Distorted polyhedra

A high internal phase liquid-liquid emulsion (HIPE) is one where the internal or dispersed phase droplets occupy >74% of the total volume of the emulsion. At this point the droplets contact each other and beyond this volume % the droplets are forced into distorted polyhedra. If for example styrene and divinylbenzene are employed as the continuous phase and water droplets dispersed in this oil phase using a suitable surfactant to form a HIPE, the comonomers can be polymerized to form a poly(styrene-divinylbenzene) polyHIPE. Typically the water droplets are... 

The tetrahedral or tetrahedral-distorted polyhedra are preferable for azo-methine chelates with coordination number 4 and coordination unit MN4 (868, X = NR, M = Co, Ni, Cu) [100,130,134,135,141]. At the same time, there are some suggestions for complexes 868 (X = NTs), according to whether the penta- (CN= 5) or hexa-coordinated (CN = 6) structures (tetragonal pyramid, elongated octahedron, mono- or two-capped tetrahedron) exist in them. The additional ligation of tetra-... 

Many ferroelectric materials were found in the past. However, there is a limited number of structures that are adopted by the majority of the commercially important ferroelectric materials. In each of these structures, the ferroelectricity is tied to distortion of the coordination polyhedra of one or more of the cations in the structure. One example is the perovskite structure. Cations that seem to be especially susceptible to forming such distorted polyhedra include Ti, Zr, Nb, Ta, and Hf. All of these ions lie near crossover points between the stability of different electronic orbitals, and so may be likely to form distorted coordination polyhedra [5], Polarizable cations such as Pb and Bi are also common to many ferroelectric materials. In this case, it has been suggested that the lone pair electrons may play an important role in stabilizing ferroelectric structures. Thus the ferroelectric transition temperature and spontaneous distortion of PbTiC>3 is much larger than that of BaTiC>3. 

Although these parameters serve as a test, comprehensive analysis is deemed necessary for a satisfactory way of distinguishing between distorted polyhedra. 

Intermediate and distorted polyhedra Near regular shape(s) Reference... 

The unique way in which the initial conversion is carried out is a matter of considerable scientific interest (79. 80) and leads to some practical consequences. Spheres are made to coalesce into distorted polyhedra until only microscopic traces of their original... 

Figure 3.12 lOH—Ba Ru Nafi. (a) The high-temperature structure (b) octahedral coordination polyhedra of Na and Ru above 823 K (c) distorted polyhedra at 298 K... 

G and E denote guest and host atoms, correspondingly. G — guest atoms situated inside pentagonal dodecahedra, G , G , and G — guest atoms situated inside larger 24-, 26-, and 28-vertex polyhedra Distorted polyhedra... 

More importantly, there are a number of cases where distorted polyhedra are formed around cations for electronic reasons. Chief among these are (a) transition metal atoms and (b) lone pair atoms. Each of these cases is briefly discussed. 

It should be mentioned that the two basic polyhedra are very closely related and only a very small spatial rearrangement is necessary to interconvert them. This means that it is often a difficult matter to decide which idealized geometry affords the more appropriate description. There have been attempts to define parameters in such a way that it will be possible to decide which is the appropriate polyhedron (Lippard and Russ, 1968). However, these are in reality only rejection tests and it is necessary to carry out a comprehensive analysis to arrive at a satisfactory assignment in cases of distorted polyhedra (Penneman et al., 1973). Only rarely has this analysis actually been carried out. 

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