Thorium nitrate
| Identifiers | |
|---|---|
| ECHA InfoCard | 100.034.090 |
| Properties | |
| Th(NO3)4 | |
| Molar mass | 480.066 (anhydrous) 552.130 (tetrahydrate) 570.146 (pentahydrate) 588.162 (hexahydrate) |
| Appearance | Colorless crystal |
| Melting point | 55 |
| Boiling point | dec. |
| Soluble | |
| Hazards | |
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EU classification (DSD) (outdated)
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox references | |
Thorium(IV) nitrate is a chemical compound with the formula Th(NO3)4, which is hydroscopic and radioactive.
Thorium(IV) nitrate hydrate can be prepared by the reaction of thorium(IV) hydroxide and nitric acid:
Different hydrates are produced by crystallizing in different conditions. When a solution is very dilute, the nitrate is hydrolysed. Although various hydrates have been reported over the years, and some suppliers even claim to stock them, only the tetrahydrate and pentahydrate actually exist. What is called a hexahydrate, crystalized from a neutral solution, is probably a basic salt.
The pentahydrate is the most common form. It is crystallized from dilute nitric acid solution.
The tetrahydrate, Th(NO3)4•4H2O is formed by crystallizing from a stronger nitric acid solution Concentrations of nitric acid from 4 to 59% result in the tetrahydrate forming. The thorium atom has 12 coordination, with four bidentate nitrate groups and four water molecules attached to each thorium atom.
To obtain the anhydrous thorium(IV) nitrate, thermal decomposition of Th(NO3)4·2N2O5 is required. The decomposition occurs at 150-160 °C.
Anhydrous thorium nitrate is a white substance. It is covalently bound with low melting point of 55 °C.
The pentahydrate Th(NO3)4•5H2O crystallizes with clear colourless crystals in the orthorhombic system. The unit cell size is a=11.191 b=22.889 c=10.579 Å. Each thorium atom is connected twice to each of four bidentate nitrate groups, and to three, and to three water molecules via their oxygen atoms. In total the thorium is eleven-coordinated. There are also two other water molecules in the crystal structure. The water is hydrogen bonded to other water, or to nitrate groups. The density is 2.80 g/cm3. Vapour pressure of the pentahydrate at 298K is 0.7 torr, and increases to 1.2 torr at 315K, and at 341K it is up to 10.7 torr. At 298.15K the heat capacity is about 114.92 calK−1mol−1. This heat capacity shrinks greatly at cryogenic temperatures. Entropy of formation of thorium nitrate pentahydrate at 298.15K is −547.0 calK−1mol−1. The standard Gibbs energy of formation is −556.1 kcalmol−1.
Thorium nitrate can dissolve in several different organic solvents including alcohols, ketones, esters and ethers. This can be used to separate different metals such as the lanthanides. With ammonium nitrate in the aqueous phase, thorium nitrate prefers the organic liquid, and the lanthanides stay with the water.
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