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| Names | |||
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| Other names Neodymium trichloride | |||
| Identifiers | |||
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3D model (JSmol) | |||
| ChemSpider |
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| ECHA InfoCard | 100.030.016 | ||
| UNII | |||
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| Properties | |||
| NdCl3, NdCl3·6H2O (hydrate) | |||
| Molar mass | 250.598 g/mol | ||
| Appearance | Mauve-colored powder[1] hygroscopic | ||
| Density | 4.13 g/cm3 (2.3 for hydrate)[1] | ||
| Melting point | 759 °C (1,398 °F; 1,032 K)[1] | ||
| Boiling point | 1,600 °C (2,910 °F; 1,870 K)[1] | ||
| 1 kg/L at 25 °C[1] | |||
| Solubility inethanol | 0.445 kg/L | ||
| Structure[2] | |||
| hexagonal (UCl3 type),hP8 | |||
| P63/m, No. 176 | |||
a = 0.73988 nm,c = 0.42423 nm | |||
Formula units (Z) | 2 | ||
| Tricapped trigonal prismatic (nine-coordinate) | |||
| Hazards | |||
| GHS labelling: | |||
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| Warning | |||
| H315,H319,H335 | |||
| P261,P264,P271,P280,P302+P352,P304+P340,P305+P351+P338,P312,P321,P332+P313,P337+P313,P362,P403+P233,P405,P501 | |||
| NFPA 704 (fire diamond) | |||
| Safety data sheet (SDS) | External SDS | ||
| Related compounds | |||
Otheranions | Neodymium(III) bromide Neodymium(III) oxide | ||
Othercations | LaCl3,SmCl3,PrCl3,EuCl3,CeCl3,GdCl3,TbCl3,Promethium(III) chloride | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Neodymium(III) chloride or neodymium trichloride is a chemical compound ofneodymium andchlorine with the formula NdCl3. Thisanhydrous compound is a mauve-colored solid that rapidly absorbs water on exposure to air to form a purple-colored hexahydrate, NdCl3·6H2O. Neodymium(III) chloride is produced from mineralsmonazite andbastnäsite using a complex multistage extraction process. The chloride has several important applications as an intermediate chemical for production of neodymium metal and neodymium-basedlasers and optical fibers. Other applications include a catalyst in organic synthesis and in decomposition of waste water contamination,corrosion protection ofaluminium and itsalloys, andfluorescent labeling of organic molecules (DNA).
NdCl3 is a mauve coloredhygroscopic solid whose color changes to purple upon absorption of atmospheric water. The resulting hydrate, like many other neodymiumsalts, has the interesting property that it appears different colors under fluorescent light- In the chloride's case, light yellow (see picture).[3]
The anhydrous NdCl3 features Nd in a nine-coordinate tricapped trigonal prismatic geometry and crystallizes with theUCl3 structure. Thishexagonal structure is common for many halogenatedlanthanides andactinides such asLaCl3,LaBr3,SmCl3,PrCl3,EuCl3,CeCl3,CeBr3,GdCl3,AmCl3 andTbCl3 but not forYbCl3 andLuCl3.[4]
The structure of neodymium(III) chloride in solution crucially depends on the solvent: In water, the major species are Nd(H2O)83+, and this situation is common for most rare earth chlorides and bromides. Inmethanol, the species are NdCl2(CH3OH)6+ and inhydrochloric acid NdCl(H2O)72+. The coordination of neodymium is octahedral (8-fold) in all cases, but the ligand structure is different.[5]
NdCl3 is a softparamagnetic solid, which turnsferromagnetic at very lowtemperature of 0.5 K.[6] Its electrical conductivity is about 240 S/m andheat capacity is ~100 J/(mol·K).[7] NdCl3 is readily soluble in water and ethanol, but not inchloroform orether. Reduction of NdCl3 with Nd metal at temperatures above 650 °C yieldsNdCl2:[8]
Heating of NdCl3 with water vapors orsilica producesneodymium oxochloride:
Reacting NdCl3 withhydrogen sulfide at about 1100 °C producesneodymium sulfide:
Reactions withammonia andphosphine at high temperatures yieldneodymium nitride andphosphide, respectively:
Whereas the addition ofhydrofluoric acid producesneodymium fluoride:[9]
NdCl3 is produced from mineralsmonazite andbastnäsite. The synthesis is complex because of the low abundance of neodymium in the Earth's crust (38 mg/kg) and because of difficulty of separating neodymium from other lanthanides. The process is however easier for neodymium than for other lanthanides because of its relatively high content in the mineral – up to 16% by weight, which is the third highest aftercerium andlanthanum.[10] Many synthesis varieties exist and one can be simplified as follows:
The crushed mineral is treated with hot concentratedsulfuric acid to produce water-soluble sulfates of rare earths. The acidic filtrates are partially neutralized withsodium hydroxide to pH 3–4.Thorium precipitates out of solution as hydroxide and is removed. After that the solution is treated withammonium oxalate to convert rare earths into their insolubleoxalates. The oxalates are converted to oxides by annealing. The oxides are dissolved innitric acid that excludes the main components,cerium, whose oxide is insoluble in HNO3. Neodymium oxide is separated from other rare-earth oxides byion exchange. In this process, rare-earth ions are adsorbed onto suitable resin by ion exchange with hydrogen, ammonium or cupric ions present in the resin. The rare earth ions are then selectively washed out by suitable complexing agent, such as ammonium citrate or nitrilotracetate.[9]
This process normally yieldsNd2O3; the oxide is difficult to directly convert to elemental neodymium, which is often the goal of the whole technological procedure. Therefore, the oxide is treated withhydrochloric acid andammonium chloride to produce the less stable NdCl3:[9]
The thus produced NdCl3 quickly absorbs water and converts to NdCl3·6H2O hydrate, which is stable for storage, and can be converted back into NdCl3 when necessary. Simple rapid heating of the hydrate is not practical for that purpose because it causeshydrolysis with consequent production of Nd2O3.[11] Therefore,anhydrous NdCl3 is prepared by dehydration of the hydrate either by slowly heating to 400 °C with 4-6 equivalents of ammonium chloride under high vacuum, or by heating with an excess ofthionyl chloride for several hours.[4][12][13][14] The NdCl3 can alternatively be prepared by reacting neodymium metal withhydrogen chloride orchlorine, though this method is not economical due to the relatively high price of the metal and is used for research purposes only. After preparation, it is usually purified by high temperature sublimation under high vacuum.[4][15][16]
Neodymium(III) chloride is the most common starting compound for production of neodymium metal. NdCl3 is heated withammonium chloride orammonium fluoride andhydrofluoric acid or with alkali or alkaline earth metals in vacuum or argon atmosphere at 300–400 °C.
An alternative route iselectrolysis of molten mixture of anhydrous NdCl3 andNaCl, KCl, or LiCl at temperatures about 700 °C. The mixture melts at those temperatures, even though they are lower than the melting points of NdCl3 and KCl (~770 °C).[17]
Although NdCl3 itself does not have strongluminescence,[18] it serves as a source of Nd3+ ions for various light emitting materials. The latter includeNd-YAG lasers and Nd-dopedoptical fiber amplifiers, which amplify light emitted by other lasers. The Nd-YAG laser emitsinfrared light at 1.064 micrometres and is the most popularsolid-state laser (i.e. laser based on a solid medium). The reason for using NdCl3 rather than metallic neodymium or its oxide, in fabrication of fibers is easy decomposition of NdCl3 during thechemical vapor deposition; the latter process is widely used for the fiber grows.[19]
Neodymium(III) chloride is a dopant not only of traditional silica-based optical fibers, but of plastic fibers (dopedphotolime-gelatin,polyimide,polyethylene, etc.) as well.[20] It is also used in as an additive into infraredorganic light-emitting diodes.[21][22] Besides, neodymium doped organic films can not only act as LEDs, but also as color filters improving the LED emission spectrum.[23]
Solubility of neodymium(III) chloride (and other rare-earth salts) is various solvents results in a new type of rare-earth laser, which uses not a solid but liquid as an active medium. The liquid containing Nd3+ ions is prepared in the following reactions:
where Nd3+ is in fact the solvated ion with several selenium oxychloride molecules coordinated in the first coordination sphere, that is [Nd(SeOCl2)m]3+. The laser liquids prepared by this technique emits at the same wavelength of 1.064 micrometres and possess properties, such as high gain and sharpness of the emission, that are more characteristic of crystalline than Nd-glass lasers. The quantum efficiency of those liquid lasers was about 0.75 relative to the traditional Nd:YAG laser.[21]
Another important application of NdCl3 is in catalysis—in combination with organic chemicals, such astriethylaluminium and2-propanol, it acceleratespolymerization of variousdienes. The products include such general purpose synthetic rubbers aspolybutylene,polybutadiene, andpolyisoprene.[11][24][25]
Neodymium(III) chloride is also used to modifytitanium dioxide. The latter is one of the most popular inorganicphotocatalyst for decomposition ofphenol, variousdyes and other waste water contaminants. The catalytic action of titanium oxide has to be activated by UV light, i.e. artificial illumination. However, modifying titanium oxide with neodymium(III) chloride allows catalysis under visible illumination, such as sun light. The modified catalyst is prepared by chemical coprecipitation–peptization method byammonium hydroxide from mixture of TiCl4 and NdCl3 in aqueous solution). This process is used commercially on large scale on 1000 liter reactor for using in photocatalytic self-cleaning paints.[26][27]
Other applications are being developed. For example, it was reported that coating of aluminium or various aluminium alloys produces very corrosion-resistance surface, which then resisted immersion into concentrated aqueous solution of NaCl for two months without sign of pitting. The coating is produced either by immersion into aqueous solution of NdCl3 for a week or byelectrolytic deposition using the same solution. In comparison with traditionalchromium based corrosion inhibitors, NdCl3 and other rare-earth salts are environment friendly and much less toxic to humans and animals.[28][29]
The protective action of NdCl3 on aluminium alloys is based on formation of insoluble neodymium hydroxide. Being a chloride, NdCl3 itself is a corrosive agent, which is sometimes used for corrosion testing of ceramics.[30]
Lanthanides, including neodymium are famous for their brightluminescence and therefore are widely used as fluorescent labels. In particular, NdCl3 has been incorporated into organic molecules, such as DNA, which could be then easily traced using afluorescence microscope during various physical and chemical reactions.[21]
Neodymium(III) chloride does not seem toxic to humans and animals (approximately similar to table salt). TheLD50 (dose at which there is 50% mortality) for animals is about 3.7 g per kg of body weight (mouse, oral), 0.15 g/kg (rabbit, intravenous injection). Mild irritation of skin occurs upon exposure with 500 mg during 24 hrs (Draize test on rabbits).[31] Substances with LD50 above 2 g/kg are considered non-toxic.[32]
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