User:Praseodymium-141/Praseodymium compounds

Oxides
Praseodymium can form oxides in many different ways, although the only oxides that are stable at room temperature are Pr2O3, Pr6O11 and PrO2. Praseodymium(III) oxide is a green powder that forms hexagonal crystals, and crystallizes in the manganese(III) oxide or bixbyite structure. Praseodymium(IV) oxide can be produced by boiling Pr6O11 in water or acetic acid:


 * Pr6O11 + 3 H2O → 4 PrO2 + 2 Pr(OH)3

Praseodymium(III,IV) oxide is the most stable form of the praseodymium oxides at ambient temperature and pressure. It is soluble in water and has a cubic fluorite structure. It can be prepared via solid-state methods such as thermolysis, molten salt method, calcination or precipitation.



In addition to Pr6O11, praseodymium also forms a system of oxides at different phases:

Halides


Praseodymium metal reacts with all the stable halogens to form green trihalides:
 * 2 Pr (s) + 3 F2 (g) → 2 PrF3 (s)
 * 2 Pr (s) + 3 Cl2 (g) → 2 PrCl3 (s)
 * 2 Pr (s) + 3 Br2 (g) → 2 PrBr3 (s)
 * 2 Pr (s) + 3 I2 (g) → 2 PrI3 (s)

Praseodymium(III) fluoride is the most stable fluoride of praseodymium. It can be prepared the reaction between praseodymium(III) nitrate and sodium fluoride will produce praseodymium(III) fluoride as a green crystalline solid. Praseodymium(III) chloride is a light green solid that can be prepared by treating praseodymium metal with hydrogen chloride. It is usually purified by vacuum sublimation. Praseodymium(III) chloride is Lewis acidic, classified as "hard" according to the HSAB concept. Rapid heating of the hydrate may cause small amounts of hydrolysis. PrCl3 forms a stable Lewis acid-base complex K2PrCl5 by reaction with potassium chloride; this compound shows interesting optical and magnetic properties.

Praseodymium(III) bromide is the only stable bromide of praseodymium. It adopts the UCl3 crystal structure. The praseodymium ions are 9-coordinate and adopt a tricapped trigonal prismatic geometry. The praseodymium–bromine bond lengths are 3.05 Å and 3.13 Å. Praseodymium(III) iodide can be prepared by heating praseodymium and iodine in an inert atmosphere produces praseodymium(III) iodide, or by heating praseodymium with mercury(II) iodide. It forms orthorhombic crystals which are hygroscopic. It crystallizes in the PuBr3 type with space group Cmcm (No. 63) with a = 4.3281(6) Å, b = 14.003(6) Å and c = 9.988(3) Å.

The tetrafluoride, PrF4, is also known, and is produced by reacting a mixture of sodium fluoride and praseodymium(III) fluoride with fluorine gas, producing Na2PrF6, following which sodium fluoride is removed from the reaction mixture with liquid hydrogen fluoride. Additionally, praseodymium forms a bronze diiodide; like the diiodides of lanthanum, cerium, and gadolinium, it is a praseodymium(III) electride compound.