04.06.2010
РОССИЙСКАЯ АКАДЕМИЯ НАУК

УРАЛЬСКОЕ ОТДЕЛЕНИЕ

ИНСТИТУТ ХИМИИ TBEPДОГО ТЕЛА
   
| | | | |
| | | | | |
 04.06.2010   Карта сайта     Language По-русски По-английски
Новые материалы
Экология
Электротехника и обработка материалов
Медицина
Статистика публикаций


04.06.2010


Reactions in a crystal



02 June 2010



Crystals that can alter their composition without changing the structure of their solid lattice have been developed by US researchers. The crystals are made from an iridium complex bonded to dinitrogen (N2), but other gases such as hydrogen (H2) or ammonia (NH3) can diffuse through the lattice and undergo reactions. 


The crystals have great potential as novel reaction platforms, and can catalyse the hydrogenation of ethene gas (C2H4). Since larger molecules such as propene (C3H6) cannot enter the crystalline lattice, the process is highly selective. It is hoped that similar principles may be able to develop more size-selective crystals to perform industrially important reactions in the future. 


'When we first synthesised the iridium-nitrogen crystals, they were light red,' says Zheng Huang, who worked on the project at the Universityof North Carolina. 'After 12 hours in air they had turned dark-green, and analysis showed that oxygen had replaced the nitrogen.' 


'We found that the crystals would react with hydrogen to form Ir-H2-H2 and with ethene to form Ir-C2H4. This means it can carry out catalytic hydrogenation to ethane (C2H6), marking the first time a hydrogenation reaction has been carried out inside a crystal,' Huang adds.


Tunnelling gases


The secret lies in the composition of the crystals: iridium ions surrounded by large pincer-like ligands. The complicated ligands give the iridium high reactivity (allowing it to complex with nitrogen gas) but also leave voids in the crystalline lattice.


Stacking diagram of crystals









Stacking diagram of crystals - channels in the structure allow gases to pass through



© Nature



The voids act as tunnels, which small gases can use to traverse the structure. And although wide enough for molecules of carbon monoxide and ethene, the tunnels cannot accommodate the slightly larger molecules of carbon dioxide and propene.  


'This system seamlessly combines the benefits of homogenous catalysis (well defined reactive sites) with heterogenous catalysis (ease of separation),' says Timothy Warren at Georgetown University in Washington DC, US. 'By forcing substrates to migrate through the crystal lattice there is the potential for exquisite size and shape selectivity.'    


'This work clearly demonstrates the potential of achieving high selectivity using carefully-chosen crystal lattices,' says Malcolm Green of the University of Oxford, UK. However, he notes that designing customised crystals with useful applications in industry will still be challenging.  


'A close modification of this system could have different selectivities, but it is always difficult to predict how molecules will pack,' Green told Chemistry World. 'In addition, finding selectivity between industrially important compounds - such as pentene and hexene for example - will be more difficult due to their smaller relative difference in size.'


Lewis Brindley 


 


Interesting? Spread the word using the 'tools' menu on the left.



References


Z Huang, P S White and M Brookhart, Nature, DOI: 10.1038/nature09085


Дизайн и программирование N-Studio 
А Б В Г Д Е Ё Ж З И Й К Л М Н О П Р С Т У Ф Х Ц Ч Ш Щ Ъ Ы Ь Э Ю Я © 2004-2024 ИХТТ УрО РАН
беременность, мода, красота, здоровье, диеты, женский журнал, здоровье детей, здоровье ребенка, красота и здоровье, жизнь и здоровье, секреты красоты, воспитание ребенка рождение ребенка,пол ребенка,воспитание ребенка,ребенок дошкольного возраста, дети дошкольного возраста,грудной ребенок,обучение ребенка,родить ребенка,загадки для детей,здоровье ребенка,зачатие ребенка,второй ребенок,определение пола ребенка,будущий ребенок медицина, клиники и больницы, болезни, врач, лечение, доктор, наркология, спид, вич, алкоголизм православные знакомства, православный сайт творчeства, православные рассказы, плохие мысли, православные психологи рождение ребенка,пол ребенка,воспитание ребенка,ребенок дошкольного возраста, дети дошкольного возраста,грудной ребенок,обучение ребенка,родить ребенка,загадки для детей,здоровье ребенка,зачатие ребенка,второй ребенок,определение пола ребенка,будущий ребенок