a compound made in the first part of an experiment,
[Co(NH3)5Cl]Cl2 appeared to be a dark brown/orange/purple color.
This product was then used as a reactant to synthesize [Co(NH3)5ONO], which was a red color.
how do you account for the differences in color between these two?
See
http://en.wikipedia.org/wiki/Jahn-Teller_effect
The differences in color between the compounds [Co(NH3)5Cl]Cl2 and [Co(NH3)5ONO] can be explained by considering the chemical changes that occur during the synthesis reaction.
1. Starting compound [Co(NH3)5Cl]Cl2:
The compound [Co(NH3)5Cl]Cl2 initially appears as a dark brown/orange/purple color. This color is likely due to the presence of a cobalt (Co) ion complexed with five ammonia (NH3) ligands and one chloride (Cl-) ligand. The color arises from the absorption of certain wavelengths of light which are not transmitted, leading to the observed color.
2. Synthesized compound [Co(NH3)5ONO]:
During the synthesis reaction, [Co(NH3)5Cl]Cl2 reacts with a reactant containing the nitrite ion (NO2-) to form [Co(NH3)5ONO]. The change in color from dark brown/orange/purple to red can be attributed to the different ligands (Cl- and ONO-) complexed with the central cobalt ion.
In general, transition metal complexes can exhibit different colors due to the phenomenon called "ligand field theory." The color change is influenced by the properties of the ligands coordinating with the metal ion and the resulting electronic transitions that occur within the complex. Different ligands can cause different energy gaps between the d-orbitals of the metal ion, leading to the absorption of different wavelengths of light and, therefore, different colors being observed.
Therefore, the change in ligands from chloride (Cl-) to nitroso (ONO-) in the synthesis reaction leads to a change in the electronic structure of the complex, resulting in a different color being observed.