Among [Co(CN)6]³, [Co(NH3)6]³+, and [CoF6]³, which is expected to be colorless?

The expected colorlessness of [CoF6]³ can be attributed to its electronic structure and the nature of its ligands. Cobalt in these complexes is typically in the +3 oxidation state. The crystal field theory helps explain the behavior of these complexes based on the splitting of d-orbitals in the presence of ligands.

In this case, the ligand fluoride (F⁻) is a weak field ligand, which results in relatively low splitting of the d-orbitals compared to stronger field ligands like cyanide (CN⁻) and ammonia (NH₃). The energy required to promote an electron from a lower energy d-orbital to a higher one in the presence of fluoride is higher than the energy of the light in the visible spectrum. As a result, there are no electronic transitions in the visible range, which leads to the complex being colorless.

In contrast, [Co(CN)6]³, with strong field CN⁻ ligands, experiences significant crystal field splitting, leading to transitions within the visible spectrum and producing color. Similarly, [Co(NH3)6]³+ will also have visible transitions due to the intermediate field strength of NH₃ as a ligand, resulting in color