Intermediate oxides magnetic properties

The magnetic properties of Pu compounds in different oxidation states are reviewed. New measurements on Pu(C8H8)2, PuFi, [(C2Hs)itN]2PuCl6, and [ (C2H5)itN]itPu(NCS)s are presented. The interpretation of the data is based on intermediate, j-j mixed crystal field states and orbital reduction due to covalency. Especially in the case of the organometallic compounds a large orbital reduction is found. 

The most appropriate description of the Ni oxidation state in all forms of the enzyme appears to be Ni(II), based on a valence bond sum analysis of the best EXAFS model (Thorp, H. H., University of North Carolina, unpublished data). This model is in agreement with studies of the magnetic properties of the EPR silent intermediate of the H2ase from D. baculatus that demonstrated that the Ni site was diamagnetic, albeit in an enzyme that has a selenocysteinate Ni ligand (29). 

Structural information about simple Ni(iii) compounds is limited to those containing F or 0. KsNiFg has been assigned the KsFeFg structure and has a moment of 2-5 BM, intermediate between the values for low- and high-spin. It contains octahedrally coordinated Ni(iii). Oxides LnNiOs formed with the 4f elenients have the perovskite structure, while NiCrOs has a statistical corundum structure it is concluded from the magnetic properties that this compound contains high-spin Ni(iii). ... 

Oxides play many roles in modem electronic technology from insulators which can be used as capacitors, such as the perovskite BaTiOs, to the superconductors, of which the prototype was also a perovskite, Lao.sSro CutT A, where the value of x is a function of the temperature cycle and oxygen pressure which were used in the preparation of the material. Clearly the chemical difference between these two materials is that the capacitor production does not require oxygen partial pressure control as is the case in the superconductor. Intermediate between these extremes of electrical conduction are many semiconducting materials which are used as magnetic ferrites or fuel cell electrodes. The electrical properties of the semiconductors depend on the presence of transition metal ions which can be in two valence states, and the conduction mechanism involves the transfer of electrons or positive holes from one ion to another of the same species. The production problem associated with this behaviour arises from the fact that the relative concentration of each valence state depends on both the temperature and the oxygen partial pressure of the atmosphere. 

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