ICCOSS XX: Growing crystals in all shapes -and sizes
All good things come to an end… Among the many, and varied, aspects discussed at ICCOSS over the past few days, I wanted to bring your attention to halogen–halogen bonding, which seems to be becoming quite popular. When a halogen atom engages in such a bond, its charge distribution changes a little, leading to a ‘polar flattening’ of the atom. The more electronegative side of one atom naturally engages in a halogen–halogen bond with what has become the more electropositive side of the other. Can these interactions be relied on to assemble building blocks? Can they be tuned in a controllable manner by judicious choice of the halogen?
But the good old hydrogen bond was far from being left out. I enjoyed E. Arunan’s presentation about giving atoms a hydrogen bond radius. After all, covalent, ionic or van der Waals interactions have their covalent, ionic or van der Waals radii counterparts, so although by no means easy it may well be possible to do that for the hydrogen bond too.
Another exciting feature of the solid state is chirality – which turns out to be a lot more widespread that one might think. Bart Kahr had some surprising numbers for us: 8% of organic compounds naturally crystallise in a helical form, and about 25% can be made to do so! He showed a very nice movie of a crystal growing helically — but with an optical axis that moves during the growth process: twisting occurs at the tip, and at the same time the bulk untwists. This, he suggested, is probably associated with strains and stresses that are caused by the presence of an impurity.
From a theoretical perspective, R. Ramasesha showed us how he goes about modelling molecular materials for electronic applications – in a JACS paper from 1911 (very possibly the oldest paper cited at the conference) Moore and McCoy wrote that “it is possible to prepare composite metallic substances from non-metallic constituent elements”. This is exactly what organic electronics are.
But I’m not going to list all the topics discussed. Why not come and see for yourself at the next ICCOSS, held in Cardiff in July 2013!
I did want to mention the presentation by Hitoshi Kanazawa, Professor at Fukushima University, about 60 km from the Daichi nuclear power plant, who reported on the situation and how he and his group went around measuring radioactivity after the accident (this is not easy, as the values measured depend on where exactly you take the measurement, how far above the ground, the winds at that moment and so on). He also tried to find a way to rinse the radioisotopes but all attempts have so far remained unsuccessful. As we know, this accident has been a disaster, and sadly cleaning up will take for ever.
Hitoshi Kanazawa also had a very interesting poster – but I’ll refrain from telling you all about it, as the results are unpublished. I will only say that admiring some sample materials that he’d brought involved a syringe and a band aid, which certainly made for an enhanced poster experience.
And finally… for all of you out there who just love pretty crystals – I know it’s not just me – I have good news: our Ali Baba’s cave does exist. It is in Chihuahua State, Mexico – aptly named the Crystal Cave – connected to the NAICA mines. Dario Braga showed striking pictures throughout his presentation – these caves shelter crystals as big as trees! How did they form? You can find out at the website of the team of scientists and explorers who are studying – and protecting – these amazing crystals.
Anne Pichon (Associate Editor, Nature Chemistry)