Octahedral lithium

Co by contrast is seen in Figures 3 and 4 to have high-energy barriers at both delithiated and partially lithiated compositions along either type of pathway Oh Td Oh or Oh Oh) into the Li/vacancy layer. Results of TM ion defect calculations at full lithiation, i.e., Xu = 1, which are not shown, indicate that both Co and Mn are prevented from entering the Li layer by the lack of octahedral lithium vacancies. 

Depending on various location. Lithium atoms have different coordi-native valences those placed in (8) tetrahedral interstices have CN=4, and those placed in (4) octahedral interstices have CN=6. Yet, the constancy coordination law imposes that the Bismuth atoms to have CN = (8.4 + 4.6)/4 = 14. Indeed, each atom of Bi is surrounded by eight tetrahedral Lithium atoms at a distance ayfi and by 6 octahedral Lithium atoms at a distance all (0.5 a). Coordination polyhedron of the Bismuth atom is the p5rramidal cube. 

Exposure of TiCl in ethyl, propyl, and butyl alcohols for four weeks results in the precipitation of green octahedral Ti(III) complexes. Similar products form on irradiating Ti(OR)4 in ROH containing an equivalent of a lithium haUde (192). 

Table 4.3 indicates that octahedral coordination is a common mode for Li. Less usual is planar 6-fold coordination (Fig. 4.8a), pentagonal pyramidal coordination (Fig. 4.8i) or irregular 6-fold coordination (Fig. 4.9a). Examples of 7-fold coordination are in Fig. 4.9b and c. Lithium has cubic 8-fold coordination in the metallic form and in several of its alloys with metals of large radius. It is also 8-coordinate in the dilithionaphthalene complex shown in Fig. 4.9d here the aromatic... 

According to the above classification, the structures of LiNb(Ta)F6 and Li2Nb(Ta)OF5 should be composed of lithium cations and isolated octahedral complex ions, Nb(Ta)F6 or Nb(Ta)OF52, respectively. It is known, however, that the structure of these compounds consists only of octahedrons linked via their vertexes in the first case, and via their sides in the second case. The same behavior is observed in compounds containing bi- and trivalent metals. 

The type of crystal structure depends on the ratio X Me, where X is the total number of anions (oxygen and fluorine) and Me is the total number of all cations that can fit into/occupy octahedral voids (tantalum, niobium, lithium and other metals with similar ionic radii). 

In contrast, LiMn204 has a spinel structure. This material has the space group Fd3m in which the transition-metal and lithium ions are located at octahedral 8(a) and tetrahedral 16(d) sites, respectively, and the oxygen ions are at 32(e) sites. There are octahedral 16(c) sites around the 8(a) sites and lithium ions can diffuse through the 16(c) and 8(a) sites. As this structure contains a diffusion path for the lithium ions, these ions can be deinter-calated and intercalated in these compositions. 

Some cations with an octahedral-site preference (such as Ni2+, Co3+, and Cr3+) are expected to occupy the 16d sites of the spinel with Mn, whereas cations with a strong tetrahedral-site preference (such as Zn2+) are expected to occupy the 8a sites and to dislodge corresponding lithium ions into the 16d sites. In cases where Mn is substituted by transition metal ions (such as Co, Ni, and Cr) that can partake in the electrochemical reaction, voltage plateaus between 4 and 5V have been observed [135, 136],... 

It is worthwhile to point out that lithium extraction from inverse spinels V[LiM]04, such as V[LiNi]04 and V[LiCo]04 takes place at high voltage, typically between 4 and 5V [153]. Lithium is extracted from the octahedral 16d sites of these spinels with a concomitant oxidation of the divalent nickel or cobalt ions. From a structural point of view, this can be readily understood because lithium must be dislodged from the 16d octahedral sites, which are of low-energy, into neighboring energetically unfavorable 8b tetrahedra, which share all four faces with 16d sites that are occupied by nickel or cobalt and by lithium. Lithium extraction reactions... 

In a similar manner, treatment of anhydrous rare-earth chlorides with 3 equivalents of lithium 1,3-di-ferf-butylacetamidinate (prepared in situ from di-ferf-butylcarbodiimide and methyllithium) in THF at room temperature afforded LnlMeCfNBuOils (Ln = Y, La, Ce, Nd, Eu, Er, Lu) in 57-72% isolated yields. X-ray crystal structures of these complexes demonstrated monomeric formulations with distorted octahedral geometry about the lanthanide(III) ions (Figure 20, Ln = La). The new complexes are thermally stable at >300°C, and sublime... 

Balema, V.P., K.W. Dennis, and V.K. Pecharsky, Rapid solid-state transformation of tetrahedral [A1H4] into octahedral [A1H6]j in lithium aluminohydride, Chem. Commun., 17, 1665, 2000. 

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