And guest-host interactions

The term semi-clathrate refers to solid inclusion compounds where, in addition to non-bonded, clathrate interactions, there is a contribution of chemical bonding. In the example used above, this chemical contribution is of ionic nature fluoride anion from the ammonium salt is incorporated into the water host framework linked via hydrogen bonds. Thus, the host has anionic character and guest-host interactions have ionic component. 

Moreover, the empirical force field (EFF) calculations of the guest-guest and guest-host interaction energy were performed for different orientations of the guest molecules. 

Both guest-guest and guest-host interactions contribute to... 

Because the size regime of n=l-6 atoms is of great practical significance to the spectroscopic, chemical and catalytic properties of supported metal clusters in both weakly and strongly interacting environments (28), it is important to study very small metal clusters in various types of substrate as well as in the gas phase. In this way, one can hope to develop a scale of metal cluster-support effects (guest-host interactions) and evaluate the role that they play in diverse technological phenomena. 

One of the objectives of this paper is to evaluate the spectroscopic and photochemical consequences of the occurrence of markedly disparate guest-host interactions in the ground and optically excited states of Cu and Ag atoms, and some of their low nuclearity clusters, in rare gas as well as other supports. Original papers should be consulted for details. 

The observation of large Stokes shifts for the 2P-2S transition of entrapped Ag atoms indicates that the guest-host interactions are markedly different for the 2S and 2P states of this system and can be explained in terms of matrix cage relaxation effects. 

Studies of the energetics and dynamics of Cu2 and Ag2 in rare gas solids have also been completed (31,34). The absorption and fluorescence spectra are similarly indicative of strong guest-host interactions in the low lying states of Cu2 and Ag2 Rather than presenting the spectroscopic and photolytic details, a summary of the observed radiative relaxation processes of visible and uv excited Cu2 and Ag2 in rare gas solids is shown below ... 

The absorption and fluorescence spectra of Ag2 in rare gas solids are also clearly indicative of strong guest-host interactions involving the A1 and C1 Instates of Ag2 as summarized below ... 

From the above discussion, it should be possible to appreciate how extremely subtle differences in guest-host interactions in the ground and excited states of Cu and Ag atoms and dimers in both non-reactive and reactive supports can lead to dramatically distinct chemical reactivity patterns and dynamical processes. Photochemical and photophysical phenomena of this kind should provide chemists of the 21st century with a rich field for fundamental and applied research, offering considerable scope for experimental challenges and intellectual stimulation. 

GH Heilmeier and LA Zanoni, Guest-host interactions in nematic liquid crystals a new electrooptic effect, Appl. Phys. Lett., 13 91-92, 1968. 

Coordination causes electron-spin density redistribution in the N-O fragment the contribution of resonance structure II increase. The redistribution of spin density results in changes in the parallel component of the nitrogen hyperfine tensor. TEMPO and anthraquinone (AQ) have been used in this way to probe the Lewis acidity of alumina and Li and Mg doped alumina matrices.176 The differences in the Lewis acidic strength towards TEMPO and anthraquinone are discussed. An interesting study has appeared aimed to study the guest-host interaction between poly(amidoamine) dendrimers labelled with nitroxides and several porous solids including alumina.177... 

Although the answers to questions such as these depend on a complex array of factors ranging from the structure of the relevant molecules to their environment and the chemical activity of the medium containing the molecules, intermolecular (guest-host) interactions play a central role in determining the rate and the efficiency of the ultimate result. A major component of the many possible intermolecular forces is the electrostatic interaction, particularly because of the long-range nature of the Coulombic forces and the inevitable influence of the ionic atmospheres that surround the macromolecules and substrates. 

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