Zinc iodide

Crystal structure
__ Zn 2+      __ I -
General
Surname	Zinc iodide
other names	Zinc (II) iodide
Ratio formula	ZnI 2
Brief description	white odorless solid
External identifiers / databases
CAS number 10139-47-6 EC number 233-396-0 ECHA InfoCard 100.030.347 PubChem 66278 Wikidata Q204828
properties
Molar mass	319.18 g mol −1
Physical state	firmly
density	4.74 g cm −3
Melting point	446 ° C
boiling point	625 ° C
solubility	very soluble in water (4500 g l −1 at 20 ° C) easily soluble in ethanol and diethyl ether
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 314-410 P: 273-280-302 + 352-305 + 351 + 338-310-501
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Zinc iodide is a chemical compound of zinc and iodine from the group of halides . The white hygroscopic powder absorbs water in moist air and dissolves ( dissolves ). In air it reacts to release iodine, so that the compound or its solution turns yellowish.

Extraction and presentation

Zinc iodide can be obtained by reacting zinc with iodine with the addition of water.

${\displaystyle \mathrm {Zn+I_{2}\rightarrow ZnI_{2}} }$

properties

Zinc (II) iodide is a colorless solid that is soluble in water, ethanol, ether, acetone and dioxane. The dihydrate crystallizes out of the solution below 0 ° C. It decomposes when heated in air.

The crystalline structure of zinc (II) iodide is unusual. Like the other zinc halides (with the exception of zinc fluoride ), it does not form an ionic bond , but a covalent bond and is therefore not a salt in the strict sense of the word. While the zinc atoms are tetrahedronically coordinated as in zinc chloride , in contrast to this, four tetrahedra connected at three corners form a “super tetrahedron” with the composition (Zn ₄ I ₁₀ ) and thus a corresponding three-dimensional structure. These “super tetrahedra” resemble the structure of phosphorus pentoxide P ₄ O ₁₀ . Molecular zinc (II) iodide is linear according to the VSEPR model and has a Zn – I distance of 238 pm.

use

Since the compound absorbs X-rays well, it is often used as a contrast medium in X-ray diagnostics of materials (penetration into damaged material). It is also used as a school chemical in experiments on electrolysis .

By utilizing this reaction and its reversal, the construction of a zinc-iodine accumulator is also possible.

Individual evidence

1. ↑ ^{a b c d e} Zinc iodide data sheet (PDF) from Merck , accessed on April 25, 2011.
2. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Properties of the Elements and Inorganic Compounds, pp. 4-100.
3. ↑ ^{a b} Entry on zinc iodide in the GESTIS substance database of the IFA , accessed on January 8, 2020(JavaScript required) .
4. ↑ ^{a b} Georg Brauer (Ed.), With the collaboration of Marianne Baudler u a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume II, Ferdinand Enke, Stuttgart 1978, ISBN 3-432-87813-3 , p. 1025.
5. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 .
6. ^ ^{A b c} A. F. Wells: Structural Inorganic Chemistry. 5th edition, Oxford Science Publications, 1984, ISBN 0-19-855370-6 .
7. ↑ Electrolysis of zinc iodide (PDF; 217 kB).
8. ↑ Zinc-iodine element (Poenitz-net) (PDF; 13 kB).