Ionic compound magnetism

In an ionic compound, the partial covalence of a bond formed between a transition metal ion and its ligand modifies the magnetic properties of the cation. It can be seen, for example, that if electrons were... 

The spectroscopic properties of meso-ionic compounds have been discussed in detail elsewhere and the reviewers do not feel that it would be useful to include a comprehensive account here. Ultraviolet, infrared, and nuclear magnetic resonance spectra of meso-ionic heterocycles provide general support for the conjugative interaction that would be expected for aromatic heterocycles, " but detailed interpretation of their spectra is not justifiable. Mass spectrometry has been shown to be particularly useful for distinguishing between pairs of meso-ionic isomers... 

This shift in the Mossbauer line is related to the valence of the studied ion and is very large for Np (40 mm/s). However, most compounds of interest for magnetism are not ionic, and covalency affects the isomer shift. Thus, although one observes some grouping into valence states, it cannot be used alone to assign uniquely a valence state - if any - for Np in non-ionic compounds °. ... 

In solution, all 2,3,4,5-tetraethylstibolide anions 11b are chemically and magnetically equivalent, whereas in the solid state this is only the case for the rubidium and cesium derivatives and the dimeric TMEDA adduct of sodium 2,3,4,5-tetraethylarsolide 11a (M = Na). Exchange and dissociation reactions lead to a magnetic equivalence on the NMR timescale, which can be expected for mainly ionic compounds (Table 5) <20040M3417>. 

An operational description is that one reactant (the more ionic compound with the more electropositive metal) transfers alkyl anions to the other. Thus the four methyl groups in Li2BeMe4 form a distorted tetrahedron around the beryllium, with longer distances to the lithium ions. However, this description is oversimplified. The low-temperature nuclear magnetic resonance (NMR) spectrum of Li3MgMe5 has three different methyl resonances, suggesting structure (14), related to the MeLi tetramer. Ate complexes with zinc and aluminum compounds also form. Electron-deficient bridge-bonded structures, exemplified by the X-ray structure of... 

A reaction which has also been studied spectroscopically in KOH (1 m. to 7 m.) at temperatures between —3° and — 30°C. When ozone is passed into concentrated solution of KOH at these temperatures the solution turns orange-yellow (38). This is due to the appearance of 02 ions which are also responsible for the color of, for example, solid potassium peroxide, which, from magnetic and crystallographic measurements, is an ionic compound of the type K+,02- (39). In dilute aqueous solutions... 

Magnetic perovskite and rocksalt-structured oxides and fluorides. These are highly ionic compounds, in which the calculated coupling constants J indicate the degree of locaHsation of the unpaired electrons on the transition metal sites, and the range of the magnetic (spin-spin) interaction. 

Goodenough, J.B. Wold, A. Wold, R.J. Arnott, R.J. Menyuk, N. (1%1). Relationship Between Crystal Symmetry and Magnetic Properties of Ionic Compounds Containing Mn. Physical Review, Vol. 124, (October 1%1), pp. 373-384, ISSN 0031-899X... 

A detailed review and summary of the experimental data as well as the results of calculations of the efg in the heavy lanthanide metals at low temperatures has been given by Pelzl (1972). It was found that in the metal the radial averages r of the 4f electrons appropriate to the quadrupole interaction are 10% smaller than in ionic compounds. In comparison with the magnetic hyperfine interaction (section 2.1.1.1) the additional reduction arises from increased closed shell shielding (1 Rq) in the metallic case. In addition, the conduction electrons increase the antishielding of the lattice efg due to their greater density outside the atomic sphere via the factor (1 + F) and to an increased Sternheimer factor (1 - 7 ) in the metal. 

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