Hexagonal lattice hosts

Reversibility of hydrogen charging was very good at room temperature. This is because the hexagonal lattice of the metal host, like this of LaNi, does not undergo major transformation as hydrogen is inserted interstitially. This was the first AB -type interstitial hydride in which hydrogen is stored between metal atoms. 

Taken together, Steps A and B of this procedure describe the most expedient, large scale approach to 9-n-butyl-1,2,3,4,5,6,7,8-octahydroacridine, which is prepared in about 60% overall yield from inexpensive starting materials. This heterocycle is an important building block for hexagonal lattice receptors, which are relatively rigid, planar hosts for metal ions and organic molecules.2... 

One important host molecule among the inclusion compounds is urea. Ordinary crystalline urea is tetragonal, but when a guest is present, urea crystallizes in a hexagonal lattice, containing the guest in long channels (Fig. 3.1). ... 

Fig. 7 A High-resolution in-situ STM image of the hexagonal honeycomb phase Ila of TMA on Au(lll) 0.05 M H2SO4 in the presence of 3 mM TMA, Es=- 0.10 V, fx = 70 pA. The primitive unit cell is indicated. B TMA guest molecule positioned in the center of a honeycomb-type hexagonal TMA host lattice, Es=- 0.10 V, ix = 70 pA. C Proposed packing model of TMA in Ila. The unit cell and a centro-symmetric dimer motif are indicated. The parameters of the unit cell are summarized in Table 1 [67]...

MacNicol et al. have stressed the fact that trigonal symmetry is a constitutional feature common to several important hosts. A notable fact is that trigonal (or hexagonal) lattice symmetry is often preserved in spite of local conformational distortion of the component host molecules. On the basis of relevant structural analogies in relation with the preceding symmetry considerations it has been... 

Assembly of Linear Polymers with Hosts, Fabricating Hexagonal Lattices 165... 

The occlusion of a variety of molecules within tunnels of dathrate system derived from tri(o-phenylenedioxy) cyclotri-phosphazene (TPDCTP) was reported.Crystalline produa with following formula forms tunnels with hexagonal lattice, and was used as a host for a set of vinyl monomers. 

Yet another type of canal structure has been reported for the urea inclusion compound of 1,4-dichlorobutane 51). Even though the canals are pseudo-hexagonal in dimension, there is a significant difference in their symmetry. The host lattice is orthorhombic, space group Pbcn. The difference lies in the directions of the six pseudo-3j helices of host molecules around the walls of each canal the sequence is cyc/o-RRRLLL, as opposed to cyc/o-RRRRRR in the hexagonal inclusion compounds and cvc/o-RLRLRL in the rhombohedral. This orthorhombic host structure probably occurs also in the urea inclusion compounds with 1,5-dichloropentane and 1,6-dibromohexane 51). 

The structure of alumina on NiAl(l 1 0) was the subject of a surface X-ray diffraction study by Stierle et al. [46]. The model derived by Stierle et al. from the analysis of the X-ray diffraction data was based on a strongly distorted double layer of hexagonal oxygen ions, where the Al ions are hosted with equal probability on octahedral- and tetrahedral-coordinated sites the resulting film structure was closely related to bulk k-A1203. An attractive feature of Stierle s model was that it provided a natural explanation of the domain structure of the alumina overlayer, which is induced by a periodic row matching between film and substrate lattices. However, as pointed out recently by Kresse et al. [47], this structure model has two bonds with... 

The host crystal of chrysoberyl has a hexagonal-close-packed structure. The space group is orthorhombic Pnma with four molecules per unit cell. The AP ions are octahedrally coordinated by the oxygen ions and occur in two not equivalent crystal field sites in the lattice. The AP" sites lying in the mirror-... 

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