Dear colleagues,
I am currently attempting to grow single crystals for SCXRD, but I am facing challenges due to the high solubility of my compound. The only solvents in which my sample dissolves well are DMF and DMSO. I tried the vapor diffusion method by dissolving approximately 5–7 mg of the sample in a small volume of DMF (0.2 mL) and using ethyl ether as the anti-solvent. However, I suspect that due to the compound’s high solubility in DMF, crystallization is hindered—it may be difficult for the solid to leave the primary solvent and nucleate at the interface during the diffusion process.
I came across some studies that successfully used ethanol as the anti-solvent for a similar compound, but given the solubility issue in DMF, I am wondering if there are specific strategies to facilitate crystal formation.
I would greatly appreciate any tips, alternative approaches, or tricks that might help optimize the crystallization process.
Thank you in advance for your insights!
If your compound only dissolves in polar solvents, I would recommend trying hot polar solvents such as methanol, acetonitrile or water. useful information about crystallization you can find here: www.unifr.ch/chem/en/assets/public/PDFWordDocuments/Guide%20for%20crystallization.pdf
Please note the convection method on page 10-11. I think it can be very useful in your case when crystallizing in a polar solvent where the solubility is quite low compared to DMF/DMSO, e.g. methanol or acetonitrile.
Check also hydrothermal synthesis crystallization - Water is a good solvent at 130-150-180C and appropriate pressure (protect yourself, there is a risk of explosion due to high pressure in the vessel and burns from steam.) However, a small volume vessel, such as a small glass tube ampoule with a diameter of 5-7 mm, is a good choice, also use a protective metal cylinder around it.
Dear Colleagues,
Thank you for your helpful suggestions!
Dr. Eduard Rusanov,
I have been trying to find more information on the recrystallization by convection method but have had difficulty locating detailed guidance. I was wondering if you could provide any advice on the appropriate sample and solvent volumes for this technique.
I came across a resource from MIT discussing Chuck Barnes’ adaptation of David Watkin’s construction (Watkin, D. J., J. Appl. Cryst. (1972), 5, 250) [https://chemistry.mit.edu/facilities-and-centers/x-ray-diffraction-facility/growing-quality-crystals/]. It suggests using a pipette, which I have been flame-sealing, and I noticed that it holds approximately 2–3 mL of liquid. Based on this, I was curious about the ideal sample quantity for this method or if you had any alternative recommendations.
I would greatly appreciate any insights you could share.
Best regards,
PR
No one knows better than you whether your compound dissolves better in a certain solvent, so try different methods, different amounts.
Also for diffusion methods, which usually work well, I would recommend using DMSO in combination with a miscible solvent such as diethyl ether/THF as an antisolvent. It is best to use long vessels such as an NMR tube for long diffusion times. Place the compound solution in DMSO (high density) as the bottom layer, then carefully and very slowly pipette the antisolvent into the top layer as a light antisolvent. Cap it and leave it in a quiet place, away from direct sunlight. Do not shake it. Depending on the diameter to length ratio of the vessel, the glass ampoule, the amount of the component, the concentration of the compound and its solubility, crystal growth is expected within a few hours or sometimes a few days.
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