: Scandium compounds are compounds containing the element

scandium Scandium is a chemical element with the symbol Sc and atomic number 21. It is a silvery-white metallic d-block element. Historically, it has been classified as a rare-earth element, together with yttrium and the Lanthanides. It was discovere ...

. The chemistry of scandium is almost completely dominated by the trivalent ion, Sc³⁺, due to its

electron configuration In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals. For example, the electron configuration of the neon at ...

, r3d¹4s². 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 and the hydroxide are

amphoteric In chemistry, an amphoteric compound () is a molecule or ion that can react both as an acid and as a base. What exactly this can mean depends on which definitions of acids and bases are being used. One type of amphoteric species are amphip ...

: : + 3 → (scandate ion) : + 3 + 3 → α- and γ-ScOOH are isostructural with their aluminium hydroxide oxide counterparts. Solutions of in water are acidic due to

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis ...

Halides and pseudohalides

The

halide In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a f ...

s , where X= Cl, Br, or I, are very soluble in water, but is insoluble. In all four halides, the scandium is 6-coordinated. The halides are

Lewis acids A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...

; for example, dissolves in a solution containing excess fluoride ion to form . The coordination number 6 is typical for Sc(III). In the larger Y³⁺ and La³⁺ ions,

coordination number In chemistry, crystallography, and materials science, the coordination number, also called ligancy, of a central atom in a molecule or crystal is the number of atoms, molecules or ions bonded to it. The ion/molecule/atom surrounding the central i ...

s of 8 and 9 are common.

Scandium triflate Scandium trifluoromethanesulfonate, commonly called scandium triflate, is a chemical compound with formula Sc(SO3CF3)3, a salt consisting of scandium cations Sc3+ and triflate anions. Scandium triflate is used as a reagent in organic chemistry ...

is sometimes used as a

Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...

catalyst in

organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clay ...

Other oxidation states

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

non-stoichiometric In chemistry, non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); mo ...

, as is typical for neighboring elements.Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. . Lower oxidation states (+2, +1, 0) have also been observed in organoscandium compounds.

Organic derivatives

Scandium forms a series of organometallic compounds with

cyclopentadienyl Cyclopentadienyl can refer to * Cyclopentadienyl anion, or cyclopentadienide, **Cyclopentadienyl ligand A cyclopentadienyl complex is a coordination complex of a metal and cyclopentadienyl anion, cyclopentadienyl groups (, abbreviated as Cp−) ...

ligands (Cp), similar to the behavior of the lanthanides. One example is the chlorine-bridged dimer, and related derivatives of

pentamethylcyclopentadienyl 1,2,3,4,5-Pentamethylcyclopentadiene is a cyclic diene with the formula C5Me5H (Me = CH3). 1,2,3,4,5-Pentamethylcyclopentadiene is the precursor to the ligand ''1,2,3,4,5-pentamethylcyclopentadienyl'', which is often denoted Cp* (C5Me5) and read ...

ligands.

References