Anion layers

Fig. 9.9 Structure of the compound Li8Zn2Ge3 (R3c hexagonal setting) with its lacunal Zn2Ge3 hexagon-based anionic layer.

Fig. 2 Packing diagram of the layered structure of kl-(BEDT-TTF)2Cu(CF3)4(TCE) (top). The packing motif of the BEDT-TTF electron donor molecules (lower left). The anion layer contains both disordered [Cu(CF3)4] anions and neutral TCE solvent molecules (lower right). In all cases, hydrogen atoms have been omitted for clarity...

Fig. 6 A view down the c-axis of the (BEDT-TTFlFe BgHjoC SE salt, illustrating the very thick anionic layers which result from the thiophene derivatized iron carborane anions. Hydrogen atoms and disordered thiophene groups have been omitted for clarity...

Fig. 7 The novel packing motif of a" -(BEDT-TTF)4([Fe(C5H4S03)2]-6H20. Regions containing a-type circled with a dotted line, while regions with P"-packing are highlighted with an oval (top). The anionic layer is characterized by an extensive hydrogen bonding network (dashed bonds) between water molecules and the sulfonate functionality of the anion...

Mixed Valence Compounds with Mixed TTF/Anion Layers... 

Finally, we discuss the effects of chalcogen (S to Se) substitution. Although in (EDS-TTF)2FeBr4 remarkably close Se---Br contacts exist between donor and anion layers, little magnetic exchange interaction exists between the magnetic anions. The molecular orbital calculation reveals that the contribution of Se 4p orbital to the HOMO of the EDS-TTF molecule is considerably smaller than the contribution of... 

The crystal structure of [Fe(Cp )2][Ni(bds)2], as the salts described in Sect. 3.4.1, consists of 2D layers composed of parallel type IVa chains, which are separated by anion layers [15]. Besides contacts involving H atoms, no other short contacts were found in the structure. Within the IVa chains, one of the Cp fragments of the cation sits above a C6 ring of the ligand, while the second one is displaced towards the center of the anion. For the first Cp the closest D+A interatomic separation (C C) exceeds dw by 8%, while for the second Cp the closest D+A contact (C—Se) exceeds c/w by 4%. The D+D+A chains are relatively isolated and the solvent is located on cavities between the chains. No close interionic interlayer distances were observed involving molecules in the D+D+A layers and the anion layers or between the anions in the anionic layers. 

The crystal structure of [Fe(Cp )2]2[Cu(dcdmp)2] consists of a parallel arrangement of type IVa chains [63]. Unlike the other compounds based on type of chains, (IV) chains, with the D+D+A2 repeat unit, for this salt the chains are neutral, and there are no anionic layers. Within the chains, the cations sit on top of the pirazine rings from the ligands of the anionic complexes, with a separation between the Cp and the pirazine rings of 3.576 A. Besides some short contacts involving H atoms, no other short contacts were observed in this compound and the chains are relatively isolated. 

Cl 6c +(u,u,u +m, + m, + m + w, + w, +m) w= This structure has a rhombohedral symmetry but is usually described in terms of a triple-volume hexagonal cell, which makes comparison with the idealized Cdl2 structure simpler. The idealized unit cell is adequate for the purposes of this book. In this representation the anion layers are in cubic closest packing. .. ABC ABC ABC... The metal and nonmetal stacking sequence is... 

In ternary oxides AMO3 the second class of structures arises when A and M are the same size and the size is suitable for octahedral co-ordination. These adopt structures in which both ions are 6-coordinate. An example is the lithium nio-bate structure, which contains hexagonally packed anion layers (Figure 11.6(d)). Surprisingly, no known fluoride adopts such a structure. 

Consider the available fluorine sites to be the lattice positions of a cubic, close-packed, two-dimensional lattice. These are the oxygen positions of a cubic, close-packed, oxygen lattice in the (111) type planes. Aluminum ions are situated below this two-dimensional anion layer. Suppose a fraction f of all the sites is randomly occupied by fluorine atoms the remaining sites are occupied by O with zero magnetic moment. 

Fig. 2.7 Structure of feroxyhyte. a) Hexagonal close packed anion layer with cations distributed over the interstices, b) Layers of edge-sharing octahedra. (a, b Stanjek, unpubl.)...

Manceau, A. Lanson, B. Schlegel, M.L. Harge, J.C. Musso, M. Eybert-Berard, L. Haze-marm, J.-L. Chateigner, D. Lamble, G.M. (2000) Quantitative Zn speciation in smelter-contaminated soils by EXAFS spectroscopy. Am. J. Sd. 300 289-343 Manceau, A. Nagy, K.L. Spadini, L. Ragnars-dottir, K.V. (2000 a) Influence of anionic layer structure of Fe-oxyhydroxides on the structure of Cd surface complexes. J. Colloid Interface Sd. 228 306-316... 

Fig. 11 a Side view of an anion layer sandwiched between cation layers viewed down along the crystallographic n-axis. b CH/n interactions between the aromatic groups in the ammonium cation layers for 1-naphthylmethylammonium ( , )-sorbate [82]... 

As already discussed in Chapter 1, this kind of mixed valence salt becomes conductive due to the transfer of one electron from two BEDT-TTF molecules to the anion layers. However, at the surface, the charge can become unbalanced, resulting is an incomplete CT. This leads to differentiated surface vs. bulk nesting vectors and to the existence of surface CDWs (Ishida et al, 1999). The Peierls transition has also been observed on the a -planes of single crystals of TTF-TCNQ with a variable temperature STM (Wang et al, 2003) and will be discussed in Section 6.1. 

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