X-ray photoelectron,emission, and absorption studies of the electronic structure of molybdenum and tungsten trisulfides and their intercalates

The electronic structure of molybdenum and tungsten trisulfides and their lithium intercalates is investigated by X-ray emission, absorption, and photoelectron spectroscopy. The electron density of lithium atoms intercalated into molybdenum and tungsten trisulfides is distributed over both the metal and sulfur atoms, with more over the atoms of the disulfide pair. These compounds are assumed to have an additional donor-acceptor bond involving a lone pair of disulfide sulfur atom electrons and the vacant levels of the metal. A qualitative scheme of the electronic structure of MoS₃ is constructed based on experimental results and assuming the presence of a donor-acceptor bond. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 6, pp. 81–93, November–December, 1994. Translated by L. Smolina     

The electronic structure of methyl lithium

The results of SCF—MO calculations using a large Gaussian basis set are reported for methyl lithium CH₃Li. Particular attention is paid to obtaining chemically useful informa- tion from the wavefunction, and a comparison is made with the results recently reported for NH₃Li⁺, which is isoelectronic with CH₃Li. Significant differences in their electronic structures are evident on examining the electron density and density difference maps together with population analysis indices.     

C28 fullerites-structure, electronic properties and intercalates

Mechanical and electronic properties of hypothetical carbon nanostructures, on the basis of C28 building blocks, hyperdiamond and hyperlonsdaleite, have been investigated with DFT based methods. The low mass density and large internal surface suggest applications as catalyst, nanosieve and gas storage material. We estimate the active volume accessible by H2. Special emphasis is given to the possibility to tune their properties by endo- and exohedral intercalation with Zn, Ti and K. While endohedral intercalation with Zn does not affect the overall structure, endohedral Ti intercalation has different consequences on the structural stability of the two allotropes. Exohedral intercalation with K leads to an ionic fullerite phase with metallic conductivity.     

Quantum-chemical investigation of spatial and electronic structure of verdazyl and its derivatives

The unrestricted HF method in the INDO approximation with optimized geometry was used to describe the electronic structure of the hetero-ring of verdazyl and the derivatives of the latter. The results obtained are in good agreement with the experimental EPR spectra of triphenylverdazyl radical and its dipole moment. These data may be a basis for understanding and predicting the chemical properties and reactivity of verdazyl and its derivatives.     

The electronic structure of small lithium clusters

Ab initio molecular orbital calculations using the STO-6G and STO6-21G basis sets have been performed for the cluster series Li _n ⁺ , Li _n , and Li _n ^– (wheren=2–7). Thirty-two optimized structures are discussed and reported, many of which (especially for the anionic structures) have not yet been considered. The calculations suggest that for all three species the optimum geometries are planar. Of the two levels of theories that were investigated, STO-6G//STO-6G and STO6-21G//STO-6G, the latter hybrid theory was found to be less reliable. In particular, for the anionic structures these calculations should provide a platform from which more sophisticated, i.e., configuration interaction, geometry optimization can be performed.     

双核草酸钼的合成与结构

合成了新化合物(N~2H~6)~0~.~5[(CH~3)~4N]{[MoO(H~2O)C~2O~4]~2(μ^2-O)~2}·H~2O,并运用元素分析、红外和单晶X衍射对其结构进行了表征。测定结果证实该化合物有两个共边连接的钼氧八面体,钼原子都是正五价,且有Mo－Mo键存在,每个钼上有一个螯合配位的草酸根。该化合物属单斜晶系P2~1/c,a=0.6059(1)nm,b=1.6658(3)nm,c=1.8249(4)nm,β=94.02(3)°,V=1.8374(6)nm^3,R~1=0.0337,wR~2=0.0908。     

三核钼原子簇化合物的EPR和电子结构

本文报道一个新的三核钼原子簇化合物在室温和77K固态和液态的EPR谱,这些谱均呈现出a,b两套谱线的叠加,分析谱线的强度比,线宽和谱参数,认为g值较大的a谱归属于三核钼原子簇化合物,而b谱归属于单核钼杂质。从由X射线晶体结构方法确定的空间结构出发,三核钼原子簇化合物可能有两种分子形式:Mo3(μ3-S)(μ2-S)3Cl[S2P(OEt)2]4 1Mo3(μ3-S)(μ2-S)(μ2-Cl)2Cl[S2P(OEt)2]4 2分别用简单量子化学理论和EHMO法计算出未配对电子所处的分子轨道,求出g1和g1,并与EPR实验值相比较,认为该化合物的分子式应为2,簇骼{Mo3}属七电子体系,在77K温度下,其未配对电子主要局域在三个钼原子所组成的近似等腰三角形簇骼的顶点钼原子周围。     

An XES and XPS study of the electronic structure of molybdenum complexes

The AlKα excited X-ray photoelectron spectra of the valence and the core regions and the SKβ, SKα and MoLβ₂ X-ray emission spectra of Li₂MoO₄, (NH₄)₂MoS₄, K₃Mo(SCN)₆ and K₂WS₄ have been measured. The major peaks in the photoelectron spectra of the valence region are identified comparing XPS, XES and theoretical data from semiempirical and ab initio calculations. The highest occupied valence level in tetrathiomolybdates is concluded to be t₁. The atomic charge on sulfur is estimated using the SKα shifts with the aid of a free ion model.     

Electronic structure and electronic absorption spectra of molybdenum and tungsten oxotetrachlorides

Electronic absorption spectra of the molecules MoOCl₄ and WOCl₄ have been measured and their electronic structure has been calculated on the basis of the SCF-X-SW theory in the overlapping atomic sphere model. Ionisation potentials and allowed optical transition energies have been found in the transition state approximation. The interpretation of the electronic absorption spectra of gaseous MoOCl₄ and WOCl₄ is given.     

Synthesis and electronic structure of highly electron-accepting radiaannulene and its reduced species

Highly electron-accepting radiaannulene (1) was synthesized. CV measurements revealed a high electron accepting ability and strong electronic coupling in the anionic species. Spectroelectrochemical analysis revealed a very low-energy absorption band in the spectra of 1⁻ and 1²⁻.     

An electronic structure investigation of the BNO-BON-NBO system

The potential energy hypersurface of the ground triplet states of the BNO-BON-NBO system has been investigated using traditional ab initio electronic structure theory. The molecules studied have the molecular formula BON and include three linear and three angular species, and two transition states for the isomerization of an angular N-B-O to an angular B-O-N and a linear B-NO, respectively. All stationary points on the BNO-BON-NBO isomerization potential energy surface have been characterized employing UMP2, UMP4, and Gaussian-2 (G2) theory with the 6-311G(d), 6-311G(2d), and TZ2P basis sets. The isomerization for an angular N-BO to the linear B-NO has a lower energy barrier than that of the former to an angular B-ON. Energetics are presented with G2 energies. Two sets of resonance structures for both bent B-NO (boron nitrosyl) and B-ON (boron isonitrosyl) were proposed and the bonding in the two species was analyzed. For the purpose of comparison, the density functional theory based hybrid methods B3LYP/6-311G(d) and B3LYP/TZ2P have also been applied to both geometry optimization and single-point calculations. It is found that the B3LYP prediction of the nature of the linear B-O is contradictory to that made by all MPn(n = 2 and 4) calculations. The cause for this contradiction is discussed.     

Synthesis and luminescent properties and theoretical investigation on electronic structure of nitrile-based 2-pyridone molecules

3-Cyano-4,6-dimethyl-2-pyridone and 3-cyano-4-methyl-6-phenyl-2-pyridone were synthesized effectively by the reaction of readily available 1,3-diketone and malononitrile directly and in good yield. Upon photoexcitation, 3-cyano-4-methyl-6-phenyl-2-pyridone in ethanol shows strong blue emission. The ground- and excited-state geometries, charge distributions, and excitation energies of 2-pyridone derivatives were evaluated by ab initio calculations. Organic light-emitting diodes (OLED) made using 3-cyano-4-methyl-6-phenyl-2-pyridone as dopant showed blue light emission with a maximum electroluminescence (EL) emission at around 456 nm.     

Effect of structural defects on the electronic structure and stability of cubic molybdenum carbide

Institute of Chemistry, Ural Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 2, pp. 19–24, March–April, 1989.     

Synthesis and properties of polysiloxane xerogels containing tetrasulfide groups

Polysiloxane xerogels with a functional group content of 1.1?C1.9 mmol/g have been obtained by the hydrolytic condensation of the alkoxysilanes Si(OC₂H₅)₄ and [(C₂H₅O)₃Si(CH₂)₃S₂]₂ in the 2 : 1, 4 : 1, and 8 : 1 ratios. It has been demonstrated by ¹³C and ²⁹Si CPMAS NMR spectroscopy that the xerogels have a polysiloxane framework with dipropyl tetrasulfide bridges, silanol groups, unhydrolyzed ethoxyl groups, and hydrogen-bonded water molecules on the surface. The xerogels have a porous structure. As the molar ratio of the reacting alkoxysilanes is increased in the above-specified range, the specific surface area of the xerogel increases (from 89 to 312 m²/kg) and the same is valid for other structure-adsorption characteristics. The synthesized polysiloxane xerogels readily sorb Hg²⁺ from acidified solutions. Their static sorption capacity can be as high as 1.5 g Hg per gram of sorbent. However, in the course of time, the 1 : 1 complexes forming on the xerogel surface undergo transformations accompanied by the release of mercury sulfide and/or Hg²⁺ reduction to mercury metal.     

Crystal chemistry and electronic structure of the metallic lithium ion conductor, LiNiN

The layered ternary nitride LiNiN shows an interesting combination of fast Li+ ion diffusion and metallic behavior, properties which suggest potential applications as an electrode material in lithium ion batteries. A detailed investigation of the structure and properties of LiNiN using powder neutron diffraction, ab initio calculations, SQUID magnetometry, and solid-state NMR is described. Variable-temperature neutron diffraction demonstrates that LiNiN forms a variant of the parent Li3N structure in which Li+ ion vacancies are ordered within the [LiN] planes and with Ni exclusively occupying interlayer positions (at 280 K: hexagonal space group Pm2, a = 3.74304(5) A, c = 3.52542(6) A, Z = 1). Calculations suggest that LiNiN is a one-dimensional metal, as a result of the mixed pi- and sigma-bonding interactions between Ni and N along the c-axis. Solid-state 7Li NMR spectra are consistent with both fast Li+ motion and metallic behavior.     

Far-infrared investigation of kaolinite and halloysite intercalates using terahertz time-domain spectroscopy

Two clay minerals from the kaolin group, namely well-ordered kaolinite and poorly ordered halloysite, were investigated by terahertz time-domain spectroscopy (THz-TDS). Both clay samples were used for preparation of their respective intercalates using dimethyl sulfoxide (DMSO) and potassium acetate (KAc) with water. The intercalates were also characterized by X-ray powder diffraction and Fourier transform infrared spectroscopy. The dielectric behaviour of clay samples was investigated in the far-infrared region of 0.2–2.7 THz corresponding to about 6.7–89.9 cm⁻¹. The frequency dependence of the power absorption coefficient revealed clear absorption bands for DMSO intercalates but not for KAc with water. For kaolinite – DMSO intercalate a distinct doublet at 1.70 THz (56.6 cm⁻¹) and 1.88 THz (62.6 cm⁻¹), and for halloysite – DMSO intercalate a single broad band centred around 1.72 THz (57.3 cm⁻¹) were found. These bands are reported for the first time in this type of intercalation substances and indicate the application potential of THz time-domain spectroscopy for use in the investigation and detection of chemical behaviour of molecular species introduced into the interlayer space of layered substances such as clays and clay minerals. Additionally, the qualitative characteristics of observed bands of DMSO intercalates in the THz region reasonably resembled the structural order/disorder of used kaolinite and halloysite samples.