Please kindly help me with the appropriate solvent that can be used to obtained pure crystals on Iron and chromium complexes with cyanide, thiocyanide and EDTA.
This is very correct, Growing crystals suitable for X-ray crystallography is more of an art, You need to try a number of different solvents and mixtures of solvents, depending on the solubility of your complexes. You need to also try different crystal growth methods. Vapour diffusion tends to grow better quality crystals in my experience. You just have to find what is best for your class of compounds by trial and error.