Although hydrated rhodium trichloride is widely marketed and often used, the structure of this red solid has not been elucidated crystallographically.

The relative distribution of these species determines the colour of the solutions, which can range from yellow (the hexaaquo ion) to "raspberry-red".

These reactions are facilitated by the fact that hydrated rhodium trichloride is soluble in a range of polar organic solvents.

Evidence for the affinity of rhodium chlorides for oxygen-based ligands is provided by the chloro-aquo complexes discussed above.

Aqueous solutions of rhodium trichloride react with ammonia to give the salt pentamminerhodium chloride, [RhCl(NH3)5]Cl2.

[10] Rhodium(III) also forms a range of complexes with soft Lewis bases, such as thioethers, phosphines, and arsines.

[3] Reaction of RhCl3(H2O)3 under mild conditions with tertiary phosphines affords adducts akin to the aforementioned thioether complexes.

When these reactions are conducted in boiling ethanol solution, reduction occurs, leading to rhodium(I) derivatives.

Either the ethanol solvent or the phosphine serves as reductant:[12][13] Unlike most other air-stable metal salts, hydrated rhodium trichloride reacts under mild conditions (near room temperature, one atmosphere) with carbon monoxide and many olefins.

[14] When hydrated rhodium trichloride is treated with cyclopentadienes, organometallic half sandwich compounds can be produced.

Further carbonylation in the presence of sodium citrate as a reductant leads to tetrarhodium dodecacarbonyl, Rh4(CO)12, a rhodium(0) cluster compound.

This and many related discoveries nurtured the then young field of homogeneous catalysis, wherein the catalysts are dissolved in the medium with the substrate.

Catalysis by rhodium is so efficient that it has significantly displaced the previous technology based on less expensive cobalt catalysts.