Leah Morris, Web Writer – Page 2 – Dalton Transactions Blog

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Photochemical carbon dioxide reduction

29 Jun 2012

Photochemical reduction of greenhouse gas, carbon dioxide into higher energy content fuels is attractive because it utilises a renewable energy source – the sun. Most catalysts that are already used for this process (TiO₂and metallic clusters based on Cu, Pt and Rh) need ultraviolet light for excitation and have a low conversion efficiency, prohibiting wide scale industrial application.

There is need for a photocatalyst that is efficient, low cost and can be excited by visible light.

Zhi-Gang Zou and his team at Nanjing University have synthesised an air stable copper (I) bipyridine complex which binds to TiO₂. The Cu(I)complex/TiO₂ hybrid system when irradiated with visible light can reduce CO₂to CH₄ with high efficiency and selectivity.

This is an exciting development — no other products were formed during photoreduction of carbon dioxide and copper is an inexpensive and abundant metal. The possiblilty for using copper complexes in carbon dioxide reduction catalysis has now been opened up for further work…

To find out more (including how Zou and team also used the complex in a dye-sensitised solar cell), read the full Dalton Transactions article:

A Copper(I) Dye-Sensitized TiO₂-Based System for Efficient Light Harvesting and Photoconversion of CO₂ into Hydrocarbon Fuel
Yong-Jun Yuan, Z.T. Yu, Jiyuan Zhang and Zhigang Zou

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Fast Synthesis of C-dots

18 Jun 2012

Quantum dots are nanoparticles of semiconductor material which, because of their very small size, display different optical and electrical properties to that of the corresponding material in the bulk phase. Traditional semiconductor quantum dots are used in optical applications such as cell imaging, LEDs and photodetectors due to their high extinction coefficient.

Due to their cheaper cost and intrinsic low toxicity, carbon nanodots (C-dots) have the potential to replace traditional semiconductor quantum dots. To overcome some of the drawbacks with previous methods of fabricating C-dots, Zhenui Kang and his team at Soochow University, China have developed a facile one step electrochemical synthesis. This exciting new method produces c-dots of high purity and uses only pure water as an electrolyte, which is attractive because it is low cost and more environmentally friendly .

The team also synthesized nanohybrid TiO₂/C-dots which possess good photocatalytic activity.

To find out more about the photoluminescence and photocatalytic properties of C-dots, read the full Dalton Transactions article…

Large Scale Electrochemical Synthesis of High Quality Carbon Nanodots and Their Photocatalytic Property
Zhenhui Kang, Hai Ming, Zheng Ma, Yang Liu, Keming Pan, Hang Yu and Fang Wang

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Hydrogenase Hydrogel

24 May 2012

The ability of hydrogenase enzymes to reversibly catalyse the reduction of protons to form molecular hydrogen (H₂) has attracted a great deal of research interest. Synthetic mimics of the hydrogenase active site could potentially replace expensive platinum catalysts in hydrogen fuel cells. Currently these mimics are significantly less efficient than the natural enzyme and they are oxygen sensitive. It is thought that by creating a stable peptide based enviroment around the mimic, the stability and efficiency could be improved.

Encapsulating a hydrogenase mimic into a hydrogel causes a restriction in isomerisation after photolysis

Researchers from the Hunt and Ulijn groups at the University of Strathclyde and the Pickett group from the University of East Anglia have successfully encapsulated a [FeFe]-hydrogenase active site mimic into a dipeptide based hydrogelator. Their research has shown that there is a stark difference in the behaviour of the active site mimic in the gel phase compared to the solution phase. Experiments show that the mimic is significantly more stable in the gel phase and is less senstive to water and UV light which could potentially help to improve catalytic activity.

To find out more, read the full Daltons Transactions article…

Encapsulating [FeFe]-hydrogenase model compounds in peptide hydrogels dramatically modifies stability and photochemistry
Pim Wilhelmus, Johannes Maria Frederix, Rafal Kania, Joseph A Wright , Dimitrios A Lamprou, Rein Ulijn, C J Pickett and Neil T Hunt.

This article is part of the upcoming Dalton Discussion themed issue on Inorganic Photophysics and Photochemistry – Fundamentals and Applications

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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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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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Organoimido derivatives of POMs

27 Feb 2012

Polyoxometalates (POMs) are interesting inorganic compounds that contain transition metal ions linked together by bridging oxygen atoms to form large three dimensional frameworks. Even though POMs have been studied for a long time (the first polyoxometalate was reported nearly 200 years ago by the Swedish chemist, Jons Jacob Berzelius), there has been limited success in producing practical and functional materials.

By replacing the oxo bridging groups with organic ligands, researchers can develop new strategies for synthesising novel POM-based organic-inorganic hybrid materials through linking POMs and organic compounds together by covalent bonds. Of particular interest are the organoimido POM derivatives.

In their latest HOT Perspective article, a team of researchers from Tsinghua University, China, explore the synthetic chemistry of organoimido derivatives of POMs and the reactive chemistry for the construction of POM-based hybrid materials. Wei et al. highlight that both the inorganic cluster skeleton and the organic ligand in organoimido-based POMs can act as reactive sites which could lead to an exciting future for the chemistry of organoimido based POMs.

To find out more, download the full article which is free to access until 26^th March…
The chemistry of organoimido derivatives of polyoxometalates
Jin Zhang, Fengping Xiao, Jian Hao and Yongge Wei

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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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Using the ‘multicomponent’ strategy to improve hydrogen storage materials

07 Feb 2012

The need for a hydrogen storage material that can store hydrogen reversibly, with little or no kinetic barrier, and at ambient conditions remains a great challenge for researchers in this field. In order to progress towards a future hydrogen economy, hydrogen storage materials must also be practical for mobile applications and of course be economically viable.

Many different materials have been proposed for hydrogen storage. These range from physisorption materials such as activated carbons, zeolites and Metal Organic Frameworks (MOFs) to materials based on chemisorption such as metal hydrides, ammonia boranes and alanates. The hydrogen binding mechanism of chemisorption materials is through the formation of strong covalent bonds with hydrogen and so even though they have high hydrogen storage capacities, the drawback is that due to their high hydrogen binding enthalpies, the materials must be heated to remove H₂.

To improve the unfavorable thermodynamics and poor kinetics of complex hydrides, researchers have successfully applied a ‘multicomponent’ strategy whereby two compounds are mixed together to form a multinary phase. The mixed LiNH₂–MgH₂ system is a successful example of the employment of the ‘multicomponent’ strategy to improve the characteristics of complex hydrides for hydrogen storage. Applying this method to metal amidoborane systems is an exciting prospect.

With this in mind, Chen et al. synthesized a Li–Na mixed amidoborane, Na[Li(NH₂BH₃)₂] using a wet-chemical method. Using first-principles techniques, the team were able to explore the likelihood of the existence of multicomponent Li–Na amidoboranes with varying Li/Na ratios. They discovered that the dehydrogenation temperature of Na[Li(NH₂BH₃)₂] is lower than that of lithium or sodium amidoboranes and determined that this could be due to a stronger dihydrogen bond interaction and a moderate hydrogen atom removal energy. They also proposed the mechanism for the first-step dehydrogenation.

To find out more, read the Dalton Transactions full paper…

Li–Na ternary amidoborane for hydrogen storage: experimental and first-principles study

Wen Li, Ling Miao, Ralph H. Scheicher, Zhitao Xiong, Guotao Wu, C. Moysés Araújo, Andreas Blomqvist, Rajeev Ahuja, Yuanping Feng and Ping Chen

DOI: 10.1039/C2DT11819J

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