22.4B: Yttrium(III) Ion
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As a trivalent transition metal, yttrium forms various inorganic compounds, generally in the oxidation state of +3, by giving up all three of its valence electrons. A good example is yttrium(III) oxide (\(\ce{Y2O3}\)), also known as yttria, a six-coordinate white solid.
Yttrium forms a water-insoluble fluoride, hydroxide, and oxalate, but its bromide, chloride, iodide, nitrate and sulfate are all soluble in water. The \(\ce{Y^{3+}}\) ion is colorless in solution because of the absence of electrons in the d and f electron shells. With halogens, yttrium forms trihalides such as yttrium(III) fluoride (\(\ce{YF3}\)), yttrium(III) chloride (\(\ce{YCl3}\)), and yttrium(III) bromide (\(\ce{YBr3}\)) at temperatures above roughly 200 °C.
\[\ce{2 Y(s) + 3F2 \rightarrow YF3(s)}\]
Similarly, carbon, phosphorus, selenium, silicon and sulfur all form binary compounds with yttrium at elevated temperatures.
Water readily reacts with yttrium and its compounds to form \(\ce{Y2O3}\). Concentrated nitric and hydrofluoric acids do not rapidly attack yttrium, but other strong acids do.
Organoyttrium chemistry is the study of compounds containing carbon-yttrium bonds. They are studied in academic research, but have not received widespread use otherwise. These compounds use \(\ce{YCl3}\) as a starting material, which is in turn obtained in a reaction of \(\ce{Y2O3}\) with concentrated hydrochloric acid and ammonium chloride.
Hapticity is a term to describe the coordination of a group of contiguous atoms of a ligand bound to the central atom; it is indicated by the Greek character eta, \(η\). Yttrium complexes were the first examples of complexes where carboranyl ligands were bound to a d0-metal center through a η7-hapticity. Vaporization of the graphite intercalation compounds graphite–Y or graphite–Y2O3 leads to the formation of endohedral fullerenes such as Y@C82. Electron spin resonance studies indicated the formation of \(\ce{Y^{3+}}\) and (C82)3− ion pairs. The carbides Y3C, Y2C, and YC2 can be hydrolyzed to form hydrocarbons.
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