pollutants, whose solubility is limited to ppb values, undergo effective mineralization in presence of POM, as has been stated earlier Two typical cases are lindane and HCB whose photodecay is depicted in Figures and together with the formation of and The overall behavior of POM, as far as photodecomposition of organic pollutants is concerned, is reminiscent of the widely publicized For instance: (a) The final products in both cases are and inorganic anions 423 (b)Both methods proceed to mineralization via similar intermediates arising from Habstraction, hydroxylation and to a lesser extent dehalogenation However, the detail pathways to mineralization may present differences (c) The initial photodecomposition of organic pollutants by POM and follows first order kinetics Figure Formation of presence of and decay of substrate upon photolysis of aqueous oxygenated solution in Lindane, [16] Figure Formation of presence of [16] and decay of substrate upon photolysis of aqueous oxygenated solution in partially dissolved, 424 (d) The formation of and groups from aromatic carbons (i.e -CH groups) implies that in photocatalytic processes by POM, like in the case of there is a reductive (hydrogenation) pathway, going along the oxidation processes (e) Another important aspect as far as similarity of these two processes is concerned, is the decomposition of nitrogen containing aromatic rings In particular, atrazine photodecomposes within a few minutes by both methods, to cyanuric acid Cyanuric acid, on the other hand, resists photodegradation for hours either in presence of or POM Acknowledgements We thank the Ministry for Development, General Secretariat of Research and Technology for financing part of this work References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] O Legrini, E Oliveros, and A.M Brown, Chem Rev 93, 671 (1993), M.R Hoffmann, S.T Martin, W Choi and D Bahnemann, Chem Rev.,95, 69 (1995) P.V Kamat, Chem Rev., 93, 267 (1993) A Mylonas and E Papaconstantinou, J Mol Catal., 92, 261.( 1994) A Mylonas and E Papaconstantinou, J Photochem Photobiol A: Chem., 94, 77 (1996) A Mylonas E Papaconstantinou and V Roussis, Polyhedron, 15, 3211 (1996) E Papaconstantinou, A Argitis, D Dimotikali, A Hiskia and A Ioannidis, in Homogeneous and Heterogeneous Photocatalysis, (Eds E Pelizzetti, N Serpone), D Reidel Publ Co., Dordrecht 1986, p 415 E Papaconstantinou, Chem Soc Rev., 18, (1989) H Einaga and M Misono, Bull Chem Soc Jpn., 69, 3435 (1996) A Mylonas, A Hiskia, E Androulaki, D Dimotikali, E Papaconstantinou, Phys Chem Chem Phys., 1, 437 (1999) T M Florence, Anal Chim Acta, 54, 373 (1971) G.M Varga, E Papaconstantinou and M.T Pope, Inorg Chem., 9, 662 (1970) T Yamase, Inorg Chim Acta, , 76, L25 (1983) I Kraljik and C.N Trumbore, J.Am.Chem.Soc., , 87, 2547.( 1965) M Hatada, I Kraljik, A El Samahy and C.N Trumbore, J Phys Chem., 78, 888 (1974) A Hiskia, E Androulaki, A Mylonas, S Boyatzis, D Dimoticali, C Minero, E Pelizzetti and E Papaconstantinou, Res Chem Intermed., 1999, in press A Mylonas, A Hiskia, E Papaconstantinou, J Mol Catal., 114, 191 (1996) A Hiskia, A Mylonas D Tsipi and E Papaconstantinou, Pestic Sci., , 50, 171 (1997) A Hiskia, A Mylonas E Androulaki, D Dimotikali, D Tsipi and E Papaconstantinou, 5th Symp On Environmental Science and Technology, Lesbos, 1997, Vol.A, 309 A Hiskia, A Kokorakis, H Hennig and E Papaconstantinou, Book of Abstracts, 12th International Conference on Photochemical Conversion and Storage of Solar Energy, Berlin, Germany 3, W77.(1998) A Hiskia and E Papaconstantinou, Inorg Chem., 31, 163 (1992) Index Index terms Links A "anti-Lipscomb" structures ab initio calculations acceptor, inorganic activation of surface oxygen atoms 33 205 23 Advanced Oxidation Processes (AOP) 417 alkanes and alkenes 335 alkoxides amino acids 181 Anderson-Evans anion 220 anion ESI-MS 156 antimony 180 Archimedean solids (η -arene)Ru 2+ 69 63 B BEDT-TTF (bis(ethylenedithio)-tetrathiafulvalene) 208 bond-stretch isomerism 117 bromination 242 20 C catalysis, catechol dioxygenase 373 hydrogenation 363 oxidation 347 oxygenation 376 This page has been reformatted by Knovel to provide easier navigation 425 426 Index terms Links catalysts, approaches to polyoxoanion-based 376 autocatalytic catalyst evolution mechanisms 376 nanocluster-based 367 clusters 69 conformations 175 corrosion 329 Cp*(η -pentamethylcyclopentadienyl)Rh 2+ 62 cyclic cluster 45 η5-cyclopentadienyl derivatives 23 D decontamination DFT (density functional theory) dioxygenase 417 121 135 347 discrete geometry 69 discrete mathematics 69 distortional isomerism 117 DODA (dimethyldioctadecylammonium) 249 donor, organic 205 307 E electrical conductivity 205 246 electron transfer 139 347 electronic effects 23 electron microscopy (see TEM) electronic structure 117 equilibria 161 ESR spectra 244 ET, see BEDT-TTF etching 329 europium 187 135 247 This page has been reformatted by Knovel to provide easier navigation 351 427 Index terms EXAFS Links 31 F Forster-Dexter-type energy transfer 196 framework solids 255 functionalization 23 H Hammett Constant 13 heteropoly acid 101 heteropolyanions 329 hexametalates homogeneous and heterogeneous catalysis 363 hydrated proton 101 hydrogen bonding 103 hydrogen peroxide 335 hydrolytic aggregation hydrothermal synthesis 50 208 180 269 I inelastic neutron scattering 238 ion exchange 264 iron-substituted silicotungstates 335 isomers, bond stretch 117 distortional 117 linkage 180 octamolybdate 280 molybdovanadophosphate 351 isomorphous replacement 391 This page has been reformatted by Knovel to provide easier navigation 428 Index terms Links K kagome lattice 324 Keggin ion 329 Keggin oxothio polyanions 117 keplerates 69 kinetic and mechanistic studies 349 320 363 L Langmuir films 301 Langmuir-Blodgett films 231 lanthanides 187 large domain size 329 311 Lindqvist anions, see hexametalates linkage isomers 180 long-range order 329 M magic numbers 69 magnetic clusters 231 319 magnetic exchange 231 319 magnetic properties 205 manganese 55 mass spectrometry, electrospray ionization metal carbonyl mobility 156 23 metal oxides 255 metallocenium 205 methylation 33 mineralization 417 mixed valence 240 molecular architecture molecular design 255 69 187 This page has been reformatted by Knovel to provide easier navigation 429 Index terms Links molecular magnetism 319 molecular oxygen 347 molybdates molybdenum molybdophosphoric acid 55 135 N nanocluster "soluble heterogeneous catalysts" 367 nitronyl nitroxide radical cations 205 nitrosyl derivatives 28 NMR spectra, molybdenum-95 28 nitrogen-14 13 oxygen-17 148 152 154 43 49 164 171 44 phosphorus-31 351 tungsten-183 34 41 vanadium-51 13 354 non-aqueous synthesis O octamolybdate isomers 280 organic pollutants 417 organic-inorganic hybrid materials 269 organoimido derivatives 17 25 organometallic oxides 27 55 oxometal clusters 55 oxonium ion 101 P palladium 97 This page has been reformatted by Knovel to provide easier navigation 430 Index terms paramagnetic NMR pentamolybdate Links 175 28 peroxomolybdates 147 peroxomolybdophosphate 161 peroxoniobates 156 peroxotungstates 151 peroxovanadates 145 photocatalysis 417 photoluminescence 191 Platonic solids 69 polyoxoanions in catalysis 363 polyoxoanion-supported catalysts and catalyst precursors 367 polyoxometalate-polymer hybrids polyoxometalates 55 255 polyoxometallolanthanoates 187 polyoxomolybdate 269 polyoxothiometalates 39 polyoxotungstate 329 polyoxovanadates 255 potential energy surfaces 127 potentiometry 163 protonation 175 89 319 117 Q quinone 347 R rare-earth metal-oxide phosphors 187 redox 347 reductive aggregation 16 This page has been reformatted by Knovel to provide easier navigation 175 205 431 Index terms Links rhenium 55 rhodium 55 ribosome 391 ruthenium 55 247 349 S scanning probe microscopy 329 scanning tunneling microscopy (STM) 329 selenium 89 self-assembled monolayer 329 self-assembly, layer-by-layer 310 small ribosomal subunit (30S) 391 solid state coordination chemistry 269 speciation 169 structural characterization 89 supramolecular chemistry 301 surface reactivity surfactant-encapsulated clusters synthon-based synthesis 305 T tellurium 89 TEM (transmission electron microscopy) 314 terbium 187 thermogravimetry 264 thin films 301 topology 69 toxic metabolites 406 319 417 triangulation numbers 69 tricarbonylmanganese 56 tricarbonylrhenium 56 This page has been reformatted by Knovel to provide easier navigation 432 Index terms TTF (tetrathiafulvalene) tungstates Links 208 242 tungsten 55 V vanadates 12 vanadophosphonates 12 vibrational spectroscopy 101 W water of crystallization 101 Wells-Dawson ion 349 This page has been reformatted by Knovel to provide easier navigation ... Introduction to Polyoxometalate Chemistry: from Topology via Self- Assembly to Applications Synthetic Strategies Rational Approaches to Polyoxometalate Synthesis Functionalization of Polyoxometalates:... Polyoxometalate Chemistry : From Topology via SelfAssembly to Applications M T POPE Department of Chemistry, Georgetown University, Washington DC 20057, USA A MÜLLER Department of Chemistry, University... Photocatalytic Decontamination by Polyoxometalates 417 Index 425 This page has been reformatted by Knovel to provide easier navigation Introduction to Polyoxometalate Chemistry : From