Rhenium(IV) chloride

Template:Chembox Rhenium(IV) chloride is the inorganic compound with the formula ReCl₄. This black solid is of interest as a binary phase but otherwise is of little practical value. A second polymorph of ReCl₄ is also known.

Preparation

ReCl₄ can be prepared by comproportionation of rhenium(V) chloride and rhenium(III) chloride. It can also be produced by reduction of rhenium(V) chloride with antimony trichloride.

$\mathrm{2}\mathrm{R}\mathrm{e}\mathrm{C}{\mathrm{l}}_{\mathrm{5}}\mathrm{+}\mathrm{S}\mathrm{b}\mathrm{C}{\mathrm{l}}_{\mathrm{3}}\mathrm{⟶}\mathrm{2}\mathrm{R}\mathrm{e}\mathrm{C}{\mathrm{l}}_{\mathrm{4}}\mathrm{+}\mathrm{S}\mathrm{b}\mathrm{C}{\mathrm{l}}_{\mathrm{5}}$

Tetrachloroethylene at 120 °C is also effective as a reductant:

$\mathrm{2}\mathrm{R}\mathrm{e}\mathrm{C}{\mathrm{l}}_{\mathrm{5}}\mathrm{+}{\mathrm{C}}_{\mathrm{2}}\mathrm{C}{\mathrm{l}}_{\mathrm{4}}\mathrm{⟶}\mathrm{2}\mathrm{R}\mathrm{e}\mathrm{C}{\mathrm{l}}_{\mathrm{4}}\mathrm{+}{\mathrm{C}}_{\mathrm{2}}\mathrm{C}{\mathrm{l}}_{\mathrm{6}}$

Structure

X-ray crystallography reveals a polymeric structure. The Re–Re bonding distance is 2.728 Å. Re centers are octahedral, being surrounded by six chloride ligands. Pairs of octahedra share faces. The Re₂Cl₉ subunits are linked by bridging chloride ligands. The structural motif - corner-shared bioctahedra - is unusual in the binary metal halides.