CrystEngComm Blog

In a recent paper, Langford et al report the formation of three new molecular porous materials with tunable channels.  Tunability of the size and shape of the channels is important in the design of materials for gas sensing, guest exchange, catalysis and drug delivery.  Other important factors such as thermal and solvent stabilities are also good.

The new compounds are readily prepared from tin(IV) porphyrin phenolates. Their structures feature a one-dimensional hourglass-shaped channel lined with methyl groups.  The nature of the channel is readily varied by changing the methyl substitution of the phenolate component.  In this way, the pore radius can be varied from 3.1 Å to 4.5 Å (see diagram below, showing the three compounds down the crystallographic c axis with channels shown as orange spheres and phenolic methyl groups lining the channel shown in purple).

The compounds are robust compared to other molecular porous materials, thought to be due to a combination of stabilisation by hydrogen bonding and stacking of the aromatic groups.  In combination with the tunability, this suggests potential use for guest exchange or in small molecule capture applications and further investigation of this is ongoing.

For more information see the full paper at:

Supramolecular materials with robust and tunable channels constructed from tin(IV)porphyrin phenolates
Shuang Wang, Craig Forsyth and Steven J. Langford
CrystEngComm, 2015,17, 3060-3063

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

Nitrobenzene is an important industrial material used in the production of aniline, dyes, pharmaceuticals and explosives.  However, it is highly toxic, considered likely to be a human carcinogen and does not readily degrade so accurate sensing of nitrobenzene in the environment, even at very low concentrations, is required.

A new paper presents a Cd-based metal-organic framework (MOF) as a highly selective and efficient sensor of nitrobenzene.  The MOF is based on a new flexible ligand with aromatic character, chosen to complement nitrobenzene’s electron withdrawing character.  The ligand, 1,1-(1,4-phenylenebis(methylene))bis(1H-pyrazole-3,5-dicarboxylicacid) and a source of Cd react under hydrothermal conditions to form the new Cd-MOF.

This shows a fluorescence emission when excited at 297 nm which is quenched by the presence of nitrobenzene (see diagram below).

The suggested mechanism of quenching involves photoinduced electron transfer. Quenching is inversely related to the concentration of nitrobenzene and significant quenching occurs at concentrations as low as 50 ppm nitrobenzene. Thus, Cd-MOF is suggested as a sensitive, rapid probe for low concentrations of nitrobenzene.

For the full paper see:

A new Cd(II)-based metal–organic framework for highly sensitive fluorescence sensing of nitrobenzene

Yu-Pei Xia, Yun-Wu Li, Da-Cheng Li, Qing-Xia Yao, Yu-Chang Du and Jian-Min Dou

CrystEngComm, 2015, Advance Article
DOI: 10.1039/C5CE00162E

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

The physical form of a compound affects its properties – one need only look at the explosion of research about nanosized materials in recent years to see the dramatic effects that size and shape can have on behaviour. Metal foams and foils with nanoporous structure have large surface-to-volume ratios, which make them valuable in a range of applications. Recently, Ming Li and colleagues, based in Shanghai, have developed a simple one-pot hydrothermal route to nanoporous copper foils that self-assemble in relatively short reaction times.

The mild hydrothermal route uses readily available starting materials, and ethylene glycol is employed as a reducing agent in the reaction. After 6 hours at 200°C the blue emulsion is transformed to a copper foil, which detaches itself from the Teflon wall of the autoclave liner.

The foil is thoroughly characterised and has a uniform thickness of approximately 1.4 microns, as seen in the SEM image below. A nanoporous structure can also be seen, accounted for by a mechanism of initial formation of Cu branches, which join together to form the foil as the reaction progresses. A thin coating of copper oxide on the surface makes the foils stable in air.

The as-synthesised copper foil and a close-up SEM image are shown below.

All so far so interesting, but what can such films be used for? The visible absorbance is higher than that of commercially available copper films owing to the nanostructure present. This means it can be used as an active substrate for surface enhanced Raman scattering (SERS). These substrates need to absorb light via surface plasmon resonance, an effect commonly seen in coinage metals. However, gold and silver have been found to be too expensive and too unstable, respectively, so cooper provides a high-performing low cost alternative.

Other potential applications include use as electrodes in batteries, solar cells or displays, and the authors hope that the method is applicable for the creation of other metal foils.

Find the full article here:

One-pot preparation of thin nanoporous copper foils with enhanced light absorption and SERS properties
Ming Li, Yanjie Su, Jiang Zhao, Huijuan Geng, Jing Zhang, Liling Zhang, Chao Yang and Yafei Zhang
CrystEngComm, 2015, 17, 1296-1304
DOI: 10.1039/C4CE01967A

Rachel Coulter is currently working on a PhD at the University of Liverpool, investigating near-infrared absorbing materials. Her interests include solvothermal synthesis, optical applications of inorganic compounds and synthesis of nanoparticles. She received an MChem from the University of Edinburgh in 2011, which included an Erasmus year in Lille, France.

Some crystals can deform on exposure to UV or visible light as a photoreaction proceeds during which the reactant and product are both present. This causes internal strain, which can result in crystals bending, jumping or twisting. For a well-defined response to occur, control of crystal size and shape are vital. Micron-sized crystals (microcrystals) are more likely to exhibit the desired behaviour, as larger crystals may shatter owing to the internal stresses produced.

A new paper outlines a method for producing uniform microcrystals. This is demonstrated by the synthesis of (E)-3-(anthracen-9-yl)acrylic acid (9-AYAA) from its t-butyl ester analogue by tumble mixing with phosphoric acid and a surfactant (sodium dodecyl sulfate, SDS). The size and shape can be controlled by the reaction temperature, concentration of phosphoric acid and SDS, the ester concentration and the mixing method. The optimised reaction conditions produce uniform 9-AYAA microwires, which undergo coiling (during the photoreaction) and uncoiling (as the reaction reaches completion) on exposure to 475 nm light, as shown in the figure below.

The new method involves an in-situ chemical reaction (acid hydrolysis) followed by re-precipitation and can also be successfully used to produce 9-AA (9-anthraldehyde) microplates under similar conditions. The authors attribute the success of their syntheses to the slow growth of the products and conclude the strategy could be used to produce microcrystals of uniform size and shape in other systems.

For more details, see the full paper at:

Chemical reaction method for growing photomechanical organic microcrystals
Rabih O. Al-Kaysi, Lingyan Zhu, Maram Al-Haidar, Muhannah K. Al-Muhannah, Kheireddine El-Boubbou, Tarafah M. Hamdan and Christopher J. Bardeen
CrystEngComm, 2015, DOI: 10.1039/C4CE02387K

Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.