Cobalt magnetic susceptibility

Electrobalances suitable for thermogravimetry are readily adapted for measurements of magnetic susceptibility [333—336] by the Faraday method, with or without variable temperature [337] and data processing facilities [338]. This approach has been particularly valuable in determinations of the changes in oxidation states which occur during the decompositions of iron, cobalt and chromium oxides and hydroxides [339] and during the formation of ferrites [340]. The method requires higher concentrations of ions than those needed in Mossbauer spectroscopy, but the apparatus, techniques and interpretation of observations are often simpler. 

The electronic spectra and magnetic susceptibility of [Ni(21)Cl2] were found to be consistent with a five-coordinate high spin complex. This complex has greater antitumor activity against P388 lymphocytic leukemia test system in mice than cobalt(II), copper(II), zinc(II) and platinum(II) complexes of 21 [187],... 

Perchlorate ion complexes, 28 255-299 with cobalt group metals, 28 265-268 coordination types, 28 256-260 with copper group metals, 28 273-283 with early transition metals, 28 260-263 electronic spectra. 28 258-259 ESR spectra, 28 260 infrared and Raman spectra, 28 257-258 with iron group metals, 28 263-265 with lanthanides, 28 260-265, 287-288 magnetic susceptibility, 28 260 molar conductivities, 28 260 with nickel group metals. 28 268-273 X-ray crystal structure analysis, 28 256-257... 

JFiq. X-l.—Curves showing the reciprocal of molar magnetic susceptibility of compounds of cobalt(II) as a function of the absolute temperature. 

Complexes related to CoHg(SCN)4, the well-known calibrant used in magnetic susceptibility measurements, have recently been prepared containing silver(I).146,147a In the presence of a number of Lewis bases octahedral adducts such as Co[Ag(SCN)2] -2DMF were obtained. Magnetic moments indicated the presence of high-spin cobalt(II). With nickel(II), two types of complex... 

Along this line, the limitations of the technique used must be recognized. Some measure predominantly bulk properties, e.g., X-ray diffraction and magnetic susceptibility whereas, others are sensitive to surface composition, e.g., adsorption and ESCA. For example, in one reported study only cobalt in tetrahedral coordination was found on a catalyst by diffuse reflection spectroscopy, but magnetic measurements revealed that octahedral cobalt must also be present (10). Thus, it is dangerous to rely on any one method to characterize these catalysts. 

Measurements of the magnetic susceptibility (58) of the cobalt enzyme (Table 5) show that the metal ion is bound as high-spin Co (II). The intensity of the visible absorption makes an octahedral coordination, as well as tetragonal distortions thereof, very unlikely. In the combination with CN, the Co(II) enzyme exhibits the spectral features of tetrahedral model complexes with regard to intensity as well as structure both in the visible and the near-infrared wavelength regions (Fig. 8). The width of the near-infrared band (cf. 20) indicates that the deviation... 

In the case of cobalt substituted Zn-fingers [102], the differences between the chemical shifts for corresponding resonances in the Co(II) and Zn(II) complexes allow the determination of the orientation and anisotropy of the magnetic susceptibility tensor [103]. Similar studies are available for pseudotetrahedral Co(II) in the zinc site of superoxide dismutase [104] and five coordinated carbonic anhydrase derivatives [105]. 

With the PMK ligand a CoCu derivative has been obtained [7] (Fig. 6.7). From the temperature dependence of the shifts (and magnetic susceptibility measurements in solution), the value of J appears to be positive and much smaller than kT [13]. As expected, the hyperfine shifts are the sum of those of the CuZn and ZnCo systems for each proton (Table 6.2). The NMR lines of the copper domain are now quite sharp, even sharper than those of the cobalt domain (Fig. 6.7). Qualitatively, the data can be accounted for if xs of copper is sizably reduced and approaches that of cobalt (and thus the Redfield limit is reached). 

Molybdenum oxide - alumina systems have been studied in detail (4-8). Several authors have pointed out that a molybdate surface layer is formed, due to an interaction between molybdenum oxide and the alumina support (9-11). Richardson (12) studied the structural form of cobalt in several oxidic cobalt-molybdenum-alumina catalysts. The presence of an active cobalt-molybdate complex was concluded from magnetic susceptibility measurements. Moreover cobalt aluminate and cobalt oxide were found. Only the active cobalt molybdate complex would contribute to the activity and be characterized by octahedrally coordinated cobalt. Lipsch and Schuit (10) studied a commercial oxidic hydrodesulfurization catalyst, containing 12 wt% M0O3 and 4 wt% CoO. They concluded that a cobalt aluminate phase was present and could not find indications for an active cobalt molybdate complex. Recent magnetic susceptibility studies of the same type of catalyst (13) confirmed the conclusion of Lipsch and Schuit. 

The optimal activity for a cobalt-molybdenum-alumina catalyst is obtained by calcination at the higher temperatures. This means that the cobalt ions, present as a cobalt aluminate phase according to the reflectance spectra and the magnetic susceptibility measurements, still have a pronounced promoting action after this calcination. The assumption of cobalt present in the surface layer of the alumina lattice explains both the high activity due to the cobalt promotion as well as the presence of the second Lewis band. This configuration is shown schematically in Figure lib. 

The complexation reactions of pilocarpine with cobalt(II), nickel(II), copper(II), and zinc(II) ions were investigated (84). The complexes were characterized by spectrophotometry, conductivity, ESR, NMR, and magnetic susceptibility measurements. In each case, the metal ion was pseudo-tetrahedrally coordinated. Pilocarpine interacts with the metal ion through the imidazole ring. 

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