Scandium hydrated salts

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. 

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. 

Other hydrated salts include Sc2 (C2 04)3-61120, Sc (N03)3-4H20, and Sc2(S04)3-5H20 the structure of the oxalate shows approximately dodecahedral coordination of scandium by two water molecules and six oxygens from bridging oxalates. The oxalate is, unlike lanthanide oxalates, slightly soluble in water and also dissolves in excess oxalate as 80(0204)2. No structural data are available for the nitrate, although it should be noted that eight-coordinate Sc(N03)3(H20)2 and nine-coordinate Sc(N03)3(H20)3 molecules are present in crown ether... 

Preparative Methods scandium triflate is commercially available. On the other hand, it can also be prepared from the corresponding oxide (SC2O3) and aqueous trifluoromethanesulfonic acid (TfOH). After filtration and concentration of the clear aqueous solution in vacuo, the resulting hydrated salt is dried in vacuo (< 1 mmHg) at 200 °C for 40 h to afford the anhydrous triflate, which is stored over P2O5. 

IR spectra, 469 soils, 962 structure, 471 Salt hydrates, 296 Samarium(III) complexes salicylic acid crystal structure, 481 Sapphyrins, 888 demetallation, 891 metallation, 891 reactions, 891 synthesis, 889 Scandium reactions... 

Partial hydrolysis of the aqua ion produces a bridged dimeric species, the [(H20)5Sc(0H)2Sc(H20)5]" + ion, which has been found in three salts, [(H20)5Sc(/u.-0H)2Sc(H20)s] X4 2H2O (X = Cl, Br), and also a benzene sulfonate [(H20)5Sc(/x-0H)2Sc(H20)5] (C6H5S03)4-4H20. In view of the tendency of many of the hydrated lanthanide halides to contain coordinated halide ions, the chlorides in particular, the absence of halide from the coordination sphere of scandium in these compounds is remarkable. 

The family of rare earths as described in this chapter consists of the elements in the lanthanide series plus scandium and yttrium. Formula representations of rare earth salts refer to the most common hydration state unless spedfically noted otherwise. 

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