Hexaiodobenzene

Hexaiodobenzene is an aryl iodide and a six-substituted iodobenzene with the formula C₆I₆. Structurally, it is a derivative of benzene, in which all hydrogen atoms are replaced by iodine atoms. It forms orange crystals^[1] that are poorly soluble in all solvents. It adopts the expected structure with a central C₆ ring.^[3]

Hexaiodobenzene

Names
Preferred IUPAC name Hexaiodobenzene
Other names Periodobenzene
Identifiers
CAS Number	608-74-2
3D model (JSmol)	Interactive image
ChemSpider	11360
ECHA InfoCard	100.009.246
PubChem CID	11853
UNII	L3RDK4VNA8 Y
CompTox Dashboard (EPA)	DTXSID5060562
InChI InChI=1S/C6I6/c7-1-2(8)4(10)6(12)5(11)3(1)9 Key: QNMKKFHJKJJOMZ-UHFFFAOYSA-N InChI=1/C6I6/c7-1-2(8)4(10)6(12)5(11)3(1)9 Key: QNMKKFHJKJJOMZ-UHFFFAOYAO
SMILES C1(=C(C(=C(C(=C1I)I)I)I)I)I
Properties
Chemical formula	C6I6
Molar mass	833.493 g·mol−1
Appearance	orange crystals[1]
Density	4.60 g/cm3
Melting point	430 °C (806 °F; 703 K)[1]
Solubility in water	insoluble
Structure[2]
Crystal structure	monoclinic
Space group	P21/c, No. 14
Lattice constant	a = 8.87 Å, b = 4.29 Å, c = 16.28 Å α = 90°, β = 93°, γ = 90°
Related compounds
Related compounds	Hexafluorobenzene Hexachlorobenzene Hexabromobenzene
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Preparation

The compound was first prepared by iodination of benzoic acid in the presence of hot fuming sulfuric acid.^[4] Another method of synthesis is the reaction between benzene with periodic acid and potassium iodide in sulfuric acid at 100 °C. This method instead produces 1,2,4,5-tetraiodobenzene if done at room temperature.^[5]

Properties

Physical properties

Hexaiodobenzene forms orange needles that are practically insoluble in water, but sparingly soluble in N-methyl-2-pyrrolidone and dimethyl sulfoxide. It melts at 430 °C, but also already begins to show some decomposition at 370 °C, forming I₂.^[1]

Crystallographic properties

The crystals are monoclinic and pseudohexagonal, with centrosymmetric C₆I₆ units. The carbon atoms lie in a plane with C–C distances about 141 pm, while the nearby iodine atoms show very small displacements (about 4 pm) above and below the ring. The shortest intermolecular distance, 376 pm, is notably short compared to twice the Van der Waals radius, which is 430 pm.^[2] The structure is retained at high pressures up to 9.7 GPa.^[6]