Danita de Waal

Raman Spectroscopic Investigations of ZrSiO4:V4+, the Blue Zircon Vanadium Pigment

Powdered and single-crystal samples of the vanadium-containing zircon pigment ZrSiO4:V4+ were investigated by means of Raman spectroscopy, the spectra being recorded between 200 and 1100 cm−1 at ambient conditions. V–O vibrational bands could be identified by comparison with spectra of pure ZrSiO4. The possibility of V4+ occupation of the interstitial 8d site withC2hsymmetry was excluded on group theoretical grounds. V—O bond lengths for ZrSiO4:V4+ were estimated to be between 172 and 175 pm from the Raman band wavenumbers; these bond lengths are much shorter than those (204 and 227.6 pm) expected for V4+ on the Zr4+ site, but similar to that for V4+ on the Si4+ site (175.8 pm). This would indicate substitution on the Si4+ site, 4b, rather than the Zr4+ site, 4a. This conclusion is supported by the influence of V4+ and dopants such as Cr4+, Pr4+ and others on the zircon crystal lattice. The changes in the strengths of Si—O bonds with the change of chromophore incorporated into the structure are reflected in the shifts in wavenumber of the Raman-active zircon modes.

The spin-transition complexes [Fe(Htrz)3](ClO4)2 and [Fe(NH2trz)3](ClO4)2 I. FT-IR spectra of a low pressure and a low temperature phase transition

Abstract Infrared spectra of two spin-transition polymers, [Fe(Htrz) 3 ](ClO 4 ) 2 and [Fe(NH 2 trz) 3 ](ClO 4 ) 2 , were investigated. In the structure, the metal centers are bridged through nitrogen atoms in the 1- and 2-positions of the three triazole ligands, each iron being sixfold coordinated to nitrogen. For comparison, Fourier transform infrared (FT-IR) spectra of a similar, but permanently low-spin compound, [Fe(Htrz) 3 ]Cl 2 , and a permanently high-spin compound, [Fe(Htrz) 3 ]SO 4 , were recorded. Mid-infrared spectra indicate bidentate bridging of triazole ligands. Far-infrared spectra of low-spin [Fe(Htrz) 3 ](ClO 4 ) 2 and [Fe(Htrz) 3 ]Cl 2 indicate six equal FeN bonds for the low-spin coordination sphere. Far-infrared spectra of high-spin [Fe(Htrz) 3 ](ClO 4 ) 2 , [Fe(NH 2 trz) 3 ](ClO 4 ) 2 , and [Fe(Htrz) 3 ]SO 4 indicate weakening of all six FeN bonds in the high-spin state, two of the bonds being weakened to a lesser degree than the other four. A low- to high-spin transition is observed for [Fe(Htrz) 3 ](ClO 4 ) 2 upon lowering the pressure to 110 mbar. The low-temperature high- to low-spin transition of [Fe(NH 2 trz) 3 ](ClO 4 ) 2 was investigated by far-infrared spectroscopy.

Vibrational spectra of NaVO3, KVO3 and the solid solutions (Na0.88K0.12)VO3 and (Na0.5K0.5)VO3

Abstract The phase transition in KVO 3 involving changes in the dielectric properties was investigated by means of Raman spectroscopy. A temperature dependence study of the Raman active modes did not reflect the reported changes in the dielectric properties of the compound around 593 K. Infrared and Raman spectra of the two solid solutions, (Na 0.88 K 0.12 )VO 3 and (Na 0.5 K 0.5 )VO 3 are presented in comparison with those of KVO 3 and α-NaVO 3 . The translational modes of the cations could accordingly be identified unambiguously. The frequency dependence of the various vibrational, rotational and translational modes of the VO − 3 chain on composition is also reported and compared to high pressure behaviour of some NH 4 VO 3 vibrations.

Orbital symmetry in sulphur pigmentary chromophores

Abstract Pictorial molecular orbital theory, in a qualitative approach, is used in order to identify possible structures of the red chromophore in ultramarine red pigments. The known blue S 3 −⋅ molecule is assumed to be the starting reagent in a concerted reaction to form the S 4 molecule. Different proposed structures for the S 4 species are tested. Applying the frontier orbital symmetry rules of Woodward and Hoffmann eliminates the tetrahedral S 4 structure as a possibility.

An infrared and Raman study of the reorientational motions and phase transition in and structure of CsPF6

CsPF6I is face‐centered cubic and the PF6− ions are randomly distributed among the six equivalent orientations in the crystal. The ions librate in equilibrium positions for an average time τ, and also jump from one orientation to another in a time which is much shorter than τ. The six different orientations in CsPF6I are of much lower symmetry than the full molecular one. The full vibrational spectra of CsPF6 are reported over the temperature range of 300–4 K and can be analyzed in Phase I in terms of (Oh,C4v) where C4v denotes the symmetry of the ion and Oh that of the site symmetry S. The polarized Raman spectra of single crystals of CsPF6I are interpreted in terms of all the different orientations of the PF6− ions and excellent agreement is obtained between predicted and experimental results. At 90 K CsPF6 undergoes a phase transition and a crystal structure of P4/nmm‐D4h7 is assigned to Phase II. This transition is of the second order and shows behavior which corresponds to those of critical phenome...

A Raman spectroscopic determination of the decomposition kinetics of ammonium metavanadate, NH4VO3

Raman spectroscopy was used to follow the kinetics of the thermal decomposition of solid ammonium metavanadate, NH4VO3. This method avoids the disadvantages of mass-loss determinations because it monitors directly the amount of reactant present. Time-dependent isothermal measurements of the intensity of the v (VO2)s band at 927 cm−1 have been made between 423 and 443 K. The reaction is deceleratory throughout. Applying the ln-ln method, derived from a generalized Avrami-Erofeev equation, to the experimental data, a value of n = 0.9 was found, i.e. a situation similar to first-order kinetics. An activation energy of EA = 48.6 kJ mole−1 has been calculated for the decomposition process.

Ammonium Hexavanadate, (NH4)2V6O16: Preparation, Crystal Structure, Infrared Spectra and High-Pressure Reactions

Abstract Following a re-examination of several published methods for the preparation of ammonium hexavanadate, single crystals of (NH4)2V6O16 have been grown by a reaction of V2O5 with NH4Cl in hot aqueous solution. They are monoclinic, space group P 21/m , with a = 7.858(2), b = 8.412(2), c = 4.995(1) Å , β = 96.43(2)°, and Z = 1. The structure was refined to R = 0.060, wR = 0.039 for 745 unique reflections. It comprises layers built of V2O8 double square pyramids ( V - O = 1.595- 1.988 Å) and distorted VO6 octahedra ( V - O = 1.589-2.287 Å). The infrared bands of the NH4+- and ND4+- groups in (NH4)2V6O16 and its deuterated analogue can be assigned with a fair amount of certainty at 90 K under the space group P 21/m (C2h2). The N - D stretching modes of isotopically diluted NH3D+-groups in (NH4)2V6O16 are in agreement with the predicted splitting into Cs, Cs and C1(2) components. The frequencies and shapes of these modes seem to suggest that bifurcated hydrogen bonds are formed, closely resembling the corresponding bonds in NH4VO3. The NH4+ ions are dynamic in character in (NH4)2V6O16 and remain so down to temperatures of 90 K. At high temperatures in a closed high-pressure system a redox reaction between vanadium (V ) and ammonia takes place which yields VO2 as main product. Intermediates have been found, but up to now their com position is still unknown.

Porcelain shards from Portuguese wrecks: Raman spectroscopic analysis of marine archaeological ceramics

Raman spectroscopic analysis of shards recovered from two Portuguese shipwrecks, the Santo Espirito (1608) and the Santa Maria Madre de Deus (1643), believed to be carrying porcelains of the Ming period have revealed some interesting and novel results that inform historical ideas of porcelain production. The porcelain body of two of the four shards from the Santa Maria Madre de Deus were found to contain anatase, a low temperature polymorph of titanium dioxide, and β-wollastonite a mineral characteristic of soft-paste porcelains that are made at medium-temperature firing conditions. Previously, β-wollastonite has been found in a range of sixteenth to nineteenth century European porcelains but this is the first report of its detection in porcelain believed to be from the Ming period. These same shards exhibited unusual spectral features that were attributed to the resonance enhancement of rare earth elements that resulted from excitation using a near-infrared source.

Solution phase, solid state and computational structural studies of the 2-aryl-3-bromoquinolin-4(1H)-one derivatives

The structures of the potentially tautomeric 2-aryl-3-bromoquinolin-4(1H)-ones were studied using spectroscopic (NMR, IR and mass), X-ray crystallographic and computational techniques. These systems are found to exist in solution (1H NMR and 13C NMR) and solid state (IR and X-ray) as the NH-4-oxo derivatives, and their carbonyl nature is also corroborated by comparison of their spectroscopic data with those of the corresponding N-methylated and O-methylated derivatives. The presence of the quinolinol (hydroxyquinoline) isomer in the gas phase is confirmed by low and high resolution mass spectrometry.

FT-IR Spectra of Cadmium Calcium Pyrophosphate

The FT-IR spectra of a solid solution of cadmium and calcium pyrophosphate, Cd1.25Ca0.75P2O7, are reported here with reference to the IR spectra of the pure compounds, which are used to obtain further information on the structure of the compound. The modes of the pyrophosphate ion can be obtained without interference from site and factor group splitting due to the C1 site and factor groups.