Scandium chemicals

S. Kobayashi, T. Busujima, S. Nagayama, Scandium Triflate-Catalyzed Strecker-Type Readions of Aldehydes, Amines, and Tributyltin Cyanide in Both Organic and Aqueous Solutions. Achievement of Com-plde Recovery of the Tin Compounds toward Environmentally Friendly Chemical Processes Chem. Commun 1998, 981-982. 

The results in the three preceding subsections conform fairly well to a consistent pattern. However, there are gaps and inconsistencies that require further thermochemical, and in some cases chemical, study. The series of solution enthalpies for the lanthanide trichlorides is satisfactory, but disagreements over the value for the enthalpy of solution of yttrium trichloride in water need resolving, and a modern value for scandium trichloride (at 25°C) would be welcome. The complete absence of enthalpies of solution of tribromides of the lanthanide elements and yttrium is regrettable, as is the lack of a value for scandium triiodide. 

Scandium - the atomic number is 21 and the chemical symbol is Sc. The name derives from the Latin scandia for Scandinavia , where the mineral were found. It was discovered by the Swedish chemist Lars-Fredrik Nilson in 1879 from an ytterbium sample. In the same year, the Swedish chemist Per Theodore Cleve proved that scandium was Mendeleev s hypothetical element eka-boron , whose properties and position in the Period Table Mendeleev had previously predicted. 

Scandium is the first element in the fourth period of the transition elements, which means that the number of protons in their nuclei increases across the period. As with all the transition elements, electrons in scandium are added to an incomplete inner shell rather than to the outer valence shell as with most other elements. This characteristic of using electrons in an inner shell results in the number of valence electrons being similar for these transition elements although the transition elements may have different oxidation states. This is also why all the transition elements exhibit similar chemical activity. 

Although scandium is chemically similar to rare-earths, it no longer is considered to be one of them. Scandium is the 42nd most abundant element found in the Earths crust, making up about 0.0025% of the Earths crust. It is widely distributed at 5 ppm on the Earth. (It is about as abundant as lithium, as listed in group 1.) Scandium is even more prevalent in the sun and several other stars than it is on Earth. 

The chemical properties of yttrium are more similar to those of rare earths than to scandium. However, unlike the rare earths, yttrium exhibits only one valence state, -i-3. 

Scandium(lll) trifluoromethanesulfonate [Sc(OTf)3] was purchased from Aldrich Chemical Company, Inc., (99% purity) and used without additional purification. 

The first blank was filled in 1875. A French chemist discovered an element—gallium—that had all the properties Mendeleyev predicted for the space below aluminum. In 1879, a Swedish researcher discovered scandium, which looked and acted exactly how Mendeleyev said it would in its place below boron. In 1886, a German scientist discovered germanium, the element below silicon. Its chemical properties were almost exactly what Mendeleyev had predicted. 

Table 1 shows the assignment of the various lanthanide elements in the numbering of the compounds in this article. As usual, scandium and yttrium have been included because of their chemical similarity with the lanthanides. Not included was the radioactive promethium for which no complex containing heteroallylic ligands has so far been reported. 

Synthetic strategies to alkoxide complexes have been covered in full by previous reviews [14]. The silylamide route proved to be an advantageous method of preparation, especially in the case of homoleptic derivatives [15]. The group (IIIA) elements - scandium, yttrium and lanthanum - are considered as lanthanides on the basis of their general chemical similarity to the true lanthanides. 

Crystal field theory is one of several chemical bonding models and one that is applicable solely to the transition metal and lanthanide elements. The theory, which utilizes thermodynamic data obtained from absorption bands in the visible and near-infrared regions of the electromagnetic spectrum, has met with widespread applications and successful interpretations of diverse physical and chemical properties of elements of the first transition series. These elements comprise scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel and copper. The position of the first transition series in the periodic table is shown in fig. 1.1. Transition elements constitute almost forty weight per cent, or eighteen atom per cent, of the Earth (Appendix 1) and occur in most minerals in the Crust, Mantle and Core. As a result, there are many aspects of transition metal geochemistry that are amenable to interpretation by crystal field theory. 

While basis sets composed of a sufficient number of s- and p-type functions will yield the Hartree-Fock results for atoms up to scandium,53 such s-p saturated sets are not suitable for molecular SCF calculations. Instead, the basis sets must be augmented with polarizing functions, i.e. those functions, p for hydrogen and d and / for first- and second-row atoms, which are absent in the description of the isolated atoms, but whose presence is essential for a proper description of the distortions in the charge distribution caused by chemical bonding. As the examples in the following section illustrate, the inclusion of polarizing functions in the basis set is essential in the calculation of potential surfaces. 

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