Host-guest networks

Most network structures are effective host structures for small guest molecules, often the solvent. Exceptions arise when there is a high degree of interpenetration, i.e. where two or more networks are entangled [7]. This type of host-guest behaviour is not intrinsic to the molecular components themselves, but occurs in cavities or clefts created by the assembly of the network structure. Mol-... 

The network structures to be discussed will all involved hydrogen bonding as the supramolecular synthon. It should be noted however that other interactions such as coordinate bonds and host-guest interactions may also organise host molecules into network structures. Coordination polymers constructed from molecular hosts may involve functionalised calixarenes [8-11], cyclotriveratrylene [12], or cucurbituril [13]. Calixarenes have also been used to build up network structures via host-guest interactions [14,15]. It is also notable that volatile species may be trapped within the solid state lattice of calix[4] arene with a structure entirely composed of van der Waals interactions [16]. 

Clathrates are the original host-guest compounds with chlorine clathrate hydrate - a compounds in which a water hydrogen bonded network hosts a molecule of Cl2 - being known since 1810. 

The importance of host-guest interactions in the predictable formation of open square grid networks was further exemplified with the reaction of Ni(N03)2 or Cu(N03)2 and ligand 8 in the presence of benzene [21]. With Ni(N03)2 it formed a doubly interpenetrated network as the anthracene moiety prefers to interact with itself rather than with benzene (Figure 9). With Cu(N03)2 it failed to form a 2D network but formed two types of one-dimensional chains. 

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