tailieunhanh - Tetravalent chemistry: Inorganic

Tetravalent chemistry: Inorganic. This chapter gives an overview on the chemistry of tetravalent lanthanide compounds, especially those of tetravalent cerium. Following a brief Introduction it covers the tetrahalides, dioxides and other lanthanides(IV) salts. Coordination compounds of cerium in the oxidation state +4 include halogeno complexes and complexes of oxo acids, β-diketonates and related Schiff-base complexes as well as porphyrinates and related complexes. | The Rare Earth Elements: Fundamentals and Applications eibc2033 Tetravalent Chemistry: Inorganic Farid Mohamed Ahmed and Frank T. Edelmann* Chemisches Institut der Otto-von-Guericke-Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Germany Abstract This chapter gives an overview on the chemistry of tetravalent lanthanide compounds, especially those of tetravalent cerium. Following a brief Introduction it covers the tetrahalides, dioxides and other lanthanides(IV) salts. Coordination compounds of cerium in the oxidation state +4 include halogeno complexes and complexes of oxo acids, β-diketonates and related Schiff-base complexes as well as porphyrinates and related complexes. Introduction Besides the ubiquitous oxidation state Ln3+, the higher oxidation state Ln4+ is also encountered with some lanthanoids, for example in the case of the ions Ce4+ (f0, orange-yellow), Pr4+ (f1, colorless), Nd4+ (f2, blue-violet), Tb4+ (f7, colorless), and Dy4+ (f8, orange-yellow) (Table 1). However, all three states Ln2+,3+,4+ are never encountered for the same element. Thus the highly important mechanistic steps of oxidative addition and reductive elimination typical for the d-block metals cannot occur with the f-block metals as they would involve M2+ or M4+ transformations, Table 1. Possible oxidation states for rare earth metals. Ce Pr Nd Pm +3 +4 +3 +4 +3 +4 +3 Sm +2 +3 Eu +2 +3 Gd Tb Dy Ho Er +3 +3 +4 +3 +4 +3 +3 Tm +2 +3 Yb +2 +3 Lu +3 Among the tetravalent lanthanide ions, only Ce4+ is readily available in aqueous solution (E Ce3+/Ce4+ = + V in 2M H 2 SO 4 , V in 1M HNO 3 , V in 1M HClO 4 ). The different values for the reduction potentials indicate that stable complexes are formed in these acidic media. Thermodynamically, the oxidation of water by the Ce4+ aqua ion should be possible, but the system is kinetically stable. In contrast, the much more positive normal potentials of the other tetravalent lanthanide