The dilithium molecule

The bond distance in gaseous L12 is Re = 267.3 pm, the dissociation energy is Do = 100 kJ mol Other spectroscopic parameters are listed in Table 4.1. 

The Lewis structure for this molecule would presumably be Li Li corresponding to a single, covalent bond. The strength of the bond is only a quarter of the strength of the bond in H2, presumably because of the larger size and more diffuse atomic orbitals on Li. 

The first reasonably accurate molecular orbital calculations published nearly 50 years ago [1] yielded the following MO for the two bonding electrons 

This MO may be rewritten as a linear combination of two hybrids, one at each atom. 

The ptos mixing ratio, 0.12, is so small that as a first approximation we may describe the bonding MO in Li2 as a combination of the 2 orbitals  

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The weakness of the covalent bond in dilithium is understandable in terms of the low effective nuclear charge, which allows the 2s orbital to be very diffuse. The addition of an electron to the lithium atom is exothermic only to the extent of 59.8 kJ mol-1, which indicates the weakness of the attraction for the extra electron. By comparison, the exother-micity of electron attachment to the fluorine atom is 333 kJ mol-1. The diffuseness of the 2s orbital of lithium is indicated by the large bond length (267 pm) in the dilithium molecule. The metal exists in the form of a body-centred cubic lattice in which the radius of the lithium atoms is 152 pm again a very high value, indicative of the low cohesiveness of the metallic structure. The metallic lattice is preferred to the diatomic molecule as the more stable state of lithium. 

For instance, GMCSC calculations on the boron anion [2] and on the dilithium molecule [26], both in their ground states, have shown how singleconfiguration wavefunctions, including spin-coupled ones, can be hard-put to provide a robust description of certain highly-symmetric systems. By robust description , we mean one that will not change, at least qualitatively, as more configurations are added to the wavefunction. 

The OBS-GMCSC method offers a practical approach to the calculation of multiconfiguration electronic wavefunctions that employ non-orthogonal orbitals. Use of simultaneously-optimized Slater-type basis functions enables high accuracy with limited-size basis sets, and ensures strict compliance with the virial theorem. OBS-GMCSC wavefunctions can yield compact and accurate descriptions of the electronic structures of atoms and molecules, while neatly solving symmetry-breaking problems, as illustrated by a brief review of previous results for the boron anion and the dilithium molecule, and by newly obtained results for BH3. 

The dilithium phosphandiide dimer 9 is complexed by two molecules of a fluorosilane. The complex crystallizes in the monoclinic space group P2i/n. The framework of the aggregate consists of a cen-... 

Another type of adducts [8, Eq. (3)] was formed by the reaction of di(fert-butyl)aluminum chloride with dilithium bis(trimethylsilyl)hydrazide in low yields below 30% [19]. The structure of 8 consists of a distorted heterocubane with four vertices occupied by nitrogen atoms, two of which are connected by an intact N—N bond across one face of the cube. The cation positions are occupied by two aluminum and two lithium atoms, of which the last ones bridge the N—bond. Part of the hydrazide molecules was cleaved, and the aluminum atoms are bonded to one ferf-butyl group only. On the basis of the NMR spectroscopic characterization many unknown by-products were formed in the course of that reaction, and no information is available concerning the reaction mechanism. Compound 8 may be described as an adduct of dilithium bis(trimethylsilyl)hydrazide to a dimeric iminoalane containing a four-membered AI2N2 heterocycle. Further... 

The most important esters in connection with Li batteries are y-butyrolactone (BL) and methyl formate (MF). Li is apparently stable in both solvents due to passivation. Electrolysis of BL on noble metal electrodes produces a cyclic 0-keto ester anion which is a product of a nucleophilic reaction between a y-butyrolactone anion (produced by deprotonation in position a to the carbonyl) and another y-BL molecule. FTIR spectra measured from Li electrodes stored in y-BL indicate the formation of two major surface species the Li butyrate and the dilithium cyclic P-keto ester dianion. The identification of these products and related experimental work is described in detail in Refs. 150 and 189. Scheme 3 shows the reduction patterns of y-BL on lithium surfaces (also see product distribution in Table 3). In the presence of water, the LiOH formed on the Li surfaces due to H20 reduction attacks the y-BL nucleophilically to form derivatives of y-hydroxy butyrate as the major surface species [18] [e.g., LiO(CH2COOLi)]. We have evidence that y-BL may be nucleophilically attacked by surface Li20, thus forming LiO(CH2)3COOLi, which substitutes for part of the surface Li oxide [18]. MF is reduced on Li surfaces to form Li formate as the major surface species [4], LiOCH3, which is also an expected reduction product of MF on Li, was not detected as a major component in the surface films formed on Li surfaces in MF solutions [4], The reduction paths of MF on Li and their product analysis are presented in Scheme 3 and Table 3. 

If we combine the splitting schemes for the 2s and 2p orbitals, we can predict bond order in all of the diatomic molecules and ions composed of elements in the first complete row of the periodic table. Remember that only the valence orbitals of the atoms need be considered as we saw in the cases of lithium hydride and dilithium, the inner orbitals remain tightly bound and retain their localized atomic character. 

The reduction of 5-phenyldibenzoborole 39 was achieved by using excess of lithium powder in THF suspension at —78 °C. The dilithium salt 40 was isolated as a THF solvate with a variable number of THF molecules depending on experimental conditions (Equation 5) <20030M1266>. 

Different positions of the Li+ ions and the TMEDA molecules are also observed in the two phases of dilithium 1,2-diphenylbenzocyclobutadiene-diide TMEDA (181)138). The X-ray structure of phase I is shown in Fig. 3a. A,projection of 181-1 normal to the benzocyclobutadiene-diide rings is given in Fig. 3 b. One Li+ ion is below the four-membered ring, the other one sits on the other side of the dianion slightly outside the four-membered ring. The two TMEDA molecules attached to the Li+ ions are oriented more or less orthogonally to one another. 

We have predicted that Li2 is stable with respect to lithium atoms, so we might expect to be able to observe dilithium molecules. At room temperature, lithium is a metal, but if we heat lithium up sufficiently, we do indeed find Li2 molecules present in the vapour. From Figure 4.8 we can only draw conclusions about the relative stabilities of Li2(g) and Li(g). When we say that a particular molecule is stable with respect to the atoms from which it is made, you should bear in mind that it may not be stable with respect to other molecules or to solid forms of the element or compound. 

The first straight-chain A5,9 fatty acid to be synthesized was actually the (5Z,9Z)-5,9-hexacosadienoic acid [47]. The methodology developed by Djerassi et al. is shown in Fig. (17). This six-step synthesis started with the unusual controlled ozonolysis of one of the double bonds of (lZ,5Z)-l,5-cyclooctadiene to secure a 100% Z stereochemistry for what eventually was going to be the A9 double bond of the target molecule. Transformation of the product to the tosylated acetal, followed by Grignard coupling under dilithium tetrachlorocuprate catalysis afforded (Z)-4-heneicosenal, which after Wittig olefination with 4-carboxybutyltriphenylphosphonium bromide resulted in the desired A5,9... 

Lithium atoms Li2 and Lila are each coordinated to two THF molecules. The dilithium compound reacts with fluorosilanes in a molar ratio 1 2 to give disubstituted eight-membered rings Reactions in mole ratio 1 1 lead to the novel bicyclic systrem l,3,5,7-tetraaza-2,4,6,8,9-pentasilabicyclo[3.3.1]nonane. 

Two complexes containing a dilithiated stilbene fragment have been prepared and isolated from the reactions of 1,2-diphenylethane with N-chelated butyl-lithium reagents. " The molecular and crystal structures of these compounds, stilbene bis(lithium tetramethylethylenediamine) (Figure 4a) and stilbene bis(lithium pentamethyldiethylenetriamine) (Figure 4b), have been determined by X-ray diffraction techniques. Each structure contains two amine-solvated Li atoms located above and below the olefinic bond of a stilbene molecule. The stilbene molecule is planar in both structures, and is in a trans configuration about the C(7)—C(7 ) bond, which is ca. 0.01 nm longer than that in trans-stilbene. " The optical and "C n.m.r. spectra of THF solutions of the related dilithium and disodium salts of tetraphenylethylene dianion, as well as the spectra of their mixtures, have been examined. " The data can be rationalized in terms of the... 

Conceptually, when two carbon-metal bonds are in the same molecule and in close proximity, these two carbon-metal moieties may exhibit novel reactivity. A few of 1,4-dilithio compounds are developed and used as 1,4-dianion precursors for the preparation of main group metaUole [22]. Besides, some dilithium or even polylithium compounds show interesting reactivity [7-21]. For example, bis (2-lithioallyl)amines [15], 2,9-dilithio-l,4,6,9-decatetraenes [16], 3,4-dilithio-... 

C09-0048. Molecules of dilithium can form in the gas phase at low pressure. Describe the bonding in L12 and include a picture of the overlapping orbitals. 

Dehydrobenzene or benzyne 158 can be trapped by all manner of species. 1,2-Dehydro-o-carborane 159 has been shown to undergo many of the same reactions as its two-dimensional relative, 1,2-dehydrobenzene. Although dehydroaromatic molecules can be formed in a variety of ways, synthetic pathways to 1,2-dehydro-o-carborane are quite limited. An effective procedure reported so far78 first forms the dianion by deprotonation of o-carborane with 2 equiv. of butyllithium. Precipitated dilithium carborane is then treated with 1 equiv. of bromine at 0°C to form the soluble bromo anion 160. Thermolysis of 160 with anthracene, furan, and thiophene as substrates leads to the adducts 161-164.79 80 1,2-Dehydro-o-carborane reacts with norbomadiene to give both homo 2+4 and 2+2 addition, leading to three products 165-167, in a 7 1 ratio79. An acyclic diene, 2,3-dimethyl-... 

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