User:Praseodymium-141/Holmium compounds

Holmium compounds are compounds formed by the element holmium (Ho). Holmium usually forms compounds in the +3 oxidation state, although compounds with holmium in the +2, +1 and 0 oxidation states are known.

Oxides and chalcogenides


Holmium(III) oxide is the only oxide of holmium. It changes its apparent color depending on the lighting conditions. In daylight, it has a tannish yellow color. Under trichromatic light, it appears orange red, almost indistinguishable from the appearance of erbium oxide under the same lighting conditions. The perceived color change is related to the sharp emission lines of trivalent holmium ions acting as red phosphors.

Other chalcogenides are known for holmium. Holmium(III) sulfide has orange-yellow crystals in the monoclinic crystal system, with the space group P21/m (No. 11). Under high pressure, holmium(III) sulfide can form in the cubic and orthorhombic crystal systems. It can be obtained by the reaction of holmium(III) oxide and hydrogen sulfide at 1325 °C. Holmium(III) selenide is also known. It is antiferromagnetic below 6 K.

Halides
All four trihalides of holmium are known. Holmium(III) fluoride is a yellowish powder that can be produced by reacting holmium(III) oxide and ammonium fluoride, then crystallising it from the ammonium salt formed in solution. Holmium(III) chloride can be prepared in a similar way, with ammonium chloride instead of ammonium fluoride. It has the YCl3 layer structure in the solid state. These compounds, as well as holmium(III) bromide and holmium(III) iodide, can be obtained by the direct reaction of the elements:


 * 2 Ho + 3 X2 → 2 HoX3

In addition, holmium(III) iodide can be obtained by the direct reaction of holmium and mercury(II) iodide, then removing the mercury by distillation.

Organoholmium compounds
Organoholmium compounds are very similar to those of the other lanthanides, as they all share an inability to undergo π backbonding. They are thus mostly restricted to the mostly ionic cyclopentadienides (isostructural with those of lanthanum) and the σ-bonded simple alkyls and aryls, some of which may be polymeric.