X-ray crystallography shows that the two Rh(I) centers are square planar with the dihedral angle of 126.8° between the two RhCl2 planes.

[1] First prepared by Walter Hieber,[2] it is typically prepared by treating hydrated rhodium trichloride with flowing carbon monoxide, according to this idealized redox equation: The complex reacts with triphenylphosphine to give the bis(triphenylphosphine)rhodium carbonyl chloride: With chloride salts, the dichloride anion forms: With acetylacetone, rhodium carbonyl chloride reacts to give dicarbonyl(acetylacetonato)rhodium(I).

The dimer reacts with a variety of Lewis bases (:B) to form adducts RhCl(CO)2:B.

The dissociation energy for rhodium(I) dicarbonyl chloride dimer, which is an energy contribution prior to reaction with the donor, has been determined by the ECW model to be 87.1 kJ mol−1 N-heterocyclic carbene (NHC) ligands react with rhodium carbonyl chloride to give monomeric cis-[RhCl(NHC)(CO)2] complexes.

The IR spectra of these complexes have been used to estimate the donor strength of NHCs.