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A Novel Decanuclear Cobalt(II) Cluster

20 Apr 2012

Polynuclear complexes contain several metal atoms or ions in a single coordination species and therefore their electronic structures and magnetic properties can be quite complex. These properties give polynuclear complexes potential for applications in information storage devices and molecular magnets.

Ruren Xu, Jihong Yu and their team at Jilin University, China have reported the synthesis of a novel cobalt(II) polynuclear complex. This new complex is a decanuclear cobalt (II) cluster with bridging Co₃^2-anions and 8-hydroxyquinoline ligands. Interestingly, the ten cobalts are arranged in an adamantane topology which is a chair-like conformation, The adamantane topology of the cobalt culster can be seen clearly in green in the left hand figure. To the researchers’ knowledge, this is the first example of a metallic skeleton with an adamantane topology in a polynuclear complex. It was also found that an antiferromagentic interaction exists within the complex.

This novel complex is unlike any other cobalt polynuclear complex that has been reported before.

To find out more about the fascinating stucture of this decanuclear cobalt (II) cluster, read the full Dalton Transactions article:

A novel decanuclear Co(II) cluster with adamantane-like metallic skeleton supported by 8-hydroxyquinoline and in situ formed CO₃²⁻ anions
Lei Wang, Yi Li, Yu Peng, Zhiqiang Liang, Jihong Yu and Ruren Xu

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Fixing Nitrogen

05 Apr 2012

The well known Haber Bosch process converts nitrogen and hydrogen into ammonia under very harsh reaction conditions. Nitrogen fixation in biology however, takes place at ambient pressure and temperature. A long term goal of researchers has been to achieve nitrogen fixation under ambient conditions.

Whilst molybdenum- and tungsten-dinitrogen complexes containing phosphine ligands are able to reduce nitrogen to ammonia under ambient conditions (in the presence of an acid such as sulfuric acid), these complexes are unable to produce ammonia from molecular dihydrogen.

Yoshiaki Nishibayashi from the University of Tokyo has recently developed a dinitrogen-bridged dimolybdenum complex bearing tridentate PNP pincer ligand which is a diphosphine containing a nitrogen linker. The catalyst is able to produce 23 equivalents of ammonia under atmospheric pressure. A second molybdenum based catalyst, this time bearing ferrocenyl diphosphine ligands is able to produce 226 equivalents of silylamine in the presence of trimethylsilyl chloride and sodium under atmospheric pressure. A future study of the reaction mechanism of these new catalytic systems could provide more insight to guide the design of more effective catalyzed nitrogen fixation in the future.

Nishibayashi has written a comprehensive article that discusses previous work on catalysts for dinitrogen fixation and also reports his recent work on two new nitrogen fixation systems catalyzed by molybdenum-dintrogen complexes. To find out more read the Dalton Transactions Perspective article.

Molybdenum-catalyzed reduction of molecular dinitrogen under mild reaction conditions

Yoshiaki Nishibayashi

Dalton Trans., 2012, Advance Article
DOI: 10.1039/C2DT30105A

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Superior de(hydrogenation)

26 Mar 2012

As the world’s reserves of fossil fuels are fast diminishing, the need for alternative efficient fuels is increasing. Using hydrogen as an energy carrier is attractive for the future since when hydrogen fuel is used in a fuel cell to generate electricity, the only waste product is water. To realise a hydrogen economy, the barriers that need to be overcome are producing hydrogen more efficiently, hydrogen transport and a suitable means of hydrogen storage.

Finding new methods of storing hydrogen is a thriving area of research. The problem we face is that hydrogen storage at ambient pressure and temperature has been a challenge. Xingguo Li and his team are one of the few groups to investigate Mg-Pd films with a transition metal interlayer for hydrogen storage applications. The team have used a technique called magnetron spluttering which is a surface coating technique to produce Mg-Ti-Pd trilayer films.

Most magnesium-based materials for hydrogen storage that have been studied so far have high operating temperatures and so new systems need to be developed that operate at ambient conditions. Xingguo Li and his group have now shown that this is possible by discovering that the trilayer films could be reversibly (de)hydrogenated at ambient temperature – a great improvement on the kinetics of previous magnesium based systems for hydrogen storage.

To learn more about the role that the titanium interlayer plays in the enhancement of Mg-Pd films for hydrogen storage, read the full Dalton Transactions article:

Superior (de)hydrogenation properties of Mg-Ti-Pd trilayer films at room temperature
Gongbiao Xin, Junzhi Yang, Chongyun Wang, Jie Zheng and Xingguo Li
DOI: 10.1039/C2DT30253E

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Cerium cation behaviour could change water splitting studies

13 Mar 2012

Scientists in Germany and Japan have shown that cerium(IV) predominantly forms a dinuclear complex in aqueous solution. Until now, scientists had thought that tetravalent cerium was a monomeric species in aqueous solution. The finding could have important implications for scientists studying water oxidation.

Atsushi Ikeda-Ohno from the Helmholtz-Zentrum Dresden Rossendorf, Dresden, and colleagues used a combination of extended X-ray absorption fine structure and density functional theory calculations to study the cerium(IV) cation. ‘In an aqueous solution, the primary form of metal cations is generally a simple mononuclear hydrate complex or a mononuclear oxo-cation,’ says Ikeda-Ohno, ‘but cerium(IV) forms a unique oxo- or/and hydroxo-bridging dinuclear complex.’

A combined X-ray absorption spectroscopy and density functional calculation study has revealed that a single oxo-bridging dinuclear complex is the dominant form of soluble Ce(IV) species in an aqueous perchloric acid solution.

‘We have always assumed that any reaction between a catalyst and a cerium salt is a one electron transfer reaction,’ says Curtis Berlinguette from the University of Calgary, Canada, who studies the mechanistic behaviour of homogeneous water oxidation catalysts using cerium salts as the terminal oxidant. ‘But if cerium(IV) does exist as a dimer and has an oxo bridge, then it really does question these assumptions and, more importantly, the nature of the oxygen-oxygen bond formation step.’

Berlinguette explains that the current assumption is that you make a catalyst with the metal oxo unit and that reacts with water. But, if the cerium salt that exists in solution contains an oxo, then you could potentially have a combination between the cerium(IV) oxo and the metal oxo, producing oxygen. Therefore, what might appear to be a water oxidation catalyst is in fact just forming dioxygen through reaction with the cerium salt.

‘It would be really interesting if Ikeda-Ohno’s team could extend this study to the acidic conditions and concentrations that are more widely used by the homogeneous catalytic water oxidation community. Then we will have much more insight into what species we are actually studying in solution,’ says Berlinguette.

Ikeda-Ohno says that developing time-resolved systems for X-ray techniques to probe the reactions of the cerium(IV) is the team’s next challenge.

Written by Rachel Cooper

Dinuclear complexes of tetravalent cerium in an aqueous perchloric acid solution
Atsushi Ikeda-Ohno, Satoru Tsushima, Christoph Hennig, Tsuyoshi Yaita and Gert Bernhard
Dalton Trans., 2012, Advance Article
DOI: 10.1039/C2DT12406H

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Keeping it crystalline

08 Mar 2012

When designing new chemical sensors and switches, it is desirable to synthesise materials that are able to retain their structural features even after the uptake of a small molecule. Usually to achieve this, polymeric materials are used with extensive strong bonding that are able to withstand structural changes.

Wojciech Grochala and his team began investigating macrocyclic nickel complexes and discovered a complex that could absorb, then desorb water with retention of its crystallinity. The molecular crystal consists of an almost square planar coordination of nickel(II) supported by a 10 membered, tetradentate sulfur macrocycle. During their investigations, the team discovered that the uptake and release of water vapour was reversible and was accompanied by a change in colour and magnetic susceptibility. The flexible nature of the macrocyclic ligand allows for Ni(12aneS₄)(BF₄)₂ to keep its crystallinity upon water uptake which is rare for molecular crystals and a stark contrast to previously studied coordination polymers.

This exciting finding opens up the possibility of nickel molecular crystals being used as moisture sensors in the future.

To find out more, download the full Dalton Transactions paper:
Chemo-switched chromatic, magnetic and structural changes with retention of molecular crystallinity, Ni(12aneS₄)(BF₄)₂
Andrew J. Churchard, Mariana Derzsi, Zvonko Jagličić, Arndt Remhof and Wojciech Grochala

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Unexpected isomerism

17 Feb 2012

Phenanthroline-based complexes are increasingly finding use in heterogenous catalysis. One class of phenanthroline ligand is neocuproine – a dimethyl substituted derivative which Fabio Ragaini and his team have been interested in to mechanistically study the carbonylation of nitroarenes to carbamates.

When Ragaini et al. started working with the palladium neocuproine complexes, it appeared that minor variations in the synthetic procedure gave products with very different solubility properties, even though the elemental analysis data matched what was expected. In light of this, Ragaini and his team scoured the literature, upon which they discovered inconsistencies regarding the reported solubility of the [Pd(Neoc)X₂] (X = Cl, Br, I) complexes.

Bearing this in mind, Ragaini et al. decided to further investigate the nature of these compounds. They discovered that for each compound in the series, two structural isomers exist: one isomer is neutral and the second is ionic. Formation of the ionic isomer occurs under a much wider range of experimental conditions than the neutral isomer. The ionic isomer must have been synthesised in previous reports even if formation of the neutral one was claimed, say the authors.

It has already been shown that the way palladium–phosphine complexes are synthesised can affect the nature of the final product, in particular its catalytic activity. Ragaini and colleagues’ paper reiterates this for nitrogen-containing ligands and highlights the importance of correctly identifying a product’s structure.

Read the Dalton Transactions article in full to find out more:
Unexpected isomerism in “[Pd(2,9-dimethylphenanthroline)X₂]” (X = Cl, Br, I) complexes: a neutral and an ionic form exist
Martino Rimoldi, Fabio Ragaini, Emma Gallo, Francesco Ferretti, Piero Macchi and Nicola Casati

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Silver Complexes Kill Cancer Cells

08 Feb 2012

Cisplatin is a well known chemotherapy drug used to treat a range of cancers. While the drug can be an effective treatment there are notable unwanted side-effects, which can include nausea, vomiting, kidney damage and loss of hearing. This new research from Leeds University by Charlotte Willans et al. details the activity of a range of silver complexes containing N-heterocyclic carbene (NHC) ligands which show comparable and even enhanced cytotoxicity compared to cisplatin. As the compounds don’t contain platinum they are likely to be less toxic and therefore exhibit fewer and less severe side-effects.

The team synthesised a series of monodentate, bidentate and macrocyclic cationic silver bis(NHC) complexes and tested their activity with cell lines of breast and colon cancer (MCF7 and DLD1 lines respectively). They found that the bidentate complexes showed enhanced cytotoxicity over the monodentate and macrocyclic ligands, which were similar to cisplatin. As yet the exact mechanisms of action are still unclear but are likely linked to the stabilities of the complexes.

For more information about this exciting research you can download the article which is free to access for 4 weeks. You can also keep up to date with all the latest news in inorganic chemistry by following us on twitter or signing up to the Dalton Transactions e-alert service.

Enhanced cytotoxicity of silver complexes bearing bidentate N-heterocyclic carbene ligands
Charlotte E. Willans, Diana C F Monteiro, Roger M Phillips, Benjamin D Crossley and Jake Fielden
Dalton Trans., 2012, Accepted Manuscript
DOI: 10.1039/C2DT12399A

Also of interest from the collection ‘Highlights in Chemistry’

Therapeutic applications of gold complexes: lipophilic gold(III) cations and gold(I) complexes for anti-cancer treatment
Chi-Ming Che and Raymond Wai-Yin Sun
Chem. Commun., 2011, 47, 9554-9560
DOI: 10.1039/C1CC10860C, Highlight

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Dalton Transactions Blog

Archive for the ‘News’ Category

A Novel Decanuclear Cobalt(II) Cluster

Fixing Nitrogen

Top ten most accessed articles in February

Superior de(hydrogenation)

Cerium cation behaviour could change water splitting studies

Keeping it crystalline

Top ten most accessed articles in January

Unexpected isomerism

Silver Complexes Kill Cancer Cells

Top ten most accessed articles in December

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