preparing cis and trans K[Cr(C2O4)2(H2O)2), the question is: Suggest how the isomerization from trans to cis isomer might occured. How does this compare to the isomerism of trans-[Co(NH3)4Cl2]Cl?

Now would this ismerization happen because of physical properties, like the influences of the temperature and time of evaporation, because we took a week to do the trans evaporation and only a couple of hours for the cis configuration? or is it something else?