Scandium compounds

Ionic radii (pm)

Al	Sc	Y	La	Lu
53.5	74.5	90.0	103.2	86.1

Scandium compounds are compounds containing the element scandium. The chemistry of scandium is almost completely dominated by the trivalent ion, Sc³⁺, due to its electron configuration, [Ar] 3d¹4s². The radii of M³⁺ ions in the table below indicate that the chemical properties of scandium ions have more in common with yttrium ions than with aluminium ions. In part because of this similarity, scandium is often classified as a lanthanide-like element.

+3 oxidation state

Oxides and hydroxides

The oxide

α- and γ-ScOOH are isostructural with their aluminium hydroxide oxide counterparts.^[2] Solutions of Sc³⁺
in water are acidic due to hydrolysis.

Halides and pseudohalides

The halides ScX₃, where X= Cl, Br, or I, are very soluble in water, but ScF₃ is insoluble. In all four halides, the scandium is 6-coordinated. They can be prepared by reacting scandium oxide or scandium hydroxide with the corresponding acid:^[3]

Sc(OH)₃ + 3 HX → ScX₃ + 3 H₂O

The halides are

Compounds that feature scandium in oxidation states other than +3 are rare but well characterized. The blue-black compound CsScCl₃ is one of the simplest. This material adopts a sheet-like structure that exhibits extensive bonding between the scandium(II) centers.[4] Scandium hydride is not well understood, although it appears not to be a saline hydride of Sc(II).^[5] As is observed for most elements, a diatomic scandium hydride has been observed spectroscopically at high temperatures in the gas phase.^[6] Scandium borides and carbides are non-stoichiometric, as is typical for neighboring elements.^[7]

Lower oxidation states (+2, +1, 0) have also been observed in organoscandium compounds.^{[8][9][10][11]}

Organic derivatives

Scandium forms a series of organometallic compounds with

• Yttrium compounds
• Titanium compounds

References