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Lithium Cations (lithium + cation)
Selected AbstractsComplexes between Lithium Cation and Diphenylalkanes in the Gas Phase: The Pincer EffectCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2006Jean-François Gal Prof. Abstract The gas-phase lithium cation basicities (LCB values, Gibbs free energies of binding) of ,,,-diphenylalkanes Ph-(CH2)n -Ph (n=2, 3, or 7) and 1,1-diphenylethane Ph-CH(Me)-Ph were investigated by means of Fourier-transform ion cyclotron resonance (FTICR) mass spectrometry. Their structures, and those of the corresponding Li+ complexes were optimized at the B3LYP/6-31G(d) level and their relative stabilities calculated at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) level. Whereas the most stable conformers of the free diphenylalkanes were found to adopt a completely stretched aliphatic chain connecting the two benzene rings, the most stable Li+ complexes correspond to conformers in which the alkali metal cation interacts simultaneously with both benzene rings through the folding of the aliphatic chain ("pincer effect"). This chelation brings about a significant enhancement of the Li+ binding enthalpies (LBE values), which were calculated to be approximately 75 kJ,mol,1 higher than those evaluated for conventional (singly coordinated) , complexes in which the metal cation interacts with only one of the benzene rings. The increase of the corresponding lithium cation basicities, however, (Gibbs free energies of Li+ binding, LCB values) was calculated to be smaller by approximately 15 kJ,mol,1 as the pincer effect is entropically disfavored. The good agreement between the calculated LCB values, assuming a statistical distribution of the different conformers present in the gas phase, and the experimental LCB values measured by means of FTICR mass spectrometry are considered indirect evidence of the existence of the pincer effect. [source] Ligand-Exchange Processes on Solvated Lithium Cations: Acetonitrile and Hydrogen Cyanide,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2007Ewa Pasgreta Abstract Solutions of LiClO4 in solvent mixtures of acetonitrile and water, or acetonitrile and nitromethane, were studied by 7Li NMR spectroscopy. Measured chemical shifts indicate that the Li+ cation is coordinated by four acetonitrile molecules. In the binary water/acetonitrile mixture, water coordinates more strongly to Li+ than acetonitrile such that addition of water immediately leads to the formation of [Li(H2O)4]+. The solvent-exchange mechanism for [Li(L)4]+ (L = CH3CN and HCN) was studied by using DFT calculations (RB3LYP/6-311+G**). This process was found to follow a limiting associative mechanism involving the formation of relatively stable five-coordinate intermediates. The suggested mechanisms are discussed with reference to available experimental and theoretical data. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Electrophilic Attack on Sulfur,Sulfur Bonds: Coordination of Lithium Cations to Sulfur-Rich Molecules Studied by Ab Initio MO MethodsCHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2005Yana Steudel Dr. Abstract Complex formation between gaseous Li+ ions and sulfur-containing neutral ligands, such as H2S, Me2Sn (n = 1,5; Me = CH3) and various isomers of hexasulfur (S6), has been studied by ab initio MO calculations at the G3X(MP2) level of theory. Generally, the formation of LiSn heterocycles and clusters is preferred in these reactions. The binding energies of the cation in the 29 complexes investigated range from ,88 kJ,mol,1 for [H2SLi]+ to ,189 kJ,mol,1 for the most stable isomer of [Me2S5Li]+ which contains three-coordinate Li+. Of the various S6 ligands (chair, boat, prism, branched ring, and triplet chain structures), two isomeric complexes containing the S5S ligand have the highest binding energies (,163±1 kJ,mol,1). However, the global minimum structure of [LiS6]+ is of C3v symmetry with the six-membered S6 homocycle in the well-known chair conformation and three LiS bonds with a length of 256 pm (binding energy: ,134 kJ,mol,1). Relatively unstable isomers of S6 are stabilized by complex formation with Li+. The interaction between the cation and the S6 ligands is mainly attributed to ion,dipole attraction with a little charge transfer, except in cations containing the six sulfur atoms in the form of separated neutral S2, S3, or S4 units, as in [Li(S3)2]+ and [Li(S2)(S4)]+. In the two most stable isomers of the [LiS6]+ complexes, the number of SS bonds is at maximum and the coordination number of Li+ is either 3 or 4. A topological analysis of all investigated complexes revealed that the LiS bonds of lengths below 280 pm are characterized by a maximum electron-density path and closed-shell interaction. [source] Structural Studies of Lithium Telluro- and Seleno-Phosphorus CompoundsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2003Robert P. Davies Abstract Lithium tellurophosphinite [Ph2PTe][Li(TMEDA)1.33(THF)1.33] (4), ditellurophosphinate, [Ph2PTe2][Li(THF)3.5(TMEDA)0.25] (5), and selenotellurophosphinate [Ph2P(Se)Te][Li(THF)2(TMEDA)] (6) complexes have been prepared from the insertion/oxidation reactions of lithiated secondary phosphanes with elemental chalcogens and characterised by X-ray crystallography. Compounds 4,6 contain no tellurium,lithium bonding interactions in the solid state, instead existing as ion-separated species with THF/TMEDA-solvated lithium cations. Reaction of dilithiated primary phosphanes with more than three equivalents of elemental selenium gives [{(c -C6H11)P(Se)(SeLi)}2·2TMEDA] (7) via a phosphorus-phosphorus coupling reaction. Solid state characterisation of 7 reveals the organo groups in the tetradentate tetraselenohypodisphosphinate ligand to be in an anti conformation to one another and each lithium atom to be coordinated by two selenium atoms, one from each of the diselenophosphinate groups. Multinuclear NMR spectroscopic data are consistent with retention of the solid-state structures of 4,7 in solution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Physical and Electrochemical Properties of PVdF-HFP/SiO2 -Based Polymer Electrolytes Prepared Using Dimethyl Acetamide Solvent and Water Non-SolventMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 8 2007Kwang Man Kim Abstract Poly[(vinylidene fluoride)- co -hexafluoropropylene]/SiO2 polymer electrolytes were prepared by a phase inversion technique using DMAc solvent and water non-solvent. Cast film electrolytes filled with the same amount of SiO2 using DMAc were also made to compare physical and electrochemical properties. DMAc had a higher solubility to PVdF-based polymers than NMP, and DMAc produced highly porous structures with bigger cavities and influenced the reduction of crystallinity. Due to the highly porous nature of phase inversion membranes, the uptake of electrolyte solution reached more than 400% and room-temperature ionic conductivity was more than 10,3 S,·,cm,1. All of the liquid absorbed, however, did not necessarily contribute to increases in ionic conductivity. This was due to the different conduction modes of lithium cations in a complicated porous structure. Comprehensively optimizing all the properties measured, the phase inversion membrane electrolytes with 10,30 wt.-% SiO2 were the best candidates for use as the polymer electrolyte of lithium rechargeable batteries. [source] | ||||||||||