Chromium complexes physical studies

Chromium(III) complexes, 701 acetates, 869 acetylacetonates, 861 phase chemistry, 863 physical studies, 862 alcoholates, 860 alkoxides, 860 alkyl, 779... 

Trithiolene complexes are also known, for instance those of chromium, molybdenum, and tungsten [592f], having an octahedral geometry. Structures of the complexes above, as well as of a series of other thiolene (thiol) compounds, have been studied using various physical-chemical techniques (x-ray diffraction, NMR, EPR, and UV spectroscopy). Considerable attention has been devoted to their reducing and photochemical properties [1, vol.2]. 

A great deal could be learned by further synthetic studies of unusual complexes of platinum and cobalt, as well as other metals, but the syntheses are long and multistep and few chemists have the patience to attempt them. Knowledge gained by work on the complexes of one metal can be used only indirectly in studies of another the chemistries of the complexes of cobalt(III) and chromium(III), for example, are quite different, although these substances closely resemble each other in physical properties. 

There is some controversy concerning the existence of the a isomers of these tris complexes, Israily reported a purple complex to be or-[Cr(gly)3] however, subsequent workers have shown that this substance most probably was the dihydroxy dimer [Cr2(gly)4(OH)2]. Careful chromatography, on potato starch, of solutions from chromium(III)/glycine reactions yielded red and purple fractions,the electronic spectra of which were consistent with jS and a isomers respectively. Solutions of the a complex were unstable even in the dark and cold. Hoggard has recently claimed the preparation of the a isomer of the glycine complex by a fractional crystallization. The complex was anhydrous, unlike its cobalt(III) analogue. X-Ray powder methods could hence not be used to confirm the identity of the complex the luminescence spectra were held to be consistent with meridional coordination. There have been a number of studies of the physical properties of /S-[Cr(gly)3], summarized in Table 99. 

There is no doubt that Jannik Bjerrum obtained much inspiration from the kinetic and equilibrium studies of his father Niels Bjerrum (1879-1958), the physical chemist (6) best known for his work on chromium(III) complexes. Jannik obtained a comparable success, studying octahedral cobalt(III) conplexes of the N and NgO type (later extended to N O but not beyond S.M.Jj rgensen s type N-O prepared via [(0 NO)2Co(NH2)2] crystals). Jannik s great innovation of using activated charcoal as a catalyst for cobalt (III) equilibria also showed its intrinsic limitations by inducing... 

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