Scandium lower oxidation states

In anaerobic soils, the individual chemistry of the ions is more distinctive. The transition metal ions in the middle of each period of the periodic table—chromium, manganese, iron, nickel, cobalt, and copper—can reduce to lower oxidation states, while the end members—scandium, titanium, and zinc—have only one oxidation state. The lower oxidation states are more water soluble but still tend to precipitate as carbonates and sulfides, or associate with organic matter, thus reducing their movement but increasing then plant availability. 

Scandium at the beginning of the first row of the d-block and zinc at the end only exhibit one stable oxidation state in their compounds, +3 (Sc ) and +2 (Zn ), respectively. Notice that the lower oxidation states correspond to simple or atomic ions, for example, Mn (+2), while the higher oxidation states correspond to covalently bonded oxoanions, for example, Mn04 (+7). 

In the specific case of scandium, mono- and mixed-valence species can also be isolated together with divalent complexes for instance, a Sc organometallic compoimd could be obtained imder relatively mild conditions. Finally, the author describes the few knovm zerovalent bis(arene) rare-earth complexes which have been obtained by co-condensation of arenes or heteroarenes with metal vapors. In his conclusion, F. Nief notes that the low-valence molecular chemistry of rare earths, which was once thought to be restricted to divalent samarium, europium, and ytterbium, has been extended to several other rare earths, as well as to lower valence oxidation states. It is the opinion of the author that this research area is likely to find fascinating developments in a near future. 

Electrical properties of thin rare earth oxide film have also been studied. The conductivity of praseodymium thin film oxide was measured as a function of temperature and oxygen pressure [9]. The oxide film was found to act as a p-type conduction at temperatures high than 630°C and was a n-type semiconductor at the temperatures of 400-630°C. Thermally evaporated EU2O3 thin film on a glass substrate is also obtained in an amorphous state. From the measurement of frequency dependence of the ac conductance, the predominant mechanism could be ascribed to the result of a hopping type. The ac conductivity measurements were also carried out for thin film of SC2O3 at temperatures between 4 and 295 K [10]. The conductivity was found to obey the relationship of ai(ffl)=Aco which depends on frequency and s is dependent on temperature and is a little lower than unity. By using a classical hop mechanism between randomly distributed localized states, a model was proposed and applied to scandium oxide with the assumption that the localized states are caused by lattice vacancies. The model is expected to be... 

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