Lithium halides, structure

In view of the facile oxidation of 10.13a-c it is not surprising that some metathetical reactions with metal halides result in redox behaviour. Interestingly, lithium halides disrupt the dimeric structures of 10.13a or 10.13c to give distorted cubes of the type 10.14, in which a molecule of the lithium halide is entrapped by a Ei2[E(N Bu)3] monomer. Similar structures are found for the MeEi, EiN3 and EiOCH=CH2 adducts of 10.13a. In the EiN3 adduct, the terminal... 

In the reactions of 10.13a with alkali metal terr-butoxides cage expansion occurs to give the sixteen-atom cluster 10.15, in which two molecules of MO Bu (M = Na, K) are inserted into the dimeric structure. The cluster 10.13a also undergoes transmetallation reactions with coinage metals. For example, the reactions with silver(I) or copper(I) halides produces complexes in which three of the ions are replaced by Ag" or Cu" ions and a molecule of lithium halide is incorporated in the cluster. ... 

The experimental values for the lithium halides are high. This is due to two different phenomena. In the case of the chloride, bromide and iodide the anions are in mutual contact, that is, the repulsive forces operative are those between the anions, and the anion radius alone determines the inter-atomic distances. The geometry of the sodium chloride structure requires that, for less than 0.414, the anions come into contact... 

The entrapment of lithium oxide and lithium halides by the lithium amidinate Li[Bu"C(NBu02] has been studied in detail by X-ray crystallography Interesting polycylic molecular structures have been obtained, as exemplified by the unusual sandwich complex of lithium oxide made from Li[Bu C(NBu )2l in toluene... 

Complex lithium halide spinels (Kanno, Takeda and Yamamoto, 1982 Lutz, Schmidt and Haeuseler, 1981), based on Li2CdCl4 and Li2MgCl4 have remarkably high Li ion conductivity for close packed structures. Fig. 2.11. These are complicated materials however, they have essentially inverse spinel structures but may exist also in various distorted forms. Some of them undergo a phase transition to defect rock salt structures at high temperatures some are non-stoichiometric. 

Experimentally, x values for gaseous lithium halides were determined as early as 1949 by molecular beam resonance experiments In solution, the quadrupolar interaction of ethyUithium and of t-butyllithium were investigated in 1964 . It was found that tetrameric and hexameric aggregates have different interactions. In the solid state x of tetrameric methyl- and ethyUithium was determined in 1965 and 1966 , and for lithium formate in 1972 . However, it was not untU Jackman started his investigations of lithium enolates and phenoxides in solution that the quadrupolar interaction was used in a systematic fashion to obtain structural information . 

More recent work has yielded another class of carborane-based mercury-containing macrocycles 43 and 44 related to crown ethers such as I2-crown-4 and 9-crown-3. Anticrown 43 associates with one or two moles of lithium halide, depending on conditions. The X-ray crystal structure of the chloride salt is shown in Figure 15. 

Crystal Structures of Lithium Halide and Mixed Lithium Halide -Organolithium Complexes... 

Fig. 25. Structures of selected lithium halide and lithium halide-organolithium complexes.

There are, however, other exceptions that are difficult to attribute to directional covalent bonds. The heavier lithium halides only marginally obey the rule, and perhaps a case couk) be made for C.N. — 4 for lil (Fig. 4.18). Much more serious, however, is the prohlcm of coordination number 6 versus 8- The relative lack of eight-coordinate structures—CsQ, CsBr, and Csl being the only known alkali metal examples—is commonly found, if hard to explain. There are no eight-coordinate... 

Structures of some lithium halide complexes (a) [fBu2Si(F)]2N Li 2THF, (b) [LiCl-HMPAL,... 

As anion-anion repulsion in a structure increases, it becomes easier to break down the ionic network in the solid and also to separate an aggregation of the ions into individual pairs. Such reasoning may be used to account for the trends in the data in Table 12-2, in which it is seen that the lithium halides and sodium iodide have abnormally low melting points and boiling points. The fluorides, for which anion-anion repulsion effects are less marked, are not listed. 

Structure 1 of oxaphosphetane is taken as proved. Ylid 5 or 4 as an intermediate stage on the way starting at educts R3P + Hal —CH2 —R was generated as a precursor of the structure 1 betaine 7, which is produced by fast splitting of oxaphosphetanes by for instance lithium halides [59] can be considered as a successor of the systeme 1 in the opposite direction to the olefin route. 

An eight-membered cyclic 7,./V-bis(germadiyl)bis(ketenimine) 190 was prepared by the reaction of tert-butyl-lithium with (fluorodimesitylgermyl)phenylacetonitrile 188 leading to the lithium salt 189, which then underwent an elimination of lithium halide. Compound 190, the first ring containing two ketenimine moieties, was characterized by IR and 13C NMR spectroscopy as well as X-ray structure determination (Scheme 34) <19980M1517>. 

Lithium halides when solvated show remarkable structural diversity.28 A simple one is [LiBr-Et20]4, which has a cubic L B core with OEt2 bound to the Li atoms, whereas [(LiCl)4-3.5tmeda]2 crystallizes as a bicyclic system of fused 6- and 4-... 

We have performed Xa calculations on the various lithium halide dimers, from which we have determined the sequence of molecular orbitals, their sjmnnetries and the energy span of the valence band. These calculations [summarized elsewhere (18)] are in reasonable agreement with experiment, and also Indicate that the dimers have a higher first I.P. than the monomers. The geometries chosen for these calculatians were the well-established planar-rhombic structures, with angles and distances taken from electron diffraction and infrared matrix isolation results. 

The structural information at an atomic level is essential for understanding the various properties of supercooled and glassy solutions. X-ray and neutron diffraction enables us to obtain direct structure information (bond distance and coordination number) of ionic solutions in terms of the radial distribution function. In the case of aqueous lithium halide solutions. X-ray diffraction data are dominated by halide-oxygen, halide-oxygen, and oxygen-oxygen interactions. On the contrary, neutron isotopic substitution... 

In the present study, we have made X-ray diffraction, neutron diffraction with isotopic substitution, and quasi-elastic neutron scattering measurements on highly concentrated aqueous solutions of lithium halides in a wide temperature range from room temperature to below glass transition temperature, from which the microscopic behaviors of the static structure and dynamic properties of the solutions are revealed with lowering temperature. The results obtained are discussed in connection with ice nucleation, anisotropic motion of water, crystallization, and the partial recovery of hydrogen bonds. 

Table 2. Important structural parameter values obteuned by least-squares fits for the aqueous lithium halide solutions at the various temperatures. T, r, b, and n are the temperature, the interatomic distance, the temperature factor, and the number of interactions, respectively. The values in parentheses are their estimated errors.

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