[Exploring]

I'm preparing  Co, Cu, Zn and Ni complexes with the same ligand. I found that all complexes are isostructural (or almost), and very crystalline (by XRD). However, the complexes I prepare with nickel are amorphous (xrd) no matter the solvent used to precipitate the complex. This happens to me with many ligands, and I don't understand why nickel behaves so differently giving rise to complexes with such low crystallinity when Co, Cu or Zn counterparts produce very nice crystals using the same ligand(s). Any suggestion?. thanks for your help