The polarized optical spectra of the ions Ti3+, V3+, Cr3+, Mn3+, Co3+, and Ni3+ in corundum single crystals have been studied at temperatures from 4.2° to 1200°K. A theory of the band strength based on the point‐charge model and p‐d mixing has been developed and applied to the data with results in fair agreement with experiment. The effects of temperature show that the vibrational‐electronic contribution to band strength is quite small at low temperature but may be appreciable at high temperatures. The crystal‐field parameters have been calculated as convergent lattice sums. The observed trigonal‐field parameter has the opposite sign from that calculated by the point‐charge model if the impurity ion is assumed to occupy an Al3+ ion position in the lattice, but has the same sign as calculated for an ion 0.1 A displaced along the c3 axis toward the empty octahedral site. Details of the spectra have been interpreted as showing that the surroundings of an ion are distorted in some electronic states.

Optical spectra of transition-metal ions in corundum

Toxic and mutagenic effects of chromium(VI). A review

Polyoxometallates as models for oxide catalysts: Part I. An UV-visible reflectance study of polyoxomolybdates: Influence of polyhedra arrangement on the electronic transitions and comparison with supported molybdenum catalysts

The published data of the last decade concerning the mechanism of the Kabachnik–Fields reaction and its significance for the chemistry of organophosphorus compounds as a method for the synthesis of α-amino phosphonates and their numerous functionally substituted derivatives and analogues, such as phosphinates and phosphine oxides, are generalised and systematised. The review discusses the classical version of the Kabachnik–Fields reaction, its modifications with the use of phosphorus chlorides, neutral esters and inorganic phosphorus acids, as well as chemical processes simulating separate steps of the reaction, viz., hydrophosphorylation of imines and amination of α-hydroxy phosphonates. Data on the practical application of α-amino phosphonates are presented. The bibliography includes 253 references.

https://iopscience.iop.org/article/10.1070/RC1998v067n10ABEH000421/pdf

The Kabachnik–Fields reaction: synthetic potential and the problem of the mechanism

Tungsten oxide species form strong acid sites on ZrO 2 supports After calcination at 1000–1100 K and promotion with Pt, these solids catalyze C 7+ alkane isomerization at 400–500 K with much higher selectivity than sulfated oxides or zeolitic acids at similar turnover rates Alkane isomerization proceeds via biomolecular reactions involving hydrogen transfer from alkanes or H 2 , which cause the desorption of isomeric carbocations before β-scission occurs On Pt/SO x -ZrO 2 , carbocation desorption is slow, leading to long surface residence times and extensive cracking On Pt/WO x -ZrO 2 , carbocation desorption is rapid and surface isomerization steps limit n-heptane isomerization turnover rates Saturation coverage by WO x surface species inhibits ZrO 2 sintering and its tetragonal to monoclinic structural transformation High isomerization turnover rates appear to require the presence of WO x clusters on ZrO 2 surfaces X-ray absorption at the W-L 1 and W-L III edges suggests the predominant presence of distorted octahedral species, even after dehydration at 673 K, in all WO x -ZrO 2 samples calcined at 1073 K Tetrahedral species, which lead to a strong pre-edge feature in the W-L 1 absorption edge, are not detectable in these samples UV-visible spectra suggest an increase in WO x domain size with increasing loading These distorted octahedral WO x domains on ZrO 2 differ markedly in structure, reduction rates, and alkane isomerization turnover rates and selectivities from tetrahedral WO x species on Al 2 O 3 

Selective isomerization of alkanes on supported tungsten oxide acids

UV–Vis–NIR spectroscopy and colour of bis(N-phenylsalicylaldiminato)cobalt(II) in a variety of solvents

Spectroscopy of molybdenum(VI) compounds

Vibrational fine structure in the electronic spectra of transition metal compounds. an experimental survey

Copper(II) chromate and dichromate complexes with polypyridines. Physicochemical and reactivity studies

The influence of solvents on the electronic absorption spectra of chromium (III) complexes was investigated. The dependence of the crystal field parameter Dq on dielectric constant as well as Gutmann donor number DN of solvent was found and described. By using the proposed model, unknown in the literature donor numbers for a few alcohols were estimated.

Adam Bartecki

Papers

UV–Vis–NIR spectroscopy and colour of bis(N-phenylsalicylaldiminato)cobalt(II) in a variety of solvents

Spectroscopy of molybdenum(VI) compounds

Vibrational fine structure in the electronic spectra of transition metal compounds. an experimental survey

Copper(II) chromate and dichromate complexes with polypyridines. Physicochemical and reactivity studies

Influence of the Bulk and Donor-Acceptor Properties of Solvent on Ligand Field Spectra