Cadmium iodide

Crystal structure
__ Cd 2+      __ I -
General
Surname	Cadmium iodide
other names	Cadmium (II) iodide Cadmium diiodide
Ratio formula	CdI 2
Brief description	colorless to dark brown, shiny, odorless hexagonal leaflets
External identifiers / databases
CAS number 7790-80-9 EC number 232-223-6 ECHA InfoCard 100.029.294 PubChem 24635 Wikidata Q425252
properties
Molar mass	366.22 g mol −1
Physical state	firmly
density	5.67 g cm −3 (30 ° C)
Melting point	387 ° C
boiling point	796 ° C
solubility	very light in water (1850 g l −1 at 20 ° C)
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 301 + 331-351-373-410 P: 260-280-301 + 330 + 331 + 310-304 + 340 + 311-403 + 233
MAK	repealed as carcinogenic
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Cadmium iodide , CdI ₂ , is a chemical compound of cadmium and iodine . It crystallizes in a layer structure in the hexagonal crystal system. The cadmium iodide structure gives its name to a number of other compounds that crystallize in the same structure.

Extraction and presentation

The production of cadmium iodide succeeds from the elements at elevated temperature.

${\displaystyle \mathrm {Cd+I_{2}\longrightarrow CdI_{2}} }$

It can also be prepared by dissolving cadmium or cadmium carbonate in hydriodic acid and then crystallizing it. This creates a hydrate that is dehydrated with thionyl chloride and can thus be converted into anhydrous cadmium iodide.

Production by reacting cadmium sulfate with potassium iodide is also possible .

${\displaystyle \mathrm {CdSO_{4}+2\ KI\longrightarrow CdI_{2}+K_{2}SO_{4}} }$

properties

Cadmium iodide forms stable, white, shiny, hexagonal platelets in air, which can be easily split due to the layer structure.

Cadmium iodide crystallizes in a hexagonal crystal structure in the space group P 6 ₃ mc (space group no.186) with the lattice parameters a = 425  pm and c = 1367 pm as well as two formula units per unit cell (4H structure according to the Ramsdell classification) or in one slightly less stable trigonal structure with the space group P 3 m 1 (No. 164) and the lattice parameters a = 424.4 pm and c = 685.9 pm (2H structure). The iodide ions form a hexagonal closest packing of spheres , in which every second octahedral gap ^layer is completely occupied with cadmium ions Cd ²⁺ . The cadmium ions are octahedral surrounded by six iodide ions, whereby each iodide ion forms the tip of a trigonal pyramid with three cadmium ions as a base (coordination = 6: 3). There are individual layers of cadmium iodide that are only held together by weak van der Waals forces . In one of the cadmium iodide structures, bromides and iodides in particular crystallize , but also some sulphides , selenides or tellurides such as magnesium bromide , calcium iodide , iron (II) iodide , tin (IV) sulphide or titanium (IV) sulphide . In addition to the two forms mentioned, over 250 other polytypes of cadmium iodide are known, which differ in the sequence of the layers.

A relatively newly discovered modification of cadmium iodide are the well-characterized nanoparticles that CdI _{2 forms} when irradiated with electrons, creating nanotubes and fullerene- like structures.

Compounds of the CdI ₂ type

Cadmium iodide belongs, like many other halides and hydroxides of divalent metals or sulfides and tellurides of tetravalent metals for CdI ₂ - structure type , all of a crystal structure of the simplest polytypes comprise:

Members

• CdI ₂ , MgI ₂ , TiI ₂
• MgBr ₂ , TiBr ₂ , CdBr ₂
• TiCl ₂ , VCl ₂
• Mg (OH) ₂ , Ni (OH) ₂ , Ca (OH) ₂
• TiS ₂ , ZrS ₂ , TiSe ₂ , SiTe ₂ ,
• Ag ₂ F and W ₂ C belong to the anti-CdI ₂ type with large metal cations on the iodide positions, while the anions occupy the octahedral holes.

use

Cadmium iodide is used as a reagent for the detection of alkaloids and nitrous acid as well as in the production of luminous paints and electrolysis cadmium. It is also used in photographic processes such as ferrotype .

safety instructions

Cadmium iodide is toxic when inhaled and swallowed, has chronic toxicity and is carcinogenic in animal experiments. The lethal dose LD ₅₀ in mice is 166 mg / kg. The lowest known lethal dose for oral ingestion by humans (LD _Lo ) is given as 81 mg / kg. In addition, the eco-toxicity of cadmium iodide is very high, especially for aquatic organisms, especially since it can cause long-term damage in water.

Individual evidence

1. ↑ ^{a b c d e f g h} Entry on cadmium iodide in the GESTIS substance database of the IFA , accessed on January 8, 2018(JavaScript required) .
2. ↑ Entry on cadmium iodide in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
3. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 1490.
4. ↑ Georg Brauer (Ed.), With the collaboration of Marianne Baudler a . a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume II, Ferdinand Enke, Stuttgart 1978, ISBN 3-432-87813-3 , p. 1043.
5. ↑ ^{a b} entry on cadmium iodide. In: Römpp Online . Georg Thieme Verlag, accessed on June 16, 2014.
6. ↑ P. Villars, K. Cenzual: Structure types. Part 4: Space Groups (189) - (174). In: Landolt-Börnstein - Group III Condensed matters, Springer, Berlin 2006.
7. ↑ LS Ramsdell: Studies on silicon carbide . In: American Mineralogist , 32, 1947, pp. 64-82, PDF .
8. ↑ YM DeHaan: Structure refinements, thermal motion and Madelung constants of cadmium iodide and cadmium hydroxide-type layer structures. In: National Bureau of Standards (US), Special Publication, 1969, pp. 233-236.
9. ↑ Erwin Riedel, Christoph Janiak: Inorganic Chemistry . 7th edition. 2007, de Gruyter, ISBN 978-3-11-018903-2 , p. 138.
10. ↑ H. Kaur: Growth and formation of polytypes in crystals of cadmium iodide. In: Archives of Applied Science Research , 6 (1), 2014, pp. 64-66.
11. ↑ R. Popovitz-Biro, N. Sallacan, R. Tenne: Cdl ₂ nanoparticles with closed-cage (fullerene-like) structures. In: J. Mater. Chem. 2003, 13, pp. 1631-1634, doi : 10.1039 / b302505e .
12. ↑ Entry on cadmium iodide in the ChemIDplus database of the United States National Library of Medicine (NLM) .