Archive for the ‘Hot Articles’ Category

Using the ‘multicomponent’ strategy to improve hydrogen storage materials

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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Hot Article: The difference a solvent makes

Zinc alkyl complexes have an interesting role in a wide variety of stoichiometric and catalytic transformations and understanding how the ligands affect reactivity is important in understanding these structures and their reactivity. This Hot Article from Andrew Wheatley and Janusz Lewinski et al. details experiments involving the reactions of Et2Zn with a bicyclic guanidine.

 

Exposure of the produced complex (EtZn(hpp)) to undried air alters the composition depending on whether THF or CH2Cl2 is used as the solvent (displayed above). You can read the full details of the teams investigation by downloading their article below, which is free to access for 4 weeks.

Synthesis, structure and unique reactivity of the ethylzinc derivative of a bicyclic guanidine
Karolina Zelga, Michał Leszczyński, Iwona Justyniak, Arkadiusz Kornowicz, Maciej Cabaj, Andrew E. H. Wheatley and Janusz Lewiński
Dalton Trans., 2012, Advance Article
DOI: 10.1039/C2DT11959E

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Hot Communication: Magnesium MOF

Most metal organic frameworks are based on 3-d or 4-f elements such as Zn, Cu, Co, Ni and there are notably fewer containing lighter metals such as Li, Be, B, Mg, and Al. This Hot Communication by Pingyun Feng and Xianhui Bu et al. reports the first Mg-MOF example constructed from the [Mg33-OH)(CO2)6] trimer and opens up the possibility of further Mg-MOF systems.

The porous crystal shows relatively high H2 uptake (1.37% at 77 K and 1 atm) showing that Mg-MOF systems may have great potential. The applications of MOFs include gas storage, separation, purification and catalysis, undoubtedly developing these applications requires the design and improvement of new MOFs.

You can download this Dalton Transactions Hot Article below, which is free to access for 4 weeks.

Induction of trimeric [Mg3(OH)(CO2)6] in a porous framework by a desymmetrized tritopic ligand
Quanguo Zhai, Qipu Lin, Tao Wu, Shou-Tian Zheng, Xianhui Bu and Pingyun Feng
Dalton Trans., 2012, Advance Article
DOI: 10.1039/C2DT12215D

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HOT Article: Role of the activator in dimerization catalysis

Despite the fact that the catalytic activity of Cr and W imido complexes in ethylene dimerization processes has been studied by various authors, to date the analogous Mo catalysts have not been studied.  In this HOT article, Dyer et al. set out to fill this gap in our knowledge and several molybdenum bis(imido) complexes were tested for ethylene dimerization catalysis in combination with EtAlCl2, showing moderate activity when bulky aryl substituents at the imido ligand are employed. In contrast, when MeAlCl2 is used the activity of the catalyst decreases considerably. To understand the role of the activator in these processes the authors have determined the molecular structures of several complexes derived of the reaction of bis(imido) molybdenum compounds with different aluminium halide reagents.

Read more for FREE about the role of the activator in dimerization catalysis until 20th February 2012 at:

Application of molybdenum bis(imido) complexes in ethylene dimerisation catalysis
William R. H. Wright, Andrei S. Batsanov, Antonis M. Messinis, Judith A. K. Howard, Robert P. Tooze, Martin J. Hanton and Philip W. Dyer
Dalton Trans., 2012, Advance Article
DOI: 10.1039/C2DT12061E

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HOT Article: Metallocyclic mechanisms at work?

In this HOT article, several new Ti(IV) complexes bearing aryloxy or alkoxy ligands have been prepared and evaluated as catalysts for the oligomerization/polymerization of ethylene. Obviously, polyethylene is the major product but ethylene oligomers also result, ranging from dimers to higher oligomers. The results indicate a number of different active species are formed upon activation, with oligomers likely arising through a metallacyclic mechanism.

Read more about the possible mechanism for FREE until 20th February 2012 at:

Preparation and structures of aryloxy- and alkoxy-Ti(IV) complexes and their evaluation in ethylene oligomerisation and polymerisation
James A. Suttil, David S. McGuinness, Markus Pichler, Michael G. Gardiner, David H. Morgan and Stephen J. Evans
Dalton Trans., 2012, Advance Article
DOI: 10.1039/C2DT11737A

See also the authors previous work providing further evidence for metallocyclic mechanisms at work at:

J. A. Suttil, D. S. McGuinness and S. J. Evans, Dalton Trans., 2010, 39,
5278

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Gold(III) and porphyrins – magic together

The authors of this Dalton Transactions Hot Article show that gold(III) has two roles in reactions between gold(III) and porphyrins. The gold coordinates with porphyrins to make new complexes and can act as an effective catalyst in C-H activation which can be tuned through changing the anions, ligands and oxidants. Why not download the article now for free until the end of Feb to find out more……

Dual facet of gold(III) in the reactions of gold(III) and porphyrins
Hongbin Lv, Boyan Yang, Jing Jing, Yi Yu, Jing Zhang and Jun-Long Zhang
Dalton Trans., 2012, DOI: 10.1039/C2DT12280D

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Porous coordination polymers by grinding

In their recent Dalton Transactions Hot Article, Susumu Kitagawa and colleagues show that mechanochemical synthesis is a promising alternative method for the systematic and large-scale production of porous coordination polymers (PCPs).

Mechanochemistry involves the grinding of solids together to force them to react – no solvent needed. This is good news as mechanochemical methods can be cheaper, faster, greener and simpler than more conventional reaction process.

Read Kitagawa’s study for free until the 20th February:

Systematic mechanochemical preparation of a series of coordination pillared layer frameworks
Hirotoshi Sakamoto, Ryotaro Matsuda and Susumu Kitagawa
Dalton Trans., 2012, DOI: 10.1039/C2DT12012G

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Single Molecule Magnets in 2D

Single Molecule Magnets (SMMs) are transition metal clusters that show superparamagnetic behavior below the blocking temperature. The advantage of SMMs over other traditional magnets is that they can be soluble in organic solvents, can form crystalline structures and have a uniform size. It is also possible to modify their magnetic properties by altering the organic ligands surrounding the transition metal clusters. SMMs have potential applications in quantum computing and information storage.

Giannis Papaefstathiou et al have synthesized two new coordination polymers. They are both built from [Mn6] clusters and trimesate anions. However beacuase the base reaction blend is sensitive to reaction conditions, two different complexes were formed. The first coordination polymer is a 2D non-regular net which is held together by dative and hydrogen bonds. The second coordination polymer has a 2D regular structure and is held together only by dative bonds. Although different in structure, both polymers contain [Mn6] SMMs with S=4 ground states. Experiments have shown that there are both antiferromagentic and ferromagnetic interactions between the manganese ions.


To find out more read the
Daltons Transactions full paper
Two-dimensional frameworks built from Single-Molecule Magnets
Athanassios D. Katsenis, Ross Inglis, Alessandro Prescimone, Euan K. Brechin and Giannis S. Papaefstathiou
CrystEngComm, 2012, Advance Article
DOI: 10.1039/C2CE06536C

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Metal complexes as biomolecular probes

Kenneth Kam-Wing Lo

The rich photophysical properties of luminescent inorganic and organometallic transition metal complexes, such as their intense, long-lived, and environment-sensitive emission, make them excellent candidates for biological and cellular probes. In this Dalton Transactions Perspective, Ken Lo and colleagues review examples of biological probes derived from luminescent transition metal complexes with a d6, d8, or d10 metal center.  Also discussed is the possible use of luminescent transition metal complexes as photodynamic therapeutics for various diseases or even light-activated drug release moelcules.

Applications of luminescent inorganic and organometallic transition metal complexes as biomolecular and cellular probes
Kenneth Kam-Wing Lo, Alex Wing-Tat Choi and Wendell Ho-Tin Law
Dalton Trans., 2012, DOI: 10.1039/C2DT11892

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Catalytic MOFs in a Click!

Metal Organic Frameworks (MOFs) have received a great deal of attention over the past fifteen years and have proved applicable in a variety of areas including gas storage, catalysis, gas purification and drug delivery. For catalysis, MOFs have been reported that can catalyze a range of organic transformations. By modifying the internal structure of  MOFs that allow them to interact with guest species, their chemical reactivity can be fine tuned.

In this article Marie Savonnet et al. have post synthetically modified MOFs by using “click chemistry” for application in base catalysis. Basic catalyltic amino centres and lipophillic phenyl groups were successfully introduced into the  DMOF parent structure. These new functionalized MOFs are able to catalyse the transesterification of ethyldecanoate in methanol with good performance. The substrates were co-adsorbed into the MOF structure and from the presence of basic amino groups in the internal MOF structure, methanol can be activated for nucleophillic attack of the ethyldecanoate carbonyl group. This paper demonstrates that through rational design, MOF catalysts can be engineered with appropriate pore size and functionalities for a particular application.

To find out more about this Dalton Transactions Hot Article read the full paper

Tailoring metal-organic framework catalysts by click chemistry
Marie Savonnet, Aurélie Camarata, Jerome Canivet, Delphine Bazer-Bachi, Nicolas Bats, Vincent Lecocq, Catherine Pinel and David Farrusseng
Dalton Trans., 2012, Advance Article
DOI: 10.1039/C2DT11994C

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