Structures anti-layer

It has the anti-CdI2 structure, with alternating double layers of silver and intercalated fluorides. It is a metallic conductor. 

The occurence of the magnetic structure of the A-type also demands a 3-dimensional linking of octahedra in corners. The magnetic coupling, however, is of a different kind in the 3 directions The A-type is a magnetic layer structure, in which ferromagnetic sheets are coupled anti-ferromagnetically in the third direction. 

The CdCl2 structure is found for the chlorides of Mg, Mn, Co, Ni, and Zn the bromides of Ni and Zn the iodides of Ni, Zn and Pb. It is interesting that CS2O has the anti-CdCl2 structure, with the roles of the ions reversed. Here the polarization of the large Cs+ ions by O2- ions permits packing of adjacent Cs layers without anions between them. 

Cr20 is a rare example of the anti-CdI2 structure with adjacent layers of Cs+, the high polarisability of Cs+ ion must be a contributing factor. 

Initially, Byk Gulden s anti-ulcer investigations concentrated on the development of antacids. In 1957 [14,15], Byk Gulden invented the antacid magaldrate (Rio-pan ). This compound consists of a hydrotalcite-like layered structure, which shows a rapid partial neutralization of the acid to pH 4.0-4.5 and a strong addi-... 

Fig. 7a-d. Idealised lepresentations of various layer types observed in non-commensurate layer structures (a) octahedral layer, MX2, (111) B1 type (b) galena-like half octahedral (square pyramidal) layer, MX, (100) B1 type (c) the valleriite-like tetrahedral layer, MX, (111) anti-C 1 type (d) the mackinawite-like tetrahedral layer, MX, (100) anti-Cl type... 

TI2O is a variant of the anti-Cdl2 structure, which is the HCP counterpart to the anti-CdCl2 structure discussed in connection with CS2O (Section 3.2.2). For the thallium compound, there is a 12 layer stacking sequence in which the lone pair plays an important role. 

Other possible structures with 4-layer repeat units (AABB) namely, AcA BcB and AbA BcB. One is the structure of one form (hexagonal) of NbS2 the anti-NbS2 structure is adopted by Hf2S. No example of the other structure is known. It may interest the reader to check that there are only two structures with a repeat unit consisting of three pairs of layers, namely. 

The following compounds crystallize with one or other of the anti-Cdl2 or anti-CdCl2 structures i.e. structures in which non-metal atoms occupy octahedral holes between layers of metal atoms ... 

Finite units, chains and layers bonded together by m-m bonds anti chain and layer structures. 

By analogy with the normal layer structures (large polarizable anions) we should expect the anti structures to occur for the large polarizable cations such as Ag" ", Cs", Tl" , and Pb ". However, the situation is more complicated because not all these compounds are normal valence compounds there is clearly some delocalization of electrons in a number of them. It is interesting to compare the oxides of Cs ... 

The oxide TijO has a structure closely rdated to the anti-Bil3 layer structure which has been described in Chapter 4. 

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