Scandium hydration

Scandium, Sc, which was first isolated in 1937, is a reactive metal it reacts with water about as vigorously as calcium does. It has few uses and is not thought to be essential to life. The small, highly charged Sc3+ ion is strongly hydrated in water (like Al3+), and the resulting Sc(H2())6]3+ complex is about as strong a Bronsted acid as acetic acid. 

Hproblems associated with all the trihalides of this review of the presence of small amounts of hydrates or oxochlorides. While on the matter of possible impurities, it may be recalled that in Bommer and Hohmann s early work there is a discrepancy between enthalpies of solution of anhydrous trichlorides and of respective metals in hydrochloric acid. Here the more likely impurity to be responsible is unreacted potassium metal in the lanthanide metal used in the hydrochloric acid dissolution experiments. 

The enthalpies of solution and solubilities reviewed here provide much of the experimental information required in the derivation of single-ion hydration and solvation enthalpies, Gibbs free energies, and entropies for scandium, yttrium, and lanthanide 3+ cations. 

The hexameric scandium decanoate extracted in benzene is different from the hexameric Al(III), Ga(III), and In(III) decanoates in that the former is neither hydrated nor hydrolyzed (154). Galkina and Strel tsova (36), in the butanoic acid/iso-butanol system, attempted to separate Sc from rare earths and the other metals. They proposed the monomeric Sc(III) butanoate, ScA3, as the extracted species. In this extraction system, the polymerization of scandium butanoate in the organic phase seems to be prevented by solvation with iso-butanol. In the study of the synergistic effect of various amines on the extraction of lanthanum and scandium with hexanoic and a-bromohexanoic acids in chloroform, Sukhan et al. (138) proposed LaA3(HA)3 and ScA3(HA)3 as the extracted species. 

All four scandium(III) halides are known, all but the fluoride (WO3 structure) having the FeCfr structure. They can be obtained as white solids directly from the elements and in some cases by dehydration of the hydrated salts, as well as by thermal decomposition of (NH4)3ScX6 (X = Cl, Br), a method also used for the lanthamdes. Gas-phase studies have identified isolated planar SCF3 molecules at 1750K ScCfr molecules with a very slight pyramidal distortion and both monomers and dimers in Scfr vapour at 1050 K. 

Ripert, V., Hubert-Pfalzgraf, L.G., and Vaissermann, J. (1999) Dehydration of scandium chloride hydrate synthesis and molecular structures of ScCl3(r -DME)(MeCN), ScCL (diglyme) and [Sc2 (p-OH)2(H20)io]Cl4-2H20. Po/yAerfron, 18, 1845-1851. 

A recent synthesis of anhydrous 80(0104)3 from hydrated scandium chloride proceeds via an orange adduct [Sc(C104)3-0.25Cl206] that loses the CI2O6 in vacuo at 95 °C (see Scheme (2)). 

Grey anhydrous scandium triflate, [Sc(03SCF3)3] (triflate = trifluoromethane sulfonate), has been obtained by dehydration of the hydrate at 190 200 °C the hydrated salt was itself obtained from the reaction of hydrated scandium chloride and dilute triflic acid. [Sc(03SCF3)3], in which triflate is believed to act as a bidentate ligand (similar to perchlorate in 80(004)3), is not isomorphous with the lanthanide analogues. 

It was only in 1995 that the first structure of a hydrated salt of scandium containing only water molecules in its coordination sphere was reported. Refluxing scandium oxide with triflic acid leads to the isolation of hydrated scandium triflate Sc(03SCF3)3 9H20. It is isomorphous with the hydrated lanthanide triflates, containing tricapped trigonally prismatic coordinate scandium in the [Sc(H20)g] ions, with Sc—O (vertices) = 2.171(9) A and Sc—O (face capped) 2.47(2) A. 

The crystal structure of the hydrated scandium triflate has been determined. Nine water molecules surround the scandium ion and the triflate anions are hydrogen bonded to the water molecules.206 A structural analysis of anhydrous scandium triflate, using X-ray powder diffraction and IR spectroscopy, indicates that the triflate acts as a bidentate ligand with scandium in an octahedral environment.207... 

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