Spectrochemical properties of molybdo- and tungsto-heteropolyanions containing Ce(IV) or Ce(III) as a heteroatom

The absorption and MCD spectra in the VIS-UV region of the traditional Silverton-type polyanion [Ce(IV)Mo₁₂O₄₂]^8? and Weakley-type polyanions, [X(W₅O₁₈)₂]^itn? [X = Ce(IV) and Ce(III)], have been measured and two charge-transfer transitions, ligand-to-heteroatom and intra-ligand, are discussed.     

Anderson-type heteropolyanions of molybdenum(VI) and tungsten(VI)

The previously reported preparation of some Anderson-type molybdopolyanions containing divalent metal ions (Zn, Cu, Co or Mn) as a heteroatom has been reinvestigated. The molybdopolyanions of Zn(II) and Cu(II) were confirmed, although the Cu(II) polyanion was not stable and could not be recrystallized. On the other hand, the polyanions of Co(II) and Mn(II) could not be reproduced. Another type of heteropoly compound, [X(H₂O)_6-x(Mo₇O₂₄)]⁴⁻ [X = Cu(II), Co(II) or Mn(II)], was isolated as solids, which are not stable thermally. The mixed-type Anderson polyanions, [Ni(II)Mo_6-xW_x,O₂₄H₆]⁴⁻, which have been questioned as mixtures of species with different x values, were also reinvestigated using IR, UV absorption and MCD spectra. They are single species, but not mixtures, although some positional isomers may be present for the compounds where x = 2-4. The possibility of oxidation of the heteroatom with the Anderson structure maintained was examined. The oxidation of [Ni(II)Mo₆O₂₄H₆]⁴⁻ by the S₂O²⁻₈ ion in aqueous solution gave the Waugh-type [Ni(IV)Mo₉O₃₂]⁶⁻ polyanion, whereas the oxidation of [Ni(II)W₆O₂₄H₆]⁴⁻ gave no heteropoly compound.     

Mandelazo I As A Reagent For Zr(IV) Determination

Abstract

A spectromeric study of the reaction of the Zr(IV) ions with Mandelazo I was carried out. Absorption spectra revealed that the maximum absorption of the zirconium compound appears at a wavelength (316 nm) different from the maxima of the reagent (253 and 390 nm). Beer-Lambert law is followed for zirconium concentrations of the order of 8.8x 10^?5 M (i.e. 8 μg Zr (IV)/mL). Possible interferences of ions such as Be(II), Cu(II), Zn(II), Al(III), Th(IV), U(VI), Mn(II), Fe(III), Co(II) and Ni(II) were investigated in connection with some masking agents such as SO₄ ^2- and C₂O₄ ^2-. Also, the solid state Zr(IV)-Mandelazo I compound was prepared and characterized by nitrogen and thermogravimetric analyses.     

Magnetic circular dichroism of manganese pentacarbonyl bromide

The absorption and magnetic circular dichroism (MCD) spectra of manganese pentacarbonyl bromide Mn(CO)₅Br in a solution of 2-methyl tetrahydrofuran were measured at various temperatures over the 3500–4500 Å region. Within experimental error the MCD spectra are not temperature dependent and in addition to a negative B term exhibit a positive A term, indicative for a degenerate excited state. Following the irreducible tensor method we conclude that the transition involved will be mainly e[π, Br] → a₁[σ^*, 3d₂²] and for the excited state we calculate a magnetic moment which agrees quite closely with the experimental value.     

Polarized crystal spectra of the mixed metal salt [(CH3)3NH]MnxCu1−xCl3·2H2O

The electronic absorption spectra in two polarizations are reported for crystals of the dichroic salt, TMAMn_xCu_1?xCl₃·2H₂O where TMA represents the trimethylammonium cation, (CH₃)₃NH⁺. Although TMACuCl₃·2H₂O is monoclinic, the mixed metal salts in which x ≥ 0.20 adopt the orthorhombic structure of TMAMnCl₃·2H₂O. The bands observed in the near ir region are adequately explained as d-d transitions of the Cu(II) ion in D_2h symmetry. Other polarized bands which occur in the visible region and are neither Mn(II) nor Cu(II) d-d transitions are discussed.     

Near ultraviolet spectroscopic studies of 2,4-diamino-6-piperidinopyrimidine-3-oxide (minoxidil) and 2,4-diamino-6-piperidinopyrimidine (desoxyminoxidil)

The near u.v. spectra of 2,4-diamino-6-piperidinopyrimidine (desoxyminoxidil) and 2,4-diamino-6-piperidinopyrimidine-3-oxide (minoxidil) can be viewed as perturbed pyrimidine spectra. The u.v. properties of pyrimidine and a series of aminopyrimidines, specifically 2,4,6-triaminopyrimidine, are examined to obtain u.v. spectral assignments for desoxyminoxidil and minoxidil. Minoxidil and its desoxy counterpart have C_s symmetry, and all π → π* absorptions are allowed ¹A′ ← ¹A′ transitions. The two lowest energy π →- π* absorptions observed in minoxidil (262 nm, 292 nm) are tentatively assigned as very mild oxygen → pyrimidine ring charge-transfer transitions. Intensity decreases in protic solvents, and the results of simple Hückel molecular orbital calculations indicate that the 292 nm transition has more charge-transfer character than the 262 nm absorption. The protonated species of desoxyminoxidil and minoxidil have very similar u.v. spectra. This is due to the lack of oxygen-related charge transfer in protonated minoxidil, and the high probability that the positive charge resides in similar environments in the minoxidil and desoxyminoxidil molecular frameworks.     

Darstellung und Charakterisierung von Tetrakis(Chloro-Bromo)-Oxalato-Osmaten(IV)

Preparation and Characterization of Tetrakis(chloro-bromo) Oxalatoosmates(IV) On treatment of [OsBr₄ox]^2? with Cl^? the yellow to orange coloured complexes [OsCl_nBr_4?nox]^2?, n = 1, 2, 3, are formed. The separation of geometric isomers is difficult but possible by ion exchange chromatography on diethylaminoethyl cellulose. The 10 K absorption spectra show in the UV/VIS region intensive Br←Os and Cl←Os charge transfer bands and in the NIR weak intraconfigurational transitions splitted by spin-orbit coupling and lowered symmetry into 5 components. A very weak spin-forbidden d—d-transition at about 600 nm is improved as a luminescence absorption band in the Raman spectrum.     

Solvent Effects on the piezochromism of molybdenum(IV) and tungsten(IV) anions [M(CN)3O(diimine)]−

Solvatochromism of the [Mo(CN)₃O(phen)]⁻ ion has been studied. Solvent effects on pressure dependence (up to 1.25 kbar) of wavelengths of maximum absorption for charge-transfer bands of several molybdenum(IV) and tungsten(IV) complexes, [M(CN)₃O(diimine)]⁻ (M = Mo or W), are described. The effects of applied pressure are larger for less polar unstructured solvents than for highly polar hydrogen-bonded solvents. This revised version was published online in June 2006 with corrections to the Cover Date.     

Matrix isolation magnetic circular dichroism (MCD) spectrum of NH radical produced by a glow discharge technique

MCD and absorption spectra are reported for the X(³Σ^?)→A(³H_i transition of NH produced by a glow discharge and isolated in Ar and Xe matrices. The MCD is strongly temperature dependent and is detectable at concentrations well below those required in a conventional absorption measurement.     

Contribution de la spectrometrie X à l'étude du manganèse dans les oxydes mixtes de structure spinelle: Analyse du spectre MnKβ et du seuil d'absorption K

Chemical shifts of Kβ_1,3 and Kβ₅ emission bands and X-ray absorption spectra near the K edge have been measured in several manganese spinel oxides with the metal in the formal oxidation states +2, +3, and +4. The position of line MnKβ_1,3 is determined mainly by the valence of manganese. The relative intensity of Kβ′ satellite with respect to the Kβ_1,3 line gives qualitative information about the presence of Mn(II) in mixed oxides. Mn(IV) oxides are characterized by a small chemical shift of the Kβ₅ band unlike Mn(II) and Mn(III) compounds. The first high resolution XANES spectra for these materials were performed at the DCI storage ring at LURE (Orsay, France). The chemical shifts ΔE (K absorption discontinuty) and ΔE_max (main peak) are correlated with the oxidation state of metal. Spectra of Mn³⁺ and Mn⁴⁺ ions in the octahedral environment are characterized by the splitting of 1s → 3d transitions (2 eV). In mixed oxides, the first Mn(II) 1s → 4s-4p transition is observed as a peak (or shoulder) located at 7 eV above the 1s → 3d transition. The study of the X-ray absorption fine structure in the near edge region can be used for qualitative solid-state analysis of mixed oxides such as NiMn₂O₄ or CuMn₂O₄.     

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.     

Erratum

Peculiar transitions in the optical spectra of Mn atoms isolated in argon matrices confirm the existence of Mn₂ molecule. The temperature variation of the absorption and MCD intensity in the range 13-27 K demonstrate that the Mn₂ molecule is antiferromagnetic and allows a precise determination of its ground-state exchange energy: J = ?10.3 ± 0.6 cm^?1.     

Spectroscopic and electrochemical properties of dichlorodiimine complexes of Au(III) and Pt(II) with 1,4-diazine derivatives of o-phenanthroline

A series of dichlorodiimine complexes [M(N N)Cl₂]^z of Au(III) and Pt(II) with 1,4-derivatives of o-phenanthroline [(N N) = o-phenanthroline (phen), dipyrido[f,h]quinoxaline (dpq), dipyrido[a,c]phenazine (dppz), 6,7-dicyanodipyrido[f,h]quinoxaline (dicnq)] were prepared and characterized by ¹H NMR, electronic absorption, and emission spectroscopy and by cyclic voltammetry. In all the complexes, the ³(π-π*)-type transition is the spin-forbidden transition of the lowest energy, responsible for the luminescence. The longest wave bands in the absorption spectra of the Au(III) and Pd(II) complexes were assigned in accordance with the results of the electrochemical studies to the ¹(d*)-and ¹(d*)-type transitions, respectively.     

UV-VUV-excited photoluminescence of RE-activated CaLaP3O10 (RE=Eu,Tb)

Monazite-type polyphosphate CaLaP₃O₁₀ was synthesized by solid-state reaction at 1000 °C and their photoluminescence of Eu³⁺ and Tb³⁺ in CaLaP₃O₁₀ under ultraviolet (UV) and vacuum-ultraviolet (VUV) excitation were evaluated for the first time. The emission spectra of CaLaP₃O₁₀:Eu³⁺showed that Eu³⁺ are in a site with inversion symmetry because the magnetic dipole transition ⁵D₀-⁷F₁ was the strongest both upon 254 and 147 nm excitation. Monitored at 621 nm the excitation spectra consisted of host absorption bands, charge transfer band of Eu-O and the intraconfiguration 4f⁶ transition of Eu³⁺. Green phosphor CaLaP₃O₁₀:Tb³⁺exhibited better color purity when excited by 147 nm than that excited by 254 nm. With monitored at 542 nm the host absorption bands of CaLaP₃O₁₀:Tb³⁺ were also observed. Besides the host absorption bands there were strong f-d and weak f-f transitions of Tb³⁺.     

Single crystal circular and linear dichroism spectra and absolute configuration of M(en)3(NO3)2 (M = Zn(II), Cu(II), Ni(II), Co(II), Mn(II) and Ru(II)

The isomorphous single crystals of M(ethylenediamine)₃(NO₃)₂, where M is Zn(II), Ni(II) and Co(II), exhibit macroscopic optical activity as predicted by their acentric space group. Axial circular dichroism measurements on these pure crystals show conclusively that spontaneous resolution has occurred. The axial circular dichroism and orthoaxial linear dichroism spectra of these pure crystals, and of Cu(II), Ni(II), Co(II), Mn(II) and Ru(II) doped into the Zn(en)₃(NO₃)₂ crystal have been measured at ambient and cryogenic temperatures in the range from 7 to 35 kK. The first NO₃^? transition at 32.5 kK is assigned as ¹A ← ¹A based on its linear polarization and sign of rotational strength. The d-d transitions are assigned in the context of D₃ symmetry and reveal a small negative crystal field parameter k, consistent with theoretical prediction. A positive R for all d-d transitions is found to be associated with the Λ configuration for all of the complex ions, by correlation with the crystal and solution circular dichroism of Ru(en)₃²⁺.     

1H NMR study of isomerization in chlorotin(IV) ternary complexes of 8-quinolinol and 5,7-dichloro-8-quinolinol

A complete analysis of the temperature dependence (?30 to 52°C) of the ¹H NMR spectra in d-chloroform of the ternary complexes, bis-(8-quinolinato)tin(IV) dichloride and bis-(5,7-dichloro-8-quinolinato)tin(IV) dichloride has been performed. The intramolecular character of the exchange process has been established, and the spectra have been analyzed by the total lineshape method in terms of the interconversion of two isomers, the cis-cis-trans and the cis-trans-cis (with respect to Cl, N and O atoms), including the tin-proton couplings in the simulations. Arrhenius parameters of the process were E_a = 54 ± 1 and 52 + 1 kJ mol^?1, and log A = 11.8 ± 0.2 and 11.7 ± 0.3, respectively, for the two complexes. The similarity of the activation parameters obtained for both complexes indicates that the presence of bulky Cl atoms in the 8-quinolinol ring had no appreciable energetic influence on the isomerization process. Data were compared with those reported for other chlorinated hexacoordinated complexes, involving ligands other than the 8-quinolinol ring.     

Luminescence of ortho-metallated platinum(II) complexes

The absorption spectra, emission spectra, and emission lifetimes of Pt(Phpy)₂, Pt(Thpy)₂, and Pt(Bhq)₂ complexes (Phpy⁻, Thpy⁻, and Bhq⁻ are the ortho C-deprotonated forms of 2-phenylpyridine, 2-(2-thienyl)-pyridine, and benzo(h)quinoline) have been studied and compared with those of the C-protonated neutral ligands. For all complexes examined the low-energy absorption bands in the near UV and visible region are assigned to metal-to-ligand charge-transfer transitions. The strong and structured luminescence emissions observed in the 500–600 nm region (lifetime in the microsecond range at 77 K) are assigned to metal-to-ligand charge-transfer excited states.     

Kalium-Hexacyanomanganat(IV): Präparation und Spektren

Potassium Hexacyano-mianganate(IV): Preparation and Spectra K₂[Mn(CN)₆] and so far not described K₂[Mn(CN)₆] · 3DMF were prepared in analytical purity. IR, Raman and UV spectra of both compounds are given and discussed. The spin-forbidden ²E_g, ²T_1g — ⁴A_2g transition proves the Racah parameter B₅₅ and the nephelauxetic ratio β₅₅ to be 651 em^?l and 0.61 respectively.     

Theoretically derived absorption and MCD spectral data for the cellular species produced in the hydrolysis of cis-diamminedichloroplatinum(II)

The cellular species formed in the hydrolysis of cis-Pt(NH₃)₂Cl₂ (DDP), namely, cis-[Pt(NH₃)₂XY]ⁿ⁺ (X, Y = Cl^?, H₂O, OH^?; n = 0, 1, 2) have been investigated theoretically using the relativistic and nonrelativistic extended Huckel molecular orbital method. Molecular orbital (MO) results for trans-DDP and its hydrolysis products are also reported for comparison. Transition energies, molar absorption coefficients (?), and B terms from magnetic circular dichroism (MCD) derived from theory are presented for each of the species studied. The electronic absorption and MCD spectra of all the complexes are predicted to exhibit ligand field transitions arising primarily from excitations between the occupied Pt 5d orbitals and the unoccupied Pt 5d and 6p_z orbitals, respectively. The 5d → 6p_z transitions are expected to yield intense absorptions in the UV spectral region. Some intensity is generated in the d → d transitions as a result of the low symmetry of these complexes. Correlation of available experimental data with theory allows spectral assignments to be made and predicted. Substituent effects in the cis- and trans-isomeric species are discussed. Finally, the applicability of the EHMO method to these systems is examined.