Stabilization of High-Valence Ruthenium with Silicotungstate Ligands: Preparation, Structural Characterization, and Redox Studies of Ruthenium(III)-Substituted α-Keggin-Type Silicotungstates with Pyridine Ligands, [SiW11O39RuIII(Py)]5−

Keggin type phosphotungstic acid intercalated copper-chromium-layered double hydroxide reinforced porous hollow fiber as a sorbent for hollow fiber solid phase microextraction of selected chlorophenols besides their quantification via high performance liquid chromatography

Herein, a copper-chromium-layered double hydroxide (Cu/Cr-LDH) was synthesized by the co-precipitation method. The Cu/Cr-LDH was intercalated to the Keggin-type polyoxometalate (H₃PW₁₂O₄₀). The modified LDH accommodated in the pores of hollow fiber (HF), to prepare the extracting device for the HF-solid phase microextraction method (HF-SPME). The method was used for the extraction of 4-chlorophenol, 2,4-dichlorophenol, and 2,4,6- trichlorophenol from tap water, river water, and tea sample. The extracted target analytes were quantified via high-performance liquid chromatography-UV detection. The figures of merit of the method such as, linear dynamic ranges (LDRs), limit of detections (LODs) and, limit of quantifications (LOQs), were determined based on the obtained optimum condition. Based on the results, the LDR was between 1 and 500 μg L ^- 1 and r² higher than 0.9960. The LODs and LOQs were obtained in the ranges of 0.28-0.36 µg L ^- 1 and 0.92-1.1 µg L ^- 1, respectively. The relative standard deviations ((RSDs% for inter-and intra-day) of the method for the extraction of target analytes were calculated in two different concentrations of (2 and 10 μg L ^- 1) and (5 and 10 μg L ^- 1) between 3.70% - 5.30% and 3.50% - 5.70%-respectively. The enrichment factors were obtained between 57 and 61. In order to investigate the accuracy of the method, also the relative recovery was obtained, between 93 and 105%. Finally, the proposed method was used for the extraction of the selected analytes in different water and tea samples.

Easy Ligand Activation in the Coordination Sphere of Ru inside the [PW11O39]7- Backbone

Irradiation of the Keggin-type [PW₁₁O₃₉{Ru(NO)}]⁴⁻ (Ru-NO) polyoxometalate in CH₃CN results in rapid NO ligand elimination with the formation of [PW₁₁O₃₉{Ru^III(CH₃CN)}]⁴⁻ (Ru-CH₃CN). This complex offers an easy entry into the Ru-based chemistry of the {PW₁₁Ru} complex. Attempts to substitute N₃⁻ for CH₃CN in the presence of an NaN₃ excess lead a variety of products: (i) [PW₁₁O₃₉{Ru^III(N₃)}]⁴⁻ (Ru-N₃); (ii) [PW₁₁O₃₉{Ru^III(N₄HC-CH₃)}]⁴⁻ (Ru-Tz) as a click-reaction product; and (iii) [PW₁₁O₃₉{Ru^II(N₂)}]⁵⁻ (Ru-N₂). UV-VIS, CV, and HR-ESI-MS techniques were used for the reaction monitoring and characterization of the products.

Hybrid polyoxometalates as post-functionalization platforms: from fundamentals to emerging applications

Polyoxometalates (POMs) represent an important group of metal-oxo nanoclusters, typically comprised of early transition metals in high oxidation states (mainly V, Mo and W). Many plenary POMs exhibit good pH, solvent, thermal and redox stability, which makes them attractive components for the design of covalently integrated hybrid organic-inorganic molecules, herein referred to as hybrid-POMs. Until now, thousands of organic hybrid-POMs have been reported; however, only a small fraction can be further functionalized using other organic molecules or metal cations. This emerging class of 'post-functionalizable' hybrid-POMs constitute a valuable modular platform that permits coupling of POM properties with different organic and metal cation functionalities, thereby expanding the key physicochemical properties that are relevant for application in (photo)catalysis, bioinorganic chemistry and materials science. The post-functionalizable hybrid-POM platforms offer an opportunity to covalently link multi-electron redox responsive POM cores with virtually any (bio)organic molecule or metal cation, generating a wide range of materials with tailored properties. Over the past few years, these materials have been showcased in the preparation of framework materials, functional surfaces, surfactants, homogeneous and heterogeneous catalysts and light harvesting materials, among others. This review article provides an overview on the state of the art in POM post-functionalization and highlights the key design and structural features that permit the discovery of new hybrid-POM platforms. In doing so, we aim to make the subject more comprehensible, both for chemists and for scientists with different materials science backgrounds interested in the applications of hybrid (POM) materials. The review article goes beyond the realms of polyoxometalate chemistry and encompasses emerging research domains such as reticular materials, surfactants, surface functionalization, light harvesting materials, non-linear optics, charge storing materials, and homogeneous acid-base catalysis among others.

Reactions of [Ru(NO)Cl5]2- with pseudotrilacunary {XW9O33}9- (X = AsIII, SbIII) anions

Reactions of [Ru(NO)Cl₅]^2- with pseudotrivacant B-α-[XW₉O₃₃]^9- (X = As^III, Sb^III) at 160 °C result in the rearrangement of polyoxometalate backbones into {XM₁₈} structures. In the case of arsenic, oxidation of As^III to As^V takes place with the formation of a mixture of plenary and monosubstituted Dawson [As₂W₁₈O₆₂]^6- and [As₂W₁₇Ru(NO)O₆₁]^7- anions, of which the latter was isolated as Me₂NH₂⁺ (DMA-1a and DMA-1b) and Bu₄N⁺ (Bu₄N-1) salts and fully characterized. Both α₁ and α₂ isomers of [As₂W₁₇Ru(NO)O₆₁]^7- were present in the reaction mixture; pure [α₂-As₂W₁₇Ru(NO)O₆₁]^7- was isolated as the Bu₄N⁺ salt. In the case of antimony, [SbW₉O₃₃]^9- is converted into a mixture of [SbW₁₈O₆₀]^9- and [SbW₁₇{Ru(NO)}O₅₉]^10-. The formation of trisubstituted [SbW₁₅{Ru(NO)}₃O₅₇]^12- as a minor byproduct was detected by HPLC-ICP-AES. The monosubstituted [SbW₁₇{Ru(NO)}O₅₉]^10- anion was isolated as DMAH⁺ (DMA-2) and mixed inorganic cation (CsKNa-2) salts and characterized by XRD, HPLC-ICP-AES, EA and TGA techniques. X-ray analysis shows the presence of the {Ru(NO)}-group in the 6-membered ("equatorial") belt of the Sb-free hemisphere. The experimental findings were confirmed and interpreted by means of quantum chemical calculations.

Preparation of α1- and α2-isomers of mono-Ru-substituted Dawson-type phosphotungstates with an aqua ligand and comparison of their redox potentials, catalytic activities, and thermal stabilities with Keggin-type derivatives

Both the α1- and the α2-isomers of mono-ruthenium (Ru)-substituted Dawson-type phosphotungstates with terminal aqua ligands, [α1-P2W17O61Ru(III)(H2O)](7-) (α1-RuH2O) and [α2-P2W17O61Ru(III)(H2O)](7-) (α2-RuH2O), were prepared in pure form by cleavage of the Ru-S bond of the corresponding DMSO derivatives, [α1-P2W17O61Ru(DMSO)](8-) (α1-RuDMSO) and [α2-P2W17O61Ru(DMSO)](8-) (α2-RuDMSO), respectively. Redox studies indicated that α1-RuH2O and α2-RuH2O show proton-coupled electron transfer (PCET), and the Ru(III)(H2O) species was reversibly reduced to Ru(II)(H2O) species and oxidized to Ru(IV)([double bond, length as m-dash]O) species and further to Ru(V)([double bond, length as m-dash]O) species in aqueous solution depending on the pH. Their redox potentials and thermal stabilities were compared with those of the corresponding α-Keggin-type derivatives ([α-XW11O39Ru(H2O)](n-); X = Si(4+) (n = 5), Ge(4+) (n = 5), or P(5+) (n = 4)). The basic electronic and redox features of Ru(L)-substituted Keggin- and Dawson-type heteropolytungstates (with L = H2O or O(2-)) were analyzed by means of density functional calculations. Similar to the corresponding α-Keggin-type derivatives, both α1-RuH2O and α2-RuH2O show catalytic activity for water oxidation.

Redox chemistry of ruthenium ions in mono-substituted Keggin tungstophosphate: a new synthetic extension for ruthenium derivatives based on [PW11O39RuVIN]4−

A facile approach to ruthenium-substituted Keggin-type heteropolyoxotungstates with high yield by easily controllable redox reaction is described.