How to make grow a crystal-example of solvent diffusion

Practically all chemists knows the necessity of recrystallization as a method of purification of solid products . Less known, this method is useful for make growing crystals. The goal in growing crystals for X- Ray diffraction experiment is to grow sigle crystals. The optimum size for a crystal is about 0.2 to 0.4 mm in at least two directions of space. The factors during crystal growth which affect the size of the crystal are:

  1. The solubility of the compound in the solvent chosen for recrystallization
  2. Mechanical agitation to the system

Solvent: Choose a solvent in which your compound is moderately soluble. If the solute is too soluble, this will result in small crystal size. And supersaturated solutions tends to give crystals which are too small in size too.

Mechanics: Mechanical disturbance of the crystal growing results in smaller crystals. The crystals have to grow with a minimum of disturbance. So, don’t check how your crystals are growing every days!!! Set up the crystals growing attempt in a quiet, out of the way place for a week.

Experimental method for solvent diffusion

This method is good for mg amounts of materials which are sensitive to ambient laboratory conditions (air, moisture,..).

A compound C1 was dissolved in a solvent S1(this mixture is called M1) and placed in the diffusion tube. A mixture of the solvents which dissolved compound 1 and then the second compound was placed on the top of the first mixture M1.

The second compound C2 was dissolved in a solvent (this mixture is called M2) and placed in the top of pure solvents.

The diffusion tube is closed, then placed stand in a frizzer for several days.

The slow diffusion of M1 and M2 through pure solvent will cause crystals to form.



Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s