Clusters Of Early Transition Metals Research Articles

Luminescent and self-healing hybrid ionotropic hydrogel beads of ammonium metavanadate and chitosan: promising biomaterial as an antimicrobial agent, efficient dye adsorbent and ascorbic acid sensor.

Biopolymers have received widespread attention due to their beneficial characteristics, such as like easy processing, biodegradability and biocompatibility. Concurrently, inorganic polyoxometalates (POMs), a class of metal-oxygen anionic and nanosized clusters of early transition metals, have a wide range of attractive functions and are used in biomedical and industrial fields. In this communication, we report a simple approach to create ammonium metavanadate (AMV)-biopolymer composite hydrogel beads that combine the advantages of biopolymers and POM clusters. Crosslinking was achieved through electrostatic interactions between cationic chitosan, chitosan/gelatin, chitosan/methylcellulose and AMV (NH4VO3). The as-prepared hydrogel beads were yellow in colour and exhibited a high mechanical strength. They were characterized using FT-IR spectroscopy and SEM, to confirm hydrogel formation and evaluate their surface morphology. It was demonstrated that the fabricated hydrogel blend possessed tuneable physicochemical properties, good swelling behaviour (with a maximum swelling of 432%), excellent luminescence and adsorption, and remarkable biomedical properties. Batch adsorption experiments demonstrated that the beads had an equilibrium adsorption capacity of 539 mg g-1 for the removal of Congo red dye from aqueous solutions, which was more efficient than the most reported natural biosorbents. Due to their luminescence properties these hydrogel beads showed excellent selective sensing behaviour toward ascorbic acid with a LOD of 1.06 μM. The hydrogels were also assessed for their antibacterial activity, and were tested against Staphylococcus aureus, Escherichia coli, Streptococcus anginosus, and Klebsiella pneumoniae. The cytotoxicity results showed that the embedded POMs exhibited dose-dependent cytotoxicity against the embryonic kidney cell line (HEK).

Aqueous biphasic system in differential extraction of arseno and phospho molybdenum blue: Consequent sensing of glutathione in acid-free medium

Polyoxometalates (POMs) are the oxyanion clusters of early transition metals (mostly molybdenum (VI), tungsten (VI) and vanadium (V)) and they show interesting properties particularly in the field of catalysis and sensing chemistry. In this work molybdenum blue (MB), phosphomolybdenum blue (PMB) and arsenomolybdenum blue (AsMB) are prepared using glutathione (GSH) as reducing agent in acid–free condition. The MB species are further characterised by UV–vis spectroscopy, Raman spectroscopy, XPS, powder XRD and FTIR spectroscopy. The prepared MB solutions showed an exciting behaviour in Aqueous Biphasic Systems (ABS) using PEG#4000 and Na2SO4 as phase forming components. MB and PMB partition to the micellar medium of PEG upto 44 % and 66 % respectively but AsMB is not at all partitioned. Therefore the method is useful for differentiating PMB and AsMB. PEG has been recovered using ultra-filtration technique after the ABS. The experiment also reveals that GSH, a biomolecule with high physiological impact, can be detected at trace concentrations by PMB formation method both in water and blood serum media.

Symmetric Redox Flow Batteries with Bifunctional Molecules

The continued integration of renewable energy sources into the power grid, as well as the development of decentralised energy systems, requires energy storage in order to capture and store the energy produced intermittently from renewable sources. One energy storage option is the Redox Flow Battery (RFB) which has several advantages over other secondary batteries. As the active species of an RFB remain in solution during charge and discharge, degradation of the electrodes is minimised. Further, due to external storage of the electrolytes, the energy and power of an RFB can be adjusted independently by varying the volume of stored electrolyte or size of the cell stack. The most mature RFB is the all-vanadium RFB but this also has drawbacks, such as slow electron transfer kinetics of the vanadium ions1 and a requirement for the use of acidic electrolytes. Polyoxometalates (POMs) are anionic metal-oxygen clusters of early transition metals, commonly vanadium, molybdenum and tungsten, which can undergo redox reactions in which multiple electrons are transferred. The electrochemical properties of POMs prompted their investigation by our group and the development of a POM RFB which was based on the reactions of [PV14O42]9- at the cathode and [SiW12O40]4- at the anode.2 This work demonstrated that an RFB cell with multi-electron redox reactions occurring in each half-cell could be created by using POMs and that the charge transfer reactions of POMs are relatively fast.2 The [PV14O42]9-/[SiW12O40]4- RFB was classified as an asymmetric RFB due to the use of different POM active species in each half-cell. Alternatively, symmetric RFBs can be designed which utilise the same active material in both half-cells. Our group has also investigated the approach of using bifunctional molecules, which can undergo redox reactions at positive and negative potentials, as the active species in symmetric RFBs. This includes the use of fullerene species functionalised with ferrocene units.3 POMs can also be bifunctional species when composed of two different redox-active metals. In this poster, we outline the results of work in our group on the use of bifunctional species in symmetric RFBs, including the study of a POM for a symmetric RFB which has shown good stability in charge-discharge testing so far in conditions that are only mildly acidic. References J. Friedl and U. Stimming, Electrochimica Acta, 2017, 227, 235–245.J. Friedl, M. V. Holland-Cunz, F. Cording, F. L. Pfanschilling, C. Wills, W. McFarlane, B. Schricker, R. Fleck, H. Wolfschmidt and U. Stimming, Energy Environ. Sci., 2018, 11, 3010–3018.J. Friedl, M. A. Lebedeva, K. Porfyrakis, U. Stimming and T. W. Chamberlain, J. Am. Chem. Soc., 2018, 140, 401–405.

Incorporation of Polyoxometalates into Polymers to Create Linear Poly(polyoxometalate)s with Catalytic Function.

Organic polymers have been found widespread commercial applications due to their easy processing and attractive mechanical properties. Concurrently, inorganic polyoxometalates (POMs), a class of metal-oxygen anionic and nanosized clusters of early transition metals, have a wide range of attractive functions and are used in industrial catalysis. In this communication, we report a new approach to creating the first linear poly(polyoxometalate)s that combine the advantages of polymers and POM clusters. In the experiment, a POM-containing norbornene monomer was first synthesized by linking a Wells-Dawson-type POM with a norbornene derivative. The monomer was polymerized in the presence of a Grubbs catalyst under mild conditions with yields nearly 100% in a living and controllable manner. The resulting poly(polyoxometalate)s have controllable molecular weights and a well-defined hybrid structure of an organic polynorbornene backbone with large pendant groups of the nanosized POM clusters. Thus, they form good films and have a good catalytic performance. Our findings not only pave the way for incorporating the POM clusters into polymers with well-defined structures and high molecular weights, but also offer a competitive strategy for developing more novel catalytic systems by introducing the poly(polyoxometalate)s.

Polyoxometalates: formation, structures, principal properties, main deposition methods and application in sensing

Today, sensing represents one of the key topics in current science and technology. Polyoxometalates (POMs), which are defined as early transition metal clusters, are considered as one of the most growing fields of research and development in sensing. This paper discusses the promising prospects of POMs in sensing. The paper starts with brief definitions about the formation of POMs. The two basic structures of POMs, Keggin and Dawson, as well as some combined structures are discussed. The interesting properties of POMs particularly as acid catalysts, in medicine, in redox chemistry and in magnetism are briefly mentioned. The main methods used for the deposition of POMs on solid supports (substrates) including chemisorption, electrodeposition, encapsulation in polymers and sol–gels, immobilization using the Langmuir–Blodgett process, layer by layer assemblies as well as deposition via formation of hybrid POM–organic moieties are discussed with their advantages and disadvantages. Finally, the potential applications of immobilized POMs on solid substrates as sensors for the detection and determination of analytes both in liquid and in the gas phase are addressed and compared.

Surface-Mediated Synthesis and Spectroscopic Characterization of Tantalum Clusters on Silica

Tantalum clusters were synthesized on the surface of porous silica by treatment of adsorbed Ta(CH(2)Ph)(5) in H(2) at temperatures in the range of 523-723 K. The surface species were characterized by UV-vis, far-infrared, and extended X-ray absorption fine-structure (EXAFS) spectroscopies, each of which provided evidence of Ta-Ta bonds similar to those in well-characterized molecular tantalum clusters. The Ta-Ta distance determined by EXAFS spectroscopy was 2.93 A. The chemistry of the cluster synthesis is similar to that of syntheses of similar tantalum clusters in solution. The supported clusters formed at 523 K are characterized by an EXAFS first-shell Ta-Ta coordination number of nearly 2, indicative of tri-tantalum clusters, although it is expected that a mixture of clusters was present, and reduction in H(2) at higher temperatures led to larger tantalum clusters. This is the first example of the surface-mediated synthesis of an early transition metal cluster, and the supported clusters reported here are the first to have been characterized by all three of the spectroscopic methods mentioned above. The similarity of the surface synthesis to that in solution points to opportunities to extend this new class of material to other early transition metal clusters on various supports.

High Hydride Count Rhodium Octahedra, [Rh6(PR3)6H12][BArF4]2: Synthesis, Structures, and Reversible Hydrogen Uptake under Mild Conditions

A new class of transition metal cluster is described, [Rh(6)(PR(3))(6)H(12)][BAr(F)(4)](2) (R = (i)Pr (1a), Cy (2a); BAr(F)(4) = [B{C(6)H(3)(CF(3))(2)}(4)](-)). These clusters are unique in that they have structures exactly like those of early transition metal clusters with edge-bridging pi-donor ligands rather than the structures expected for late transition metal clusters with pi-acceptor ligands. The solid-state structures of 1a and 2a have been determined, and the 12 hydride ligands bridge each Rh-Rh edge of a regular octahedron. Pulsed gradient spin-echo NMR experiments show that the clusters remain intact in solution, having calculated hydrodynamic radii of 9.5(3) A for 1a and 10.7(2) A for 2a, and the formulation of 1a and 2a was unambiguously confirmed by ESI mass spectrometry. Both 1a and 2a take up two molecules of H(2) to afford the cluster species [Rh(6)(P(i)Pr(3))(6)H(16)][BAr(F)(4)](2) (1b) and [Rh(6)(PCy(3))(6)H(16)][BAr(F)(4)](2) (2b), respectively, as characterized by NMR spectroscopy, ESI-MS, and, for 2b, X-ray crystallography using the [1-H-CB(11)Me(11)](-) salt. The hydride ligands were not located by X-ray crystallography, but (1)H NMR spectroscopy showed a 15:1 ratio of hydride ligands, suggesting an interstitial hydride ligand. Addition of H(2) is reversible: placing 1b and 2b under vacuum regenerates 1a and 2a. DFT calculations on [Rh(6)(PH(3))(6)H(x)()](2+) (x = 12, 16) support the structural assignments and also show a molecular orbital structure that has 20 orbitals involved with cluster bonding. Cluster formation has been monitored by (31)P{(1)H} and (1)H NMR spectroscopy, and mechanisms involving heterolytic H(2) cleavage and elimination of [HP(i)Pr(3)](+) or the formation of trimetallic intermediates are discussed.

Early transition metal clusters with π-donor ligands edited by M. H. Chisholm

<i>Early transition metal clusters with π-donor ligands</i> edited by M. H. Chisholm

A statistical analysis of magic numbers of valence electrons in small clusters of transition metals using the Cambridge Crystal Structure Database

Distribution of small clusters of transition metals M n with n = 3 to 6 metal atoms over the number of valence electrons in metallopolyhedra, N val, has been analysed using the Cambridge Crystal Structure Database (10 sets, total 923 crystal structures). The occurrence of peaks related to magic numbers N val has been found for trinuclear (48e), tetranuclear (60e) and hexanuclear (86e) carbonyl clusters of metals of the Fe and Co subgroups. However, similar distributions for pentanuclear carbonyl clusters of the same metals, for tri- and tetranuclear carbonyl-phosphine derivatives of metals of the Ni subgroup, and also for the M 4(μ 3-X) 4 type clusters with mixed cubane-like frameworks (where X is a halogen or chalcogen) are more uniform and exhibit no predominance of specific “magic” numbers. Among tri- and tetranuclear metal complexes of the Cu subgroup, the more common and typical are those with no metal-metal bonds, in which every metal atom has a 17-, 18-, or 19-electron valence shell. On going from metals of the Fe and Co subgroups to post-transition elements, the strength of metal-metal bonds and the descriptive ability of magic numbers decline. The following magic numbers were found for octahedral “inorganic” clusters of early transition metals: N val = 74 for clusters of the M 6(μ 3-X) 12 type (where X is a halogen) and a more strictly obeyed number N val=84 valid for more rigid frameworks M 6(μ 3-X) 8, (X is halogen or chalcogen).

Theoretical evidence for a paramagnetic ground state of the cluster ion [(η5-C5Me5)3Re3(µ2-O)6]2+

The electronic structure of uncapped trinuclear clusters of early transition metals with six µ2 bridging and three terminal arene ligands (η5, η6) has been analysed, a triplet ground state being predicted for the recently synthesized cluster ion [(η5-C5Me5)3Re3(µ2-O)6]2+, at variance with the reported interpretation of n.m.r. data, which indicates diamagnetism.

Trinuclear clusters of early transition metals: Jahn-Teller distortions and electronic structure

Calculs de la structure electronique de Mo 3 S 2 Cl 9 3− par la methode de Huckel generalisee. Conclusions generales sur l'effet des coordinats terminaux, portants ou chapeautants sur les structures electroniques et geometriques

Reactions of the early transition metal clusters with aliphatic alcohols. Part I. Preparation, properties, and structural classification of [M6Cl12](OH)2 · 6 H2O · 2 CH3OH (M  Nb, Ta)

AbstractThe conditions of preparation of the crystalline compounds of the type [M6Cl12] (OH)2 · 6 H2O · 2 CH3OH, M  Nb, Ta, have been described. According to the X‐ray diffraction patterns, it is not possible to classify these isomorphous substances, in the five already known structural groups of [M6X12]2+ clusters of niobium and tantalum. Physical and spectral properties of these compounds are compared with the corresponding octahydrates [M6X12](OH)2 · 8 H2O and other clusters of niobium and tantalum.