Lithium structural models

Perhaps the most important chain configuration is the cis-, 4 structure favoured by reactions involving Li" counterion in non-polar solvents. In this instance a lithium compound modelling the active centre exists in both cis and trans forms in the ratio c/t, 35/65, and there seems no reason to suppose that... 

Pretsch, 1994 Xiao and Williams, 1994) uses genetic algorithms. These methodologies maintain a set of configurational states which are combined and retained or discarded on the basis of a variety of selection criteria. Genetic algorithm based optimization combined with an appropriate energy function has recently been shown to provide reasonable structural models and, indeed, permitted the structure solution from X-ray powder diffraction data of a novel lithium ruthenate compound (Bush et al., 1995), as described in Chapter 1. 

Figure 1.10. Structural model proposed for the lithium-polyacetylene complex. The unit cell is based on the space group Ric, and the dimensions are a = 12.4 A (o = 7.16 A) and c = 7.5 A. The distance in chain-axis projection between the lithium ion and the centre of the chain in projection is 2.15 A. (Reproduced from ref 94 with kind permission. Copyright (1989) American Physical Society.)...

Leung, K., Electronic Structure Modeling of Electrocheinical Reactions at Electrode/ Electrolyte Interfaces in Lithium Ion Batteries. J. Phys. Chem. C 2013,117, 1539-1547. 

Comparison of the quantum chemical calculations for electronic transitions for the structure modeling the interaction of LiCI(I)-l2-a-dextrin-peptide complex with the nucleotide triplet indicates that the DNA nucleotides can displace polypeptide and form stable complexes with molecular iodine and lithium halogenides. Interestingly, in such structures, molecular iodine binds both nucleotide triplet and lithium halogenides. 

It should be remembered that the structure is derived from neutron diffraction experiment and, as for all diffraction experiments, it represents a time-averaged summation through space of the contents of multiple unit cells. In the case of a fully ordered structure, such as that of room temperature phase of lithium phosphate, the averaging process is not apparent in the resulting structural model. However, in the case of... 

This structural model suggests that the limited lithium mobility that does occur in these compounds proceeds via a percolation pathway for lithium migration. This path is composed of portions of the material that contain either lithium cations or vacancies in the large interstitial void. The presence of a lanthanide cation in 55% of the subcells prevents the occupation of the immediately adjacent tetrahedrally coordinated lithium positions and so blocks the passage of Li. Thus the lithium conductivity in these structures will be limited first by the ability of lithium cations to exit the tetrahedrally coordinated site and secondly, by the availability of an empty interstitial site in an adjacent subcell. Given these limitations on ion movement through the structure, it would be surprising if these materials were fast lithium conductors. 

This structural model has features which can be seen to favour fast lithium ion conductivity, especially when compared with the relatively poorly conducting Nd and Pr analogues that contain tetrahedrally coordinated lithium. The presence of Li in pseudo square-planar coordination in Lio.5Lao.5Ti03 provides a large aperture for ion migration movement of the Li perpendicular to the plane defined by the four... 

In order to test this hypothesis and determine an appropriate structural model for solution-deriyed lithium borate networks (gels), Brinker et al. performed FTIR investigations of crystalline alkali borates and partially hydrated crystalline alkali-borates (with N4 = 0.25 to 0.50). A prominent spectral feature (see, e.g.. Fig. 37a) of the anhydrous tetra- and triborate compounds is the 1260-cm vibration due to oxygens bridging between trigonal borons contained in separate primary units [183] (Fig. 38a). Anhydrous lithium diborate is composed exclusively of diborate units linked by oxygens bridging between 3- and 4-coordinated borons and exhibits no 1260-cm vibration [185]. Partial hydrolysis of the tetra- (and triborates) causes a dramatic reduction in the relative intensity of the 1260-cm vibration (Fig. 37b). 

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