Prepare your reaction mixture in an apparatus that is devoid of moisture and oxygen gas. Air- and moisture-sensitive compounds are typically prepared in an inert atmosphere dry box or a Schlenk line. Once your reaction is complete, it is ready for purification by crystallization. If you heated your reaction, let it cool to room temperature.
Dissolve your compound in a dry, degassed solvent. If you are following an established procedure, use the listed solvent to dissolve your iridium complex. If you are isolating a new compound, try to dissolve the compound using the least polar solvent available. Add a small amount of solvent and watch to see if it dissolves the compound. If the solvent does not dissolve the compound, remove the solvent under reduced pressure. Try more and more polar solvents until one of them dissolves your compound. Use this solvent to dissolve your compound. Most of the solids in your reaction mixture should be dissolved, with the exception of any simple salt byproducts like NaCl.
Dry and weigh your receiving flask. Choose a receiving flask that is more than twice the volume of the filtered solution.
Filter your product solution using dry box or Schlenk line techniques into your receiving flask.
Concentrate and cool your solution under reduced pressure. Hold the flask in your hand and swirl as you reduce pressure gently. Make slow changes and swirl the solution to avoid losing material by violent boiling. Continue to evaporate the solvent under reduced pressure until you observe solids precipitating out of the solution. Refill your flask with inert gas and allow it to return to room temperature.
Grow crystals at low temperature. Seal your flask and place it in a refrigerator, freezer or cold bath. The temperature must be higher than the melting point of the solvent so that it does not freeze. Check your reaction mixture after three hours, 12 hours and 24 hours for crystal growth.
Remove the remaining solution when crystal growth has stopped. Use dry box or Schlenk line techniques to remove the remaining solution, the "mother liquors," from the flask. The solid crystals will remain. Wash the crystals with an inert low-boiling solvent, like pentane or hexane, and remove the wash.
Dry your crystals under reduced pressure. This removes residual solvent.
Weigh your crystals to determine yield using a balance. You may weigh the crystals and the flask and subtract the mass of the flask. Alternatively, you can scrape the crystals out of the receiving flask and measure them over weighing paper in a dry box.
Recrystallize the remaining solution to increase yield. Your "mother liquors" may contain substantial product. Take care to repeat the crystallization process so that you produce purified product.