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Diamond-type framework

Gas separation based on size/shape exclusion has been achieved in a relatively large number of small pore frameworks. The 3D diamond-type framework [Mn°3(HCOO)6], for example, selectively adsorbs H2 over N2 and Ar at 78K and CO2 over CH4 at 195 K. Uptakes of the excluded gases N2, Ar and CH4 are almost zero due to their inability... [Pg.22]

The NaTl-type structure is the prototype for Zintl phases, which are inter-metallic compounds which crystallize in typical non-metal crystal structures. Binary AB compounds LiAl, LiGa, Liln and Naln are both isoelectronic (isovalent) and isostructural with NaTl. In the Li2AlSi ternary compound, A1 and Si form a diamond-like framework, in which the octahedral vacant sites of the A1 sublattice are filled by Li atoms, as shown in Fig. 13.7.2(b). [Pg.496]

Some other types of macrocycle compounds have been synthesized using adamantane and its derivatives. Recently, a new class of cyclobisamides has been synthesized using adamantane derivatives, which shows the general profiles of amino acid (serine or cystine)-ether composites. They were shown to be efficient ion transporters (especially for Na+ ions) in the model membranes [159]. Another interesting family of compounds to which adamantane derivatives have been introduced in order to obtain cyclic frameworks is crown ethers [160]. The outstanding feature of these adamantane-bearing crown ethers (which are also called diamond crowns ) is that ot-amino acids can be incorporated into the adamantano-crown backbone [160]. This family of... [Pg.242]

Polymeric compounds with limited Si-Si units in which the polymeric character is due to other bond systems, have been described. Another series of polymeric compounds exists, in which the Si-Si bonds themselves are responsible for the polymeric state. The extreme case, when all four valencies of a silicon atom are bonded with Si atoms, produces metallic silicon with a diamond structure. Compounds of the type (SiX2) or (SiX) result when some valencies of each silicon atom are occupied by other atoms or groups. Only polymeric compounds (SiXj,) withy from 2 to 1 exist SiX3 yields disilanes, and compounds withy between 3 and 2 yield limited chains. The possible stoichiometric compositions SiX2 and SiX are sometimes found, but a non-stoichio-metric composition is more common, which is understandable in view of the irregular framework of the Si-Si structure. The formation of regular or irregular Si-Si structures of stoichiometric or non-stoichiometric composition will depend on the procedures used in preparation. [Pg.101]

The sp -bonded zeolite type structures are obtained from natural silica frameworks by substituting the silicon atoms with carbon and removal of oxygen. We demonstrate that considering n-type doping such structures [46-48] behave very much like diamond. A mid-gap state occurs after a substantial relaxation of the impurity which is localized on a nearby carbon atom. [Pg.275]

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. [Pg.278]


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