Quasimolecules in Compressed Lithium

Under high pressure, some materials form electrides, with valence electrons separated from all atoms and occupying interstitial regions. This is often accompanied by semiconducting or insulating behavior. The interstitial quasiatoms (ISQ) that characterize some high pressure electrides have been postulated to show some of the chemical features of atoms, including the potential of forming covalent bonds. It is argued that in the observed high‐pressure semiconducting Li phase (oC40, Aba2), an example of such quasimolecules is realized. The theoretical evaluation of electron density, electron localization function, Wannier orbitals, and bond indices forms the evidence for covalently bonded ISQ pairs in this material. The quasimolecule concept thus provides a simple chemical perspective on the unusual insulating behavior of such materials, complementing the physical picture previously presented where the global crystal symmetry of the system plays the major role.     

Raman and Infrared Spectroscopic Characterization of the Phosphate Mineral Lithiophilite—LiMnPO4

Abstract

The metal lithium is very important in industry, including lithium batteries. An important source of lithium besides continental brines is granitic pegmatites as in Australia. Lithiophilite is a lithium and manganese phosphate with chemical formula LiMnPO₄ and forms a solid solution with triphylite, its Fe analog, and belongs to the triphylite group that includes karenwebberite, natrophilite, and sicklerite. The mineral lithiophilite was characterized by chemical analysis and spectroscopic techniques. The chemical is: Li_1.01(Mn_0.60, Fe_0.41, Mg_0.01, Ca_0.01)(PO₄)_0.99 and corresponds to an intermediate member of the triphylite-lithiophilite series, with predominance of the lithiophilite member. The mineral lithiophilite is readily characterized by Raman and infrared spectroscopy.     

Sodium Borohydride–Solid LiClO4: An Effective Reagent for Reducing Aldehydes and Ketones in Aprotic Solvent

An efficient and simple method for the reduction of aldehydes, ketones and acid chlorides has been accomplished by using NaBH₄–solid LiClO₄ in mild conditions at ambient temperature with complete chemoselectivity in reduction of α,β‐unsaturated aldehydes and ketones. The reaction is fast with high yield and simple workup.     

Standard enthalpy of formation of lithium diphosphate

Lithium carbonate (Li₂CO₃) and ammonium dihydrogen phosphate (NH₄H₂PO₄) were used for synthesizing lithium diphosphate (Li₄P₂O₇). The purity of the latter compound was checked up by X-ray diffraction. The heat of dissolution of (Li₄P₂O₇) in phosphoric acid solution was measured in a C-80 SETARAM calorimeter. Many dilution and mixing processes in acid solutions of several concentrations (w/w) H₃PO_4, were also realized in the calorimeter in order to get the standard enthalpy of formation of this product. Two thermochemical cycles were investigated and the obtained values for the enthalpy of formation are: (−3383.4 and −3147) kJ · mol⁻¹. The former one is in better agreement with literature data.     

Synthesis of azafluorenones and related compounds using deprotocupration–aroylation followed by intramolecular direct arylation

The efficiency of the deprotocupration–aroylation of 2-chloropyridine using lithiocuprates prepared from CuX (X=Cl, Br) and LiTMP (TMP=2,2,6,6-tetramethylpiperidido, 2 equiv) was investigated. CuCl was identified as a more suitable copper source than CuBr for this purpose. Different diaryl ketones bearing a halogen at the 2 position of one of the aryl groups were synthesized in this way from azines and thiophenes. These were then involved in palladium-catalyzed ring closure: substrates underwent expected CH-activation-type arylation to afford fluorenone-type compounds, and were also subjected to cyclization reactions leading to xanthones, notably in the presence of oxygen-containing substituents or reagents.     

Asymmetric syntheses of dihydroxyhomoprolines via doubly diastereoselective lithium amide conjugate addition reactions

The asymmetric syntheses of novel dihydroxyhomoprolines have been achieved using the doubly diastereoselective conjugate additions of the antipodes of lithium N-benzyl-N-(α-methylbenzyl)amide to a set of four chiral α,β-unsaturated esters (derived from d-pentoses) as one of the key steps. A full account of the diastereoselectivity observed in these conjugate additions is presented and the stereochemical outcomes of these reactions have been established unambiguously via a combination of hydrogenolytic chemical correlation and single crystal X-ray diffraction analyses. A tandem hydrogenolysis/intramolecular reductive amination reaction was then used to create the corresponding enantiopure pyrrolidines, providing access to (2′S,3′S,4′R)-dihydroxyhomoproline and (2′S,3′R,4′S)-dihydroxyhomoproline after deprotection.     

The New Carbodiimide Li2Gd2Sr(CN2)5 Having a Crystal Structure Related to That of Gd2(CN2)3

The new carbodiimide compounds Li₂RE₂Sr(CN₂)₅ (RE = Sm, Gd, Eu, Tb) were prepared by a straight forward solid state metathesis reaction of REF₃, SrF₂, and Li₂(CN₂) at around 600 °C. The crystal structure of Li₂Gd₂Sr(CN₂)₅ was solved based on X‐ray single‐crystal diffraction data. Corresponding Li₂RE₂Sr(CN₂)₅ compounds were analyzed by isotypic indexing of their powder patterns. The crystal structure of Li₂Gd₂Sr(CN₂)₅ can be well related to that of Gd₂(CN₂)₃, because both structures are based on layered structures composed of close packed layers of [N=C=N]^2– sticks, alternating with layers of metal ions. The crystal structure of Li₂Gd₂Sr(CN₂)₅ can be considered to contain an ABC layer sequence of [N = C=N]^2– layers with the interlayer voids being occupied by (three) distinct types of cations.