First‐principles calculation of electronic structure of V‐doped anatase TiO2

The energetic and electronic structures of V‐doped anatase TiO₂ have been investigated systematically by the GGA+U approach, including replacement of Ti by V in the absence and presence of oxygen vacancies and the presence of an interstitial site. It was found that V should exist as a V⁴⁺ ion in the replacement of Ti in the anatase lattice, the electron transitions of which to the conduction band from V 3d states are responsible for the experimentally observed visible light absorption. The influence of V dopant concentration on the electronic and magnetic properties is also discussed, such as the influence of the U value in systems containing oxygen vacancies and spin flip phenomena for interstitial V‐doping.     

Electrical Resistivity, Magnetic Susceptibility, X-Ray Photoelectron Spectroscopy, and Electronic Band Structure Studies of Cu2.33−xV4O11

The electronic and physical properties of Cu_2.33V₄O₁₁ were characterized by electrical resistivity, magnetic susceptibility and X-ray photoelectron spectroscopy (XPS) measurements and by tight-binding electronic band structure calculations. Attempts to prepare Cu_2.33−xV₄O₁₁ outside its narrow homogeneity range led to a mixture of Cu_2.33V₄O₁₁, CuVO₃ and β-Cu_xV₂O₅. The magnetic susceptibility data show no evidence for a magnetic/structural transition around 300 K. The XPS spectra of Cu_2.33V₄O₁₁ reveal the presence of mixed valence in both Cu and V. The [Cu⁺]/[Cu²⁺] ratio is estimated to be 1.11 from the Cu 2p_3/2 peak areas, so [V⁴⁺]/[V⁵⁺]=0.56 by the charge balance. Our electronic structure calculations suggest that the oxidation state of the Cu ions is +2 in the channels of CuO₄ tetrahedra, and +1 in the channels of linear CuO₂ and trigonal planar CuO₃ units. This predicts that [Cu⁺]/[Cu²⁺]=1.33 and [V⁴⁺]/[V⁵⁺]=0.50, in good agreement with those deduced from the XPS study.     

Gamma irradiation induced photochemical reactions in V-doped borate glasses

Glasses of the composition XNa₂O · 4Al₂O₃ (96-X) B₂O₃ (mole%) where X = 10, 20, 30 to which 0.03 g V₂O₅ per 100 g glass was added, were prepared by normal melting. Their absorption characteristics together with the corresponding V-free base glasses were determined before and after gamma irradiation. The characteristic spectra of the unirradiated glasses show absorption bands at 315, 470, 560–580, 610–650, 700–870, and 860–1000 nm, indicating the presence of vanadium ions in more than one oxidation state, viz, V⁵⁺, V⁴⁺, and V³⁺. Gamma irradation of V-containing glasses causes the formation of color centers in the glass matrices, with absorption bands at 330, 500, and 610 nm, and photoreduced [V³⁺] and [V²⁺] ions with absorption bands at 350–355 and 530–570 and 520 nm, respectively. Photoreduced [V⁴⁺] may also be formed, giving rise to absorptions at 690–700 and 750–800 nm. The induced vanadium ions are found to absorb at shorter wavelengths than the intrinsic ones. An explanation based on the difference in the field energy of the two states is given.     

Solvent effects on the electronic spectrum of the hexathiocyanatochromate (III) anions. A revised octahedral crystal field splitting parameter for the thiocyanate ion

An early report on the solvent dependence of the electronic spectra of complex ions considered the electrostatic effect of solvent molecules in the second coordination sphere, on the position of the absorption bands.¹ Solvent effects on the ligand field bands for solutions of K[Cr(NH₃₂(NCS)₄] have been discussed by Adamson² who emphasised a correlation between the solvent shifts in the spin-allowed bands and the shifts in the quartet-doublet bands. This work describes the effects of various solvents on the electronic absorption spectra of [Cr(CNS)₆]^3?.     

Frontier orbitals and ligand-to-metal charge transfer electronic transitions in <Emphasis Type="Italic">d</Emphasis><Superscript>0</Superscript>-metal complexes

Properties of frontier orbitals and low-energy electronic transitions in a d ⁰-organometallic complex have been studied by TDDFT and DFT methods using B3LYP hybrid functional and 3-21G*, 6-31G**, SDD, CEP-121G, and DGDZVP basis sets. It has been shown that the electronic transition between frontier orbitals in the excitation and absorption spectra is associated with charge transfer mainly from π-type ligands to a central metal d ⁰-ion. The good agreement of the data (the shape and band position of the spectra of electronic absorption and excitation, energy of electronic transitions, and strength of the harmonic oscillator) of quantum-chemical and photophysical studies is demonstrated.     

Magnetic study of Cr ion in M2CrV3O11−x (MZn, Mg) compounds

Electron paramagnetic resonance (EPR) and magnetic susceptibility measurements on the recently synthesized vanadates M₂CrV₃O_11−x (M=Zn, Mg) have been analyzed. Two absorption lines with g≈2.0 (type I) and g≈1.98 (type II) were recorded in the EPR spectra, which can be attributed to V⁴⁺ ions and Cr³⁺ ion clusters (pairs), respectively. The exchange constant J between Cr³⁺ ions has been calculated, using both EPR and magnetic susceptibility data. Fitting of the EPR and magnetic susceptibility data has been carried out. The sign of J is a negative one for all samples and indicates antiferromagnetic interactions. Some difference in the J constant value among samples has been obtained. Volumetric titration confirms distinctly the presence of vanadium V⁴⁺ ions in the investigated compounds.     

S K and P K absorption spectra and electronic structures of layered thiophosphates MPS3

The S K and P K absorption spectra of layered thiophosphates MPS₃ (M = Mg, Mn, Fe, Ni, Zn, Cd, Sn) were measured. The general features of the S K absorption spectra resemble one another, but the intensity ratio of the first peak to a higher energy structure and the energy position of a shoulder vary, depending on the metal species. All the P K absorption spectra exhibit a prominent peak in the neighborhood of the threshold. It is found that (1) the spectra mainly reveal the p-like partial density of states of the unoccupied energy levels of a [P₂S₆]^4- cluster and (2) the first peak arises predominantly from the electronic transitions to the antibonding levels of the PS bonds. The electronic structures and the optical spectra are discussed.     

Mechanisms of molybdenum substitution in vanadium antimonate

The formation of a solid solution containing the three elements V, Sb and Mo, which are key-elements in the design of light alkane oxidation catalysts, has been studied by incorporating molybdenum into the pure VSbO₄ compound as obtained in air at 700°C (V³⁺_0.28V⁴⁺_0.64□_0.16Sb⁵⁺_0.92O₄). Monophasic compounds with a rutile-type structure have been obtained and characterized by X-ray diffraction, electron microscopy, Infrared Fourier transform, X-ray absorption and electron spin resonance spectroscopies. At low molybdenum content, Mo⁶⁺ substitute V⁴⁺ in the cationic-deficient structure. The charge balance is maintained by an increase of the cationic vacancy number. This leads to the formation of a solid solution corresponding to the formula V³⁺_0.28V⁴⁺_0.64−3xMo⁶⁺_2x□_0.16+xSb⁵⁺_0.92O₄ with 0<x<0.09. At higher molybdenum content, Mo⁵⁺ are stabilized and substitute Sb⁵⁺ in the rutile structure: V³⁺_0.28V⁴⁺_0.37Mo⁶⁺_0.18□_0.25Mo⁵⁺_ySb⁵⁺_0.9−yO₄ with 0<y<0.06. At higher molybdenum content the rutile phase is no longer stable and two new phases are formed: Sb₂O₄ and a new mixed vanadium molybdenum antimonate.     

Magnetic and spectroscopic investigation of partially reduced vanadium pentoxides. II. β′-CuxV2O5

The magnetic, electron paramagentic resonance (EPR), infrared (ir), and optical properties of β′-Cu_xV₂O₅ have been measured and interpreted. Magentic susceptibility studies indicate that β′-Cu_xV₂O₅ undergoes a semiconductor → metal transition near x = 0.60. For x ? 0.40, the magnetic data interpreted in terms of a ligand-field model in which the octahedral ²T_2g term of V⁴⁺ is split by the combined perturbations of axial distortion and spin-oribt coupling, with the result that the ²T_2g term is split into a magnetic ground level, a weakly magentic intermediate level, and a magnetic highest level. The results of the magnetic analysis further support the transition to metallic behavior with increasing x. The EPR spectra are motionally narrowed by electronic hopping at low temperatures, and the g-tensor and linewidth data are in good agreement with the magnetic results. The ir spectra are independent of x and exhibit narrow bands at 1020 and 995 cm^?1, which are attributed to the stretching vibration of multiple VO bonds. The optical spectra consist of two main bands whose peak positions shift to higher frequencies with increasing x, implying that the V⁴⁺O bond distances decrease with increasing x. The results of this study are in excellent agreement with Goodenough's interpretation of β-M_xV₂O₅.     

Extension of High‐Resolution Optical Absorption Spectroscopy to Divalent Neodymium: Absorption Spectra of Nd2+ Ions in a SrCl2 Host

There is a lack of information on electronic spectra of divalent neodymium, and thus the synthesis and characterization of Nd²⁺ systems is now reported. Stabilization of neodymium is observed in a chloride host, which importantly has been accomplished with Nd ions introduced in a divalent state during synthesis, unlike by γ‐irradiation of Nd³⁺ system employed previously. This method yields good‐quality SrCl₂:Nd²⁺ single crystals. For the first time the electronic absorption spectra of Nd²⁺ doped in SrCl₂ have been recorded with high resolution at liquid helium temperature (4.2 K). Identification of the absorption bands occurring in the spectral range of 5000–40 000 cm⁻¹ (2000–250 nm) has been achieved and their tentative assignment proposed. This uniquely detailed Nd²⁺ absorption spectrum provides basis for fingerprinting method enabling identification of the presence of Nd²⁺ ions in future spectra as well as in existing but as‐yet not fully resolved spectra.     

Electronic State of Vanadium Ions in Li1+xV3O8 According to EPR Spectroscopy

EPR spectroscopy is used to study the electronic state of vanadium ions in HT- and LT-Li_1+xV₃O₈. It is shown that in both cases the EPR spectra observed are attributed to vanadyl VO²⁺ ions (localized electron centers) with weak exchange interaction. The other type of registered electrons is characterized by larger mobility through a few V⁵⁺ ions, i.e., by a higher degree of delocalization (electron gas). Based on the analysis of the temperature dependence of the EPR line width, it is stated that the exchange interaction between localized electron centers proceeds through electron gas (C-S-C relaxation). It is found that HT-Li_1+xV₃O₈ differs from LT-Li_1+xV₃O₈ by the sloping form of its spectrum at g_∥ range connected with two types of VO²⁺ ions different in the direction of the crystal field axis corresponding to a short V=O²⁺ bond.     

Synthesis and characterization of mono- and binuclear copper(II) complexes with 2,2′:6′,2″-terpyridine (terpy) and carboxylates: X-ray crystal structure of [Cu(terpy)(OOCH)(OH2)](ClO4) complex

Perchlorate and hexafluorophosphate salts of monomeric [Cu(terpy)(OOCH)(OH₂)]⁺ and dimeric [Cu(terpy)(OOCR)]₂²⁺ cations (terpy = 2,2′:6′,2″-terpyridine, R = CH₃ or C₂H₅) have been synthesized and characterized by IR, electronic and ESR spectra, and analytical data. Spectroscopic results indicate a five-coordinate, close-to-square pyramidal geometry around the copper(II) ion. The half-field absorption in the ΔM_s = 2 region of powdered X-band ESR spectra has been observed for the dimeric species. The crystal structure of [Cu(terpy)(OOCH)(OH₂)](ClO₄) has been determined by X-ray diffraction methods. The compound crystallizes in the space group P2₁/c with unit-cell dimensions: a = 7.341(3), b = 13.919(2), c = 18.081(3) Å, β = 101.68(3)°, V = 1809(1) ų, Z = 4. The structure was refined to R = 0.044, R_w = 0.051.     

Novel clicked tetrathiafulvalene-calix[4]arene assemblies:Synthesis and intermolecular electron transfer toward p-chloranil

Two tetrathiafulvalene-calix[4]arene assemblies（TTF-calix-1 and TTF-calix-2） have been synthesized by the click reaction.Both their cyclic voltammograms show,as expected,two one-electron quasi-reversible redox behavior.The UV-vis absorption spectra studies show that these two assemblies undergo progressive oxidation at the TTF moiety in presence of increasing amounts of Cu²⁺ or Hg²⁺. Moreover,the absorption studies show intermolecular electron transfer between compounds TTF-calix- 1 or TTF-calix-2 and p-chloranil may be promoted by specific metal ions such as Pb²⁺,Sc³⁺ etc.     

Investigation of some oxygen-containing chromium (III) complexes by epr and optical spectroscopy

EPR and electronic absorption spectra of chrome alum solutions in sulphuric and phosphoric acids have been studied. Broadening of the EPR lines and shifts in the positions of the electronic spectra absorption bands were observed at low acid concentrations. In concentrated acids the ⁴T_2g band splits into several well resolved components and the EPR spectra show two resolved areas of fine structure. Each structure may be described by a spinHamiltonian of the form

where D is the zero-field splitting parameter due to the action of the axial crystal fields. The changes in the spectra as the acid concentration is increased are explained by changes in the internal environment of the Cr^III complexes as a result of the substitution of H₂O by anions of the acid residue. The symmetry of the complexes predominating at particular acid concentrations and the parameters D, g and Dt have been determined from an analysis of the EPR and optical absorption spectra. The character of the bond of the Cr^III ion with the surrounding ligands has also been estimated.     

Electronic absorption spectra of solutions of molecular chlorine in molten alkali metal chlorides

Electronic reflection absorption spectroscopy has been used for measuring the electronic spectra of chlorine solutions in molten alkali metal chlorides 2CsCl-NaCl, KCl-NaCl, and CsCl in the range 240–400 nm. Absorption bands of chloride melts are interpreted as electronic transitions in the molecular group Cl₂ and in the triatomic linear group Cl ₃ ^? of symmetry D _∞h and C _∞V .     

EPR and electronic absorption studies of Mn2+ ion in 3CdSO4 · 8H2O single crystals

EPR and electronic absorption spectra of the Mn²⁺ion in 3CdSO₄ · 8H₂O crystals have been studied at 300 K and 80 K. The EPR spectra have     

The charge-transfer absorption band of Eu3+ in oxides

The position of the charge-transfer band of Eu³⁺ in the absorption spectra of a number of oxides is discussed. It is shown that this position is more or less fixed in octahedral VI coordination and that it varies in VIII and XII coordinations as a function of the effective ionic radius of the relevant host lattice ion.     

Absorption spectrum of Yb3+(4f13) IN[(C6H5)3PH]3 YbCl6

Optical absorption spectra taken at 300 and 77 K are reported for six-fold octahedrally coordinated Yb³⁺(4f¹³) in [(C₆H₅)₃PH]₃ YbCl₆. In addition to vibronic spectra we observe electronic transitions which suggest that inversion symmetry is lifted by a small distortion similar to that reported for the Nd³⁺(4f³) spectrum of the corresponding salt. The vibronic as well as the electronic transition have been analyzed on the basis of six-fold octahedral symmetry. The analysis appears reasonable and consistent in comparison with other rare-earth ions that have been studied in similar cubic and octahedral environments.     

First-principles study of cadmium vacancy in CdWO4 crystal

The structural relaxation, electronic structures and optical properties of CdWO₄ crystal containing cadmium vacancy (CWO:V_Cd) are studied by the CASTEP code. The cadmium vacancy (V_Cd) would trap two holes to maintain the local electrical neutrality. The calculated structural relaxation and electronic density of states reveals that the existent form of the hole in CWO:V_Cd should be oxygen molecular ion (O₂^3?). Therefore an associated color center [O₂^3?–V_Cd–O₂^3?] named as V_F center would form in the crystal. The calculated optical absorption spectrum for CWO:V_Cd indicates that this V_F center would cause an absorption band peaking at about 650 nm with a shoulder at around 400 nm, which is in agreement with the experimental optical absorptions of the blue–grey colored CWO crystal.     

Ultraviolet and infrared spectra of substituted indoles

An investigation of the electronic absorption spectra of 5-bromo- and N-methyl indoles in the vapour and liquid state in near u.v. region along with their i.r. spectra in the region 400–4000 cm⁻¹ is presented. The vapour absorption spectra of N-methylindole contains two discrete systems in the region 2906.9-2707.5 Å and 2522-2454 Å. Only one system (2976.2-2844.8 Å) has been photographed in case of 5-bromoindole. The observed bands are interpreted in terms of fundamentals, combinations and overtones. The solution phase spectra contain very limited number of bands in each case. The position of these bands together with the nature of solvents used, has been an indicative of the fact that there is sufficient delocalization of the electrons over both the rings.