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The curious case of plutonium

29 Nov 2012

Plutonium colloids

Even 70 years after its discovery, the behaviour of plutonium still remains something of an enigma. Now Swedish researchers have discovered that plutonium colloids shrink with age becoming very small (3–4 atoms) with a shortening of the average Pu–O bond and Pu⋯Pu distances, consistent with partial oxidation having occurred.

Two types of colloidal materials were studied: high-fired crystalline PuO₂, and freshly prepared Pu(IV) colloids. The structures of both types were determined by EXAFS at the beginning of the experiment and after controlled aging of up to five years. The results show that even freshly prepared Pu(IV) colloids are polynuclear nano clusters with PuO₂ structure, bringing new insight into the evolution of plutonium with time.

Photoluminescent DNA binder

20 Nov 2012

Upon DNA binding, a 15-fold turn-on in emission intensity occurs.

Stephen Lippard and colleagues at Massachusetts Institute of Technology have synthesised and characterised a platinum(II) complex bearing the tetradentate, β-diketiminate ligand ([Pt(BDIQQ)]Cl). Cytotoxic studies showed [Pt(BDIQQ)]Cl to have similar potency to cisplatin on cervical cancer (HeLa) cells, whereas on human lung carcinoma (A549) cells [Pt(BDIQQ)]Cl was four times more potent than cisplatin. The complex elicits a strong photoluminescent turn-on response upon DNA binding and it is hoped this will be useful for further cellular imaging studies.

Read the article now to find out more…

Photoluminescent DNA binding and cytotoxic activity of a platinum(II) complex bearing a tetradentate β-diketiminate ligand
Jennifer M. Hope, Justin J. Wilson and Stephen J. Lippard
Dalton Trans., 2013
DOI: 10.1039/C2DT32462H, Communication

Other Dalton Transactions articles by this author include:

A C2-symmetric, basic Fe(III) carboxylate complex derived from a novel triptycene-based chelating carboxylate ligand
Yang Li, Justin J. Wilson, Loi H. Do, Ulf-Peter Apfel and Stephen J. Lippard
Dalton Trans., 2012,41, 9272-9275
DOI: 10.1039/C2DT31260C, Communication

Non-traditional platinum compounds for improved accumulation, oral bioavailability, and tumor targeting
Katherine S. Lovejoy and Stephen J. Lippard
Dalton Trans., 2009, 10651-10659
DOI: 10.1039/B913896J, Perspective
From themed issue Metal anticancer compounds

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Homo- and heterogeneous photocatalytic water reduction

14 Nov 2012

With TONs up to 9000 H₂/Co this Hot Communication by Peter Hamm and Roger Alberto et al. is worth a read.

The team have developed a stable, water reducing catalyst which operates under acidic conditions and indicates poly-pyridyl ligand frameworks are superior to some of the other commonly used chelators. They also show the cobalt complex retains catalytic activity when resin bound, meaning it is active as both a homogeneous and heterogeneous catalyst. For full details download the article below.

A highly stable polypyridyl-based cobalt catalyst for homo- and heterogeneous photocatalytic water reduction
Miguel Guttentag, Alexander Rodenberg, Cyril Bachmann, Anna Senn, Peter Hamm and Roger Alberto
Dalton Trans., 2012, Advance Article

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Diphosphine ligand stabilisation of onion-like RuPt nanoparticles

30 Oct 2012

The catalytic potential of metal nanoparticles is widely understood and some are already used for heterogeneous catalysis. In a dedication to Professor Cole-Hamilton, Karine Philippot and Bruno Chaudret et al. report the synthesis and characterisation of uniquely stabilised RuPt nanoparticles.

A diphenylphospine was used to stabilise bimetallic RuPt nanoparticles, both decorating them and affecting their chemical composition. Neither an ordered alloy nor a core-shell structure was produced; instead, as proven by scattering and spectroscopic techniques, very disordered nanoparticles with Ru cores and alloy shells were observed. The mechanism that produces such an “onion” structure is thought to involve the reaction of the diphosphine ligands with Ru at the beginning of the reaction.

The use of reactive ligands in the synthesis of bimetallic nanoparticles can modify their structure, suggesting the possibility of finely tailoring the structure and surface of such nanoparticles in the future. These modifications have already shown promise, with CO poisoning of RuPt nanoparticles having much less of an effect on hydrogenation reactions than with analagous pure Ru examples.

To find out more about these new bimetallic nanoparticles, download this HOT article now.

On the influence of diphosphine ligands on the chemical order in small RuPt nanoparticles: combined structural and surface reactivity studies
Patricia Lara, Tuğçe Ayvalı, Marie-José Casanove, Pierre Lecante, Alvaro Mayoral, Pier-Francesco Fazzini, Karine Philippot and Bruno Chaudret

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Organic radicals in a self-assembled grid

26 Oct 2012

Konstantin Shuvaev, Annie K. Powell and colleagues have designed a ligand containing the nitronyl nitroxide radical. The ligand can self-assemble with copper(II) ions to give a [2 x 2] grid complex.

The nitronyl nitroxide radical coordinated via the oxo-atom of the N+-O- fragment in a chelating fashion and lies in the equatorial plane of the metal ion.

The high reactivity of organic radicals makes them difficult to use but the nitronyl nitroxide radical is one of the most stable and so can be used in the design of paramagnetic polytopic ligands as building blocks for supramolecular grids. Most previous supramolecular grids have been made using diamagnetic ligands but the team found that being able to use a paramagnetic ligand resulted in a grid with interesting spin coupling and magnetic properties.

CNC pincer ligand catalyst

18 Oct 2012

Scientists in Mexico and Spain have synthesised a ruthenium complex using a N-heterocyclic CNC pincer ligand.

Lutidine-derived pincer complexes are well established amongst organometallic chemists. More traditionally, the pincer ligand motif, PNX has been utilised (where P is a phosphine and X is either a phosphine or N donor ligand) but substitution of phosphines with stronger electron-donating N-heterocyclic carbenes has meant that more active catalytic species have been made for promoting hydrogenation of non-active esters. Mostly speaking, these ligands follow a CNN coordination pattern. According to the researchers, the only CNC pincer complex reported coordinates to the ruthenium centre in a mer geometry.

In their latest Dalton Transactions Communication, the team report on the synthesis of a CNC ligand which coordinates to ruthenium in an usual fac mode. They proved that the resultant complex can be used to catalyse the hydrogenation of imines by firstly deprotonating one of the ligand methylene bridges.

To read more about this development, read the full article now…

Hydrogenation of imines catalysed by ruthenium(II) complexes based on lutidine-derived CNC pincer ligands
Martín Hernández-Juárez, Mónica Vaquero, Eleuterio Álvarez, Verónica Salazar and Andrés Suárez
Dalton Trans., 2012, Advance Article

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Mononuclear Pacmans

09 Oct 2012

As Jason Love described in his 2009 ChemComm Feature Article, pyrrole-based macrocycles are ideal ligands for creating pre-organised metal binding sites to enable the multielectron redox chemistry so required for transforming small molecules such as O₂, carbon dioxide and water.

Here in their latest Dalton Transactions article, Love and colleagues take this a step further.

The team note how their previous attempts to make mononuclear transition metal complexes with the donor ligands were unsuccessful. Despite significant efforts, they could only make bimetallic complexes – well, until now that is…

The newest set of ligands now incorporate N₄^¬with either O₅ or ONO donors which are separated through aryl spacers. Upon binding of a singular metal atom, the complexes fold to form a Pacman-like cleft structure. Love and colleagues expect the structure to play host to guest molecules which can benefit from metal coordination as well as hydrogen bonding interactions to the oxygen and nitrogen atom acceptors.

To read more, download the article now…

Synthesis and structures of transition metal pacman complexes of heteroditopic Schiff-base pyrrole macrocycles
James W. Leeland, Colin Finn, Bérengère Escuyer, Hiroyuki Kawaguchi, Gary S. Nichol, Alexandra M. Z. Slawin and Jason B. Love

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Studying hydrogen activation of FLPs

04 Oct 2012

Scientists from Pacific Northwest National Laboratory have investigated the mechanism of heterolytic H₂ activation by frustrated lewis pairs (FLPs). To do this, they employed an unique approach of solution calorimetry and were able to obtain the enthalpies and relative rates of H₂ activation.

With the exception of previous studies that partly relied on theoretical calculations, there has not been a great deal of work devoted to understanding how molecular hydrogen is activated by FLPs. Autrey and colleagues have found that H₂ activation rates using such species are relatively fast considering no metals are involved. They discovered that the rate was dependent on the structure of the Lewis basic amine involved, and that diffusion of hydrogen across the gas-liquid interface is not rate limiting.

Further work is needed to extract fundamental rate constants, kinetic orders, and activation barriers, say the researchers.

Read the article now to find out more…
A thermodynamic and kinetic study of the heterolytic activation of hydrogen by frustrated borane–amine Lewis pairs
Abhi Karkamkar, Kshitij Parab, Donald M. Camaioni, Doinita Neiner, Herman Cho, Thomas K. Nielsen and Tom Autrey

This article is part of an upcoming themed issue on Boranes and Borohydrides, guest edited by Simon Aldridge. Other articles by this author include:

Methods to stabilize and destabilize ammonium borohydride
Thomas K. Nielsen, Abhi Karkamkar, Mark Bowden, Flemming Besenbacher, Torben R. Jensen and Tom Autrey

Also of interest… Take a look at our recent themed issue in Frustrated Lewis Pairs

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Group 4 tetracarbamato complexes for lactide polymerization

24 Sep 2012

Ever since Ziegler and Natta’s 1950s discovery of TiCl₄ as a catalytic precursor for alkene polymerization, interest in similar compounds with potentially superior properties has soared.

Biodegradable polylactic acid cups

Polylactide, polyglycolide and polycaprolactone are all commercially available biodegradable polyesters with advantages over non-biodegradable alternatives. They are used primarily in biomedical applications ranging from sutures, screws and pins to drug delivery and dentistry. Biodegradable polymers have also found uses in areas as diverse as compostable food packaging, plastics repair and rapid prototyping.

Marchetti et al. have reported a number of group 4 N,N-dialkylcarbamato complexes alongside their catalytic properties with regard to the ring opening polymerization of rac-lactide. They have also studied their polymerization mechanisms in great detail, concluding that the first stage of the polymerization reaction proceeds through different pathways for the Ti, Zr and Hf analogues, explaining the observed differences in activity. All pathways produce a vacant metal site, which is required for further propagation.

Read more about these new group 4 tetracarbamates and their application as catalytic precursors for the polymerization of rac-lactide in this HOT article.

Ring opening polymerization of rac-lactide by group 4 tetracarbamato complexes: activation, propagation and role of the metal
Fabio Marchetti, Guido Pampaloni, Calogero Pinzino, Filippo Renili, Timo Repo and Sirpa Vuorinen

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Ammonium borohydride – a promising hydrogen storage material?