Assignment of the vibrational spectra of lithium hydroxide monohydrate, LiOH·H2O

Study of the Structure and Infrared Spectra of LiF, LiCl and LiBr Using Density Functional Theory (DFT)

The paper presents a study of the crystal structure of anhydrous halides LiF, LiCl and LiBr using density functional theory. Models composed of 125 atoms were used for this study. The theoretical values of the lattice parameters and the distribution of charges in the crystals were determined. Using the assumed models at the level of theory DFT/B3LYP/6-31+g*, the theoretical infrared spectra of lithium halides (LiF, LiCl and LiBr) were calculated for the first time. Additionally, measurements of experimental far-infrared (FIR) spectra were performed for these salts. All the obtained theoretical values were compared with experimental data obtained by us and those available in the literature.

Hydration of LiOH and LiCl-Near-Infrared Spectroscopic Analysis

The hydration behavior of LiOH, LiOH·H2O, and LiCl was observed by near-infrared (NIR) spectroscopy. Anhydrous LiOH showed two absorption bands at 7340 and 7171 cm-1. These NIR bands were assigned to the first overtone of surface hydroxyls and interlayer hydroxyls of LiOH, respectively. LiOH·H2O showed two absorption bands at 7137 and 6970 cm-1. These NIR bands were assigned to the first overtone of interlayer hydroxyls and H2O molecules coordinated with Li+, respectively. The interlayer OH- and the coordinated H2O of LiOH·H2O were not modified even when the LiOH·H2O was exposed to air. In contrast, anhydrous LiOH was slowly hydrated for several hours, to form LiOH·H2O under ambient conditions (RH 60%). Kinetic analysis showed that the hydration of the interlayer OH- of LiOH proceeded as a second-order reaction, indicating the formation of intermediate species-[Li(H2O) x (OH)4]3- (x = 1 or 2). However, the hydration of the LiOH surface did not follow a second-order reaction because the chemisorption of H2O molecules onto the defect sites of the LiOH surface does not need to crossover the energy barrier. Furthermore, we succeeded in observing the hydration of deliquescent LiCl, including the formation of LiCl solution for several minutes by NIR spectroscopy.

Siloxyaluminate and Siloxygallate Complexes as Models for Framework and Partially Hydrolyzed Framework Sites in Zeolites and Zeotypes

Anionic molecular models for nonhydrolyzed and partially hydrolyzed aluminum and gallium framework sites on silica, M[OSi(OtBu)₃ ]₄ ^- and HOM[OSi(OtBu)₃ ]₃ ^- (where M=Al or Ga), were synthesized from anionic chlorides Li{M[OSi(OtBu)₃ ]₃ Cl} in salt metathesis reactions. Sequestration of lithium cations with [12]crown-4 afforded charge-separated ion pairs composed of monomeric anions M[OSi(OtBu)₃ ]₄ ^- with outer-sphere [([12]crown-4)₂ Li]⁺ cations, and hydroxides {HOM[OSi(OtBu)₃ ]₃ } with pendant [([12]crown-4)Li]⁺ cations. These molecular models were characterized by single-crystal X-ray diffraction, vibrational spectroscopy, mass spectrometry and NMR spectroscopy. Upon treatment of monomeric [([12]crown-4)Li]{HOM[OSi(OtBu)₃ ]₃ } complexes with benzyl alcohol, benzyloxide complexes were formed, modeling a possible pathway for the formation of active sites for Meerwin-Ponndorf-Verley (MPV) transfer hydrogenations with Al/Ga-doped silica catalysts.

Mechanical and electromechanical properties of functionalized hexagonal boron nitride nanosheet: A density functional theory study

Hydroxylation as a technique is mainly used to alter the chemical characteristics of hexagonal boron nitride (h-BN), affecting physical features as well as mechanical and electromechanical properties in the process, the extent of which remains unknown. In this study, effects of functionalization on the physical, mechanical, and electromechanical properties of h-BN, including the interlayer distance, Young's modulus, intrinsic strength, and bandgaps were investigated based on density functional theory. It was found that functionalized layers of h-BN have an average distance of about 5.48 Å. Analyzing mechanical properties of h-BN revealed great dependence on the degree of functionalization. For the amorphous hydroxylated hexagonal boron nitride nanosheets (OH-BNNS), the Young's modulus moves from 436 to 284 GPa as the coverage of -OH increases. The corresponding variations in the Young's modulus of the ordered OH-BNNS with analogous coverage are bigger at 460-290 GPa. The observed intrinsic strength suggested that mechanical properties are promising even after functionalization. Moreover, the resulted bandgap reduction drastically enhanced the electrical conductivity of this structure under imposed strains. The results from this work pave the way for future endeavors in h-BN nanocomposites research.

Vibrational spectroscopy of metal methanesulfonates: M = Na, Cs, Cu, Ag, Cd

In this work, we have used a combination of vibrational spectroscopy (infrared, Raman and inelastic neutron scattering) and periodic density functional theory to investigate six metal methanesulfonate compounds that exhibit four different modes of complexation of the methanesulfonate ion: ionic, monodentate, bidentate and pentadentate. We found that the transition energies of the modes associated with the methyl group (C-H stretches and deformations, methyl rock and torsion) are essentially independent of the mode of coordination. The SO₃ modes in the Raman spectra also show little variation. In the infrared spectra, there is a clear distinction between ionic (i.e. not coordinated) and coordinated forms of the methanesulfonate ion. This is manifested as a splitting of the asymmetric S-O stretch modes of the SO₃ moiety. Unfortunately, no further differentiation between the various modes of coordination: unidentate, bidentate etc … is possible with the compounds examined. While it is likely that such a distinction could be made, this will require a much larger dataset of compounds for which both structural and spectroscopic data are available than that available here.

A universal surface enhanced Raman spectroscopy (SERS)-active graphene cathode for lithium–air batteries

A uniform SERS-active graphene electrode was used in lithium–oxygen batteries.

Density functional theory in the solid state

Density functional theory (DFT) has been used in many fields of the physical sciences, but none so successfully as in the solid state. From its origins in condensed matter physics, it has expanded into materials science, high-pressure physics and mineralogy, solid-state chemistry and more, powering entire computational subdisciplines. Modern DFT simulation codes can calculate a vast range of structural, chemical, optical, spectroscopic, elastic, vibrational and thermodynamic phenomena. The ability to predict structure-property relationships has revolutionized experimental fields, such as vibrational and solid-state NMR spectroscopy, where it is the primary method to analyse and interpret experimental spectra. In semiconductor physics, great progress has been made in the electronic structure of bulk and defect states despite the severe challenges presented by the description of excited states. Studies are no longer restricted to known crystallographic structures. DFT is increasingly used as an exploratory tool for materials discovery and computational experiments, culminating in ex nihilo crystal structure prediction, which addresses the long-standing difficult problem of how to predict crystal structure polymorphs from nothing but a specified chemical composition. We present an overview of the capabilities of solid-state DFT simulations in all of these topics, illustrated with recent examples using the CASTEP computer program.