Shape-selective intercalation reactions

Cao, G. and Mallouk, T.E., Shape-Selective Intercalation Reactions of Layered Zinc and Cobalt... 

Somewhat surprisingly, intercalation reactions of certain layered double hydroxides show shape selectivity. For example, a strong preference for 1,5-naphthalenedisulfonate over 2,6-naphthalenedisulfonate is found on intercalation of an equimolar mixture into [EiAl2(0H)6]Cl H20 at 100 °C. Perhaps even more remarkably, the rate of intercalation into [Mgo.7Alo.3(OH)2](Cl)o.3nH20 of L-histidine was shown to... 

It has been also reported that the layer silicate intercalates can undergo an organic solid-state reaction within the interlayer region, such a reaction can be considered as highly regiospecific due to the distinct surface properties such as surface acidity or layer charge [5-7]. Moreover, size- and shape-selective layer silicates have been prepared [8,9] and the catalytic properties investigated in recent years [10]. 

Zinc methylphosphonate intercalates aliphatic amines with no branching at the a-position, for example n- and o-butylamines the sec- and tert-butylamine isomers are excluded because of steric restriction by the mediylphosphonate group (13a). In the case of zinc phenylphosphonate (Hgure 2), access to the site vacated by the water molecule is sufficiently restricted that only ammonia is intercalated, and aliphatic amines are excluded (13b). The excellent shape-selectivity of these reactions suggests the possibility of making sensors for amines and ammonia from zinc phosphonates, provided the intercalation event can be transduced to an observable (electronic, optical, mechanical, etc.) signal. 

Geometric factors play a role in the catalytic processes on clays. Smectites, for example, consist of regular, parallel sheets. The size and swelling properties of the interlayer space determine the size and shape of the molecules intercalating between the layers, which will have an effect on the selectivity of the reaction. 

Zeolites are crystalline, microporous aluminosilicates with molecular-sized intracrystalline channels and cages. Guest molecules with molecular diameters smaller than zeolites (from 3 to 15 A) can enter the interior of zeoUte crystals (intercalation) giving rise to shape and size selective sorption and, consequently, highly selective reactions. 

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