Guest solvation

It may be instructive to consider some examples of solvate formation. The compound 5-methoxysulphadiazine forms 1 1 host-guest solvates with dioxane, chloroform, and tetrahydrofuran [78]. These were prepared by heating to boiling a solution of the sulfonamide in the appropriate solvent, followed by slow cooling to obtain large crystals. Spironolactone forms 1 1 solvates with methanol, ethanol, ethyl acetate, and benzene. It also forms a 2 1 spironolactone-acetonitrile solvate [79,80]. The spironolactone solvates were prepared by crystallization in a refrigerator from solutions that were nearly saturated at room temperature. 

ENTHALPY-ENTROPY COMPENSATION AS A PRACTICAL TOOL FOR UNDERSTANDING AND ANALYZING GUEST SOLVATION AND MOLECULAR RECOGNITION... 

Enthalpy-Entropy Compensation as a Practical Tool for Understanding and Analyzing Guest Solvation and Molecular Recognition... 

Solvation is not simply an unavoidable passive event but rather plays essential active roles in supramolecular chemistry. Interaction of supramolecular host and guest with solvent, that is, host/guest solvation, critically affects the thermodynamics of supramolecular recognition. 

An enormous variety of solvates associated with many different kinds of compounds is reported in the literature. In most cases this aspect of the structure deserved little attention as it had no effect on other properties of the compound under investigation. Suitable examples include a dihydrate of a diphosphabieyclo[3.3.1]nonane derivative 29), benzene and chloroform solvates of crown ether complexes with alkyl-ammonium ions 30 54>, and acetonitrile (Fig. 4) and toluene (Fig. 5) solvates of organo-metallic derivatives of cyclotetraphosphazene 31. In most of these structures the solvent entities are rather loosely held in the lattice (as is reflected in relatively high thermal parameters of the corresponding atoms), and are classified as solvent of crystallization or a space filler 31a). However, if the geometric definition set at the outset is used to describe clathrates as crystalline solids in which guest molecules... 

Container molecules are of great interest because their encapsulated guests often exhibit novel and unusual properties, which are not observed in the free or solvated state (8,9). They are used today as probes of isolated molecules and of the intrinsic characteristics of the liquid state, and are capable of enantiose-lective recognition (10), reversible polymerization (11), isolation of reactive species (12-14), and promoting reactions within their interiors (15-18). For a valuable introduction to this area the reader is directed to some excellent review articles (15,19-21). 

In polar solvents with high donor numbers, the complex is solvated poorly relative to its separate components. This difference in solvation energies nullifies the hydrogen bonding interactions present in the complex, which, as a result, dissociates into its host and guest components. 

All of these interactions involve a host and a guest as well as their surroundings like solvation, crystal lattice, and gas phase. Electrostatic interactions are the driving force behind the ion pairing (ion-ion, ion-dipole, dipole-dipole, etc.) interactions, which are undeniably important in natural and supramolecular systems. The electrostatic interaction energy E is given by... 

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