Transition metal ions separation

For a solid-state chemist, it is possible to synthesize compounds with polyhedra containing transition-metal ions separated by diamagnetic elements. By cationic substitution, the following arrangements can be obtained ... 

Figure 5. Schematic Diagrams for Transition Metal Ion Separations in Competitive Transport of Co(II), Cu(II), Ni(II), and Zn(II) Across Emulsion Liquid Membranes by a) Cyanex 272 and b) Di-(p-alkylphenyl)phosphoric Acids.

IR spectroscopy of adsorbed carbon monoxide has been used extensively to characterize the diluted, reduced Cr/silica system [48-54,60,76,77]. CO is an excellent probe molecule for Cr(ll) sites because its interaction is normally rather strong. The interaction of CO with a transition metal ion can be separated into electrostatic, covalent a-dative, and 7r-back donation contributions. The first two cause a blue shift of the vco (with respect to that of the molecule in the gas phase, 2143 cm ), while the last causes a red shift [83-89]. From a measurement of the vco of a given Cr(II) carbonyl complex, information is thus obtained on the nature of the Cr(II)- CO bond. 

A survey of crystal structures of 29 compounds (Table 8), in which the alkyl hydroperoxide anions serves as ligand to metal ions, transition metal ions or group 13-17 elements, provides a mean 0—0 bond length of 1.46 0.03 A, an O—O—C angle of 109 2.1° and a M—O—O angle of 112 6.9°. More specialized aspects that deserve to be addressed separately refer to the nature of the M—O bond, the magnitude of the dihedral angle M—O—O—C and the tetrahedral distortion of the peroxide bound C atom. 

For later discussions it is important to consider what happens if one of the d-orbitals (eg or t2g) is not full (e.g. CoO with seven electrons per atom or TiCl3 with one). The d-orbital is now degenerate, and the orbital motion is no longer quenched. Consider the case of a transitional-metal ion in the d1 state. Suppose that the spins are parallel to the z-axis the spin-orbit coupling will separate the orbitals into functions of the forms... 

It has been pointed out by Reisfeld (8, 9) that the value of h obtained for a vitreous medium depends upon the particular s ion used for the spectral determination. This variation arises owing to the incomplete separation of h and m and is also observed for transition metal ions. The variation, however, is fairly small, but nevertheless was recognised as an initial difficulty in tackling the problem of basicity in oxide-containing media (70). To overcome the problem, the Lewis basicity of an oxide-containing medium was expressed as a ratio of h parameters where... 

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