Rhenium versus cadmium: an alternative structure for a thermally stable cadmium carbonyl compound

An alternative description is provided for the previously reported novel tetranuclear cadmium carbonyl compound, [Cd(CO)₃(C₆H₃Cl)]₄. Specifically, consideration of single crystal X-ray diffraction data indicates that the compound is better formulated as the rhenium compound, [Re(CO)₃(C₄N₂H₃S)]₄. Furthermore, density functional theory calculations predict that, if it were to exist, [Cd(CO)₃(C₆H₃Cl)]₄ would have a very different structure to that reported. While it is well known that X-ray diffraction may not reliably distinguish between atoms of similar atomic number (e.g. N/C and Cl/S), it is not generally recognized that two atoms with very different atomic numbers could be misassigned. The misidentification of two elements as diverse as Re and Cd (ΔZ = 27) is unexpected and serves as an important caveat for structure determinations.