Nitrobenzene guest molecules

In the crystal structure of [Ag C(4-C6H4CN)4 ]BF4 xPhNCh, the structural unit is of the hexamethylenetetramine type (Fig. 20.4.7). The nodes are Ag atoms and C(4-C6H4CN)4 molecules, and the rods are CN- -Ag coordination bonds. The void space is filled by the nitrobenzene guest molecules and BFJ ions. 

Figure 7.4 5 Immersing sublimed crystals of the apparently guest-free po phase of p-t-butylca 1 ix [4] arene results in the immediate displacement of bubbles of air from the crystal lattice as the air molecules are replaced by nitrobenzene guest (reproduced by permission of The Society of Chemistry).

The precise mix of free and occupied space inside the reactant filled container, the shape of the inner phase, the rigidity of the container and the electronic nature of its inner surface may all or in part contribute to the reaction dynamics and selectivity of an inner phase reaction. Reversible conformational changes of guest molecules are easily tractable spectroscopically and ideal to study the effect of confinement on transition states. Cram and co-workers studied the cis-trans isomerization of (CH3)2NCHO and (CH3)2NCOCH3 inside 5. For (CH3)2NCHO, the C—N rotational barrier deaeased in the order liquid phase > inner phase > vacuum and was 1 kcalmoT lower inside 5 than in nitrobenzene. For (CH3)2NC0CH3, the order was inner phase > liquid phase > vacuum and the barrier... 

Many calixarenes form complexes in the solid state, this property having been observed even before the structure of compounds was established. Among the simple ca-lix[n]arenes, for example, / >-rer/-butylcalix[4]arene forms complexes with chloroform, benzene, toluene, xylene, nitrobenzene, nitromethane, acetonitrile, and many others, while /r-rer/-butylcalix[5]arene complexes were studied with lower alcohols, ethyl acetate, toluene, and tetraline. More flexible / -terr-butylcalix[6]arene was found to form complexes with acetonitrile and / -rerr-butylcalix[8]arene with chloroform. The tenacity with which the guest molecule is held by the calixarene hosts varies widely with the size of macrocycle. Whereas tetramers to hex-... 

An example is found in the compound [3,3 5, 3" 5",3" -quaterpyridine(Cu2l2)] 2G, where G is the guest molecule, either nitrobenzene or cyanobenzene, see Figure 6.22. Apparently the 3D net is templated by these inclusion molecules as a guest free preparation results in a 2D-net [30]. 

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