Solid-state reactivity/topochemistry

Inclusion Reactions and Polymerization, p. 705 Preorganization and Complementarity, p. 1158 Secondary Bonding, p. 1215 Soft and Smart Materials, p. 1302 Solid-State Reactivity/Topochemistry, p. 1316 Strong Hydrogen Bonds, p. 1379... 

Based on some interesting reactions in certain inorganic crystalline compounds, Kohlschutter [9,10] proposed that the nature and properties of the products obtained take place on the surface or within the solid state. Indeed, he coined the term topochemistry for such reactions in the solid state. However, systematic investigations of photoinduced reactions in crystals began from 1964 onward by Schmidt and Cohen [11], Their studies on the 2tt + 2tt photoreaction of cinnamic acid derivatives in the crystalline state and correlation with the molecular organization in these crystals led to what are now known as Topochemical Principles. The most important conclusions reached by them are as follows (1) The necessary conditions for the reactions to take place are that the reactive double bonds are parallel to one another and the center-to-center distance be within 4.1 A (2) there is one-to-one correspondence between the stereochemistry of the photoproduct and the symmetry relationship between the reactants. The centrosymmet-ric relationship (called the a-form) leads to centrosymmetric cyclobutane (anti-HT), whereas the mirror symmetric arrangements (called the (5-form) produce mirror symmetric dimer (yy -HH). 

Recent work by Len MacGillivray of the University of Iowa, USA, has used topochemistry to produce an impressive range of new solid compounds by the addition of hydrogen bonded templates in order to bring about the designer orientations of photochemically reactive molecules in the solid state.34 A simple example is the use of resorcinol (1,3-dihydroxybenzene) to position two molecules of trans 1,2 bis (4-pyridyl) ethylene with their double bonds overlapping at ca. 4 A as required by the topochemical postulate. Upon photolysis the product rcfHetrakis(4-pyridyl)cyclobutane is formed stereospecifically and in 100 % yield, Scheme 8.2. In the absence of the resorcinol template trans-l,2-bis(4-pyridyl) ethylene is... 

The first systematic study concerning the relationship between the chemical reactivity of an organic solid and its crystal structure is generally associated with the work of Schmidt and his co-workers on the photodimerization of cinnamic acid and its derivatives. The main conclusions were summarized by Schmidt in 1971 and phrases such as topochemistry and crystal engineering were set to enter the lexicon of the organic solid state chemist. ... 

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