Trirhenium nonachloride

Trirhenium nonachloride is a compound with the formula ReCl₃, sometimes also written Re₃Cl₉. It is a dark red hygroscopic solid that is insoluble in ordinary solvents. The compound is important in the history of inorganic chemistry as an early example of a cluster compound with metal-metal bonds.^[1] It is used as a starting material for synthesis of other rhenium complexes.

Trirhenium nonachloride

Names
IUPAC name Rhenium(III) chloride
Other names Rhenium trichloride
Identifiers
CAS Number	13569-63-6 Y
3D model (JSmol)	ReCl3: Interactive image Re3Cl9: Interactive image
ECHA InfoCard	100.033.610
EC Number	236-987-1
PubChem CID	83581
CompTox Dashboard (EPA)	DTXSID8065537
InChI InChI=1S/3ClH.Re/h3*1H;/q;;;+3/p-3
SMILES ReCl3: Cl[Re](Cl)Cl Re3Cl9: Cl[Re-]12(Cl)([Cl+]3)[Re-]3(Cl)(Cl)([Cl+]4)[Re-]14(Cl)(Cl)([Cl+]2)
Properties
Chemical formula	ReCl3
Molar mass	292.57 g/mol
Appearance	red, crystalline, nonvolatile solid
Density	4800 kg/m3
Melting point	N/A
Boiling point	500 °C (932 °F; 773 K) (decomposes)
Solubility in water	hydrolyzes to form Re2O3.xH2O.
Structure
Crystal structure	Rhombohedral, hR72
Space group	R-3m, No. 166
Molecular shape	(trimeric solid and in solution) (dimeric in acetic acid)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Corrosive (C)
Safety data sheet (SDS)	External MSDS
Related compounds
Other anions	Rhenium tribromide Rhenium triiodide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Structure and physical properties

As shown by X-ray crystallography trirhenium nonachloride consists of Re₃Cl₁₂ subunits that share three chloride bridges with adjacent clusters. The interconnected network of clusters forms sheets. Around each Re center are seven ligands, four bridging chlorides, one terminal chloride, and two Re-Re bonds.^[2]

Re₃Cl₁₂ cluster within ReCl₃, shown with full coordination sphere around each chloride.

The hydrate is molecular with the formula Re₃Cl₉(H₂O)₃.^[3]

The heat of oxidation is evaluated according to the equation:

1/3 Re₃Cl₉ + 4 OH⁻ + 2 OCl⁻ → ReO₄⁻ + 2 H₂O + 5Cl⁻

The enthalpy for this process is 190.7 ± 0.2 kcal/mol.^[2]

Preparation and reactions

The compound was discovered in 1932.^[4] Trirhenium nonachloride is efficiently prepared by thermal decomposition of rhenium pentachloride or hexachlororhenic(IV) acid:^[5]

3 ReCl₅ → Re₃Cl₉ + 3 Cl₂

If the sample is vacuum sublimed at 500 °C, the resulting material is comparatively unreactive. The partially hydrated material such as Re₃Cl₉(H₂O)₄^[6] can be more useful synthetically. Other synthetic methods include treating rhenium with sulfuryl chloride. This process is sometimes conducted with the addition of aluminium chloride.^[2] It is also obtained by heating Re₂(O₂CCH₃)₄Cl₂ under HCl:

3/2 Re₂(O₂CCH₃)₄Cl₂ + 6 HCl → Re₃Cl₉ + 6 HO₂CCH₃

Reaction of the tri- and pentachlorides gives rhenium tetrachloride:

3 ReCl₅ + Re₃Cl₉ → 6 ReCl₄