I have two ionic crystals (metal complexes). Both of them contain the same cation but the anion are different in one functional group. One is a CH3 and the other is a Cl. Both of the crystals have similar unit cell and space group. However, to obtain the same quality, one crystalise in 2 hrs and the other between 1 and 2 days. why? Think that it has to be with the thermodynamics of crystalllisation but I'm not sure how. What do you think?