Clathrate frameworks

With the exception of the clathrate framework model, all these hypotheses appear to be qualitatively consistent with the available X-ray diffraction data on liquid water. It is argued by some investigators, however, that there are still significant inconsistencies between the most sophisticated statistical thermodynamic models for liquid water and the most sophisticated X-ray and neutron diffraction measurements [734-736]. The interpretation of these data from different experiments, using the concept of pair-correlation functions, shows discrepancies that are considered significant in terms of the instrumental precision, and the definitive answer seems not yet available [737J. 

Brickenkamp CS, Panke D (1973) Polyhedral clathrate hydrates, XVII. Structure of the low melting hydrate of n-propylamine a novel clathration framework. J Chem Phys 58 5284-5295... 

Binary clathrates AgSn44 (A = Rb, Cs) provide an interesting example of a superstructure formation due to the ordering of vacancies within the clathrate framework [49, 70]. As it was pointed out earlier tin clathrates often exhibit vacancies in the framework for the electron precise composition, e.g. (A+),(4/7-Sn°)3g(3h-Sn-) gD2. Two vacancies in the four-bonded framework... 

Tin anionic clathrates exhibit low values of thermal conductivity in the range of 0.6-2 Wm K . This is lower than the values for anionic Si- and Ge-containing clathrates with similar framework compositions and the same cations. This indicates that clathrate framework atoms play an important role in the scattering of heat-carrying phonons. Thus, the frameworks with heavier Sn atoms scatter phonons more effectively. 

In contrast to the scarce knowledge on hardness and elastic properties of intermetallic clathrates, there is an enormous amount of data on Einstein and Debye temperatures available in the literature. The exceptional vibrational features of these cage compounds were extensively smdied in recent years and will be discussed in the frame of this work. Needless to say that DPT calculations of electron and phonon density of states, of thermoelectric properties and of elastic properties have greatly supported clathrate research. In this context attention should be drawn to a recent work of Karttunen et al. [29], who employed the Perdew-Burke-Emzerhof hybrid density functional with localized atomic basis sets composed of Gaussian-type functions, to calculate the elastic properties of 14 different types of clathrate frameworks (for elemental structures of C, Si, Ge, Sn) predicting bulk and Young s moduli comparing them with their diamond-like, dense so called ot-phases. 

Experimental results [9,11,14,16], obtained after article [3] had appeared, confirm the conclusion about hydrate structures stability only in the case, where the big (T,P,H) cavities are completely occupied. This all the more concerns the combined cavities. Thus, we can draw a conclusion of the clathrate frameworks lability (dynamic instability) rather than of their metastability in the absence of the guest. 

Clathrate frameworks. The principal clathrate frameworks have a comparatively small set of polyhedra (cages D,T,P,H) in various combinations and with various degrees of distortion. A certain guest stabilizes the framework, whose cage geometry and their arrangement correspond to... 

It is common knowledge, that even one and the s-ame NiBi+X2 complex can give different clathrate frameworks [10] depending on the guest (B,... 

Allokiric solutions are formed in H2O - Buf NA - Bu NB systems (where Bu N is tetra-n-butylammonium cation, A and B are single charged anions). These clathrate frameworks consist of water molecules and anions, the guest being organic cation. 

The conditions of the formation of the solution of such kind for channel inclusion compounds are simplified substantially and seem to be reduced to those of the formation of the individual clathrates, i.e. to the conformity of the guest molecules dimensions to the cross-section of the clathrate framework channel (for urea for thiourea 6,9-7j4A). 

Figure 6. The solubility isotherm in the hydroquinone - HCOOH - CH3CN system (a) b - the variation of the total (y) and the constituent degree of the clathrate framework filling (yi - for acetonitrile, y2 -formic acid).

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