Sandwich-type arrangement

Figure 5.5. The formation of intramolecular excimers usually involves the folding of a flexible chain, and the displacement of the large chromophores into a sandwich-type arrangement necessitates a large reaction volume.

These structural features are maintained more or less by all the ionophores in their complexed forms. However, mention should also be made of exceptions to these general structural principles. Thus, in the case of some ionophores, cation complexes of other than 1 1 stoichiometry have also been described in which the formation of sandwich -type arrangements is favored... 

In earlier research by one of us pronounced orbital symmetry effect on intramolecular charge-transfer absorption and emission spectra were reported from studies on cyclophanes containing aromatic D/A pairs in a close-contact sandwich type arrangement. The pairs 12(5,5)/12(4,8) and 13(6,6)/13(3,8) epitomize the plethora of D/A cyclophanes investigated in these studies (see Fig. 9). 

The alkaline earth metal cations with a large diameter (Sr, Ba ) and benzo-15-crown-5 stilbene derivatives are characterized by the formation of the 2 1 sandwich-type complexes (Scheme 10). In the case of Ba2+ the sandwich complex possesses the highest stability. According to the NMR studies and X-ray analysis of the sandwich complex of 8, molecules of dye are arranged in a head-to-head stacking. 

Open Structures (One-Dimensional Arrangement of Metal Atoms). An interesting sandwich type Structure (VI) with an MOs group and trigonal... 

Another approach for on-line degassing of solutions is to use a standard sandwich type gas-diffusion separator. One of the ports of the acceptor channel is blocked and the other connected to a vacuum source or to a pump which evacuates the gas from the channel. Such an arrangement was used by Hinkamp and Schwedt [13] in the determination of total phosphorus in waters with amperometric detection to remove gas bubbles generated in the reaction stream after an on-line continuous digestion in a microwave oven. 

The presence of a guest may also induce the face-to-face arrangement of porphyrins, thus leading to sandwich-type structures. This design bears much resemblance to the self-assembly approach. The two next examples illustrate potential developments in this field. 

Synthesis of sandwich-type metal phosphide with two P5 rings Discovered telomeres arranged themselves into 4-stranded G quadruplexes First synthetic virus created... 

The synthesis of the allyl-osmium complex [OsCl(Mes)(Ti3-2-MeC3H4)] has been reported and the compound shown by X-ray crystallography to have a half-sandwich type structure with an exo-arrangement of the methallyl ligand. 

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