In chemistry, a polyoxometalate (abbreviated POM) is a polyatomic ion, usually an anion, that consists of three or more transition metal oxyanions linked together by shared oxygen atoms to form closed 3-dimensional frameworks. The metal atoms are usually group 6 (Mo, W) or less commonly group 5 (V, Nb, Ta) transition metals and Tc in their high oxidation states. Polyoxometalates are often colorless, orange or red diamagnetic anions. Two broad families are recognized, isopolymetalates, composed of only one kind of metal and oxide, and heteropolymetalates, composed of one metal, oxide, and a main group oxyanion (phosphate, silicate, etc.). Many exceptions to these general statements exist. The oxides of d0 metals such as , , dissolve at high pH to give orthometalates, , , . For and , the nature of the dissolved species at high pH is less clear, but these oxides also form polyoxometalates. As the pH is lowered, orthometalates protonate to give oxide–hydroxide compounds such as and . These species condense via the process called olation. The replacement of terminal M=O bonds, which in fact have triple bond character, is compensated by the increase in coordination number. The nonobservation of polyoxochromate cages is rationalized by the small radius of Cr(VI), which may not accommodate octahedral coordination geometry. Condensation of the species entails loss of water and the formation of linkages. The stoichiometry for hexamolybdate is shown: 6 MoO4^2- + 10 HCl -> [Mo6O19]^2- + 10 Cl- + 5 H2O An abbreviated condensation sequence illustrated with vanadates is: 4 VO4^3- + 8 H+ -> V4O12^4- + 4 H2O 5 V4O12^4- + 12 H+ -> 2 V10O26(OH)2^4- + 4 H2O When such acidifications are conducted in the presence of phosphate or silicate, heteropolymetalate result. For example, the phosphotungstate anion consists of a framework of twelve octahedral tungsten oxyanions surrounding a central phosphate group. Ammonium phosphomolybdate, anion, was reported in 1826. The isostructural phosphotungstate anion was characterized by X-ray crystallography 1934.

About this result
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
Related lectures (2)
Forced Oscillations in 1D: General Regime
Explores the general forced regime in 1D oscillators and methods for solving equations.
Show more
Related publications (26)

Orientational Self-Sorting in Octahedral Palladium Cages: Scope and Limitations of the “cis Rule”

Kay Severin, Farzaneh Fadaei Tirani, Damien Wen Chen, Jean Charles Edouard de Montmollin, Atena-Bianca Solea

Octahedral coordination cages of the general formula Pd6L1212 were obtained by combining Pd(CH3CN)42 with heteroditopic N-donor ligands. Four different ligands were employed. These ligands have 3-pyridyl donor groups at one end and 4-pyridyl, ...
2024

Hybrid organic/metal-oxide shells on semiconductor nanocrystals via colloidal atomic layer deposition

Ona Segura Lecina

The escalating energy demand and the imperative necessity to reduce the carbon footprint require transformative approaches to energy conversion. Materials chemistry plays a pivotal role in addressing these global challenges by developing novel materials fo ...
EPFL2024

Synthetic Receptors with Micromolar Affinity for Chloride in Water

Kay Severin, Farzaneh Fadaei Tirani, Damien Wen Chen, Cesare Berton, Sylvain Alexandre Marie Sudan

A water-soluble coordination cage was obtained by reaction of Pd(NO3)2 with a 1,3-di(pyridin-3-yl)benzene ligand featuring a short PEG chain. The cavity of the metal-organic cage contains one nitrate anion, which is readily replaced by chloride. The appare ...
Wiley2023
Show more
Related concepts (6)
Bridging ligand
In coordination chemistry, a bridging ligand is a ligand that connects two or more atoms, usually metal ions. The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually restricted to small ligands such as pseudohalides or to ligands that are specifically designed to link two metals. In naming a complex wherein a single atom bridges two metals, the bridging ligand is preceded by the Greek letter mu, μ, with a subscript number denoting the number of metals bound to the bridging ligand.
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical.
Technetium
Technetium is a chemical element with the symbol Tc and atomic number 43. It is the lightest element whose isotopes are all radioactive. All available technetium is produced as a synthetic element. Naturally occurring technetium is a spontaneous fission product in uranium ore and thorium ore, the most common source, or the product of neutron capture in molybdenum ores. This silvery gray, crystalline transition metal lies between manganese and rhenium in group 7 of the periodic table, and its chemical properties are intermediate between those of both adjacent elements.
Show more

Graph Chatbot

Chat with Graph Search

Ask any question about EPFL courses, lectures, exercises, research, news, etc. or try the example questions below.

DISCLAIMER: The Graph Chatbot is not programmed to provide explicit or categorical answers to your questions. Rather, it transforms your questions into API requests that are distributed across the various IT services officially administered by EPFL. Its purpose is solely to collect and recommend relevant references to content that you can explore to help you answer your questions.