Hello,

The key is to saturate your solution and then change the conditions to make a super saturated solution and let it crystallize slowly. You can try slow evaporation of a small amount of the solution in a hood. It will take several days or weeks, so you will need to ensure that your compound is stable for that long in solution. You can also try vapor diffusion of a water-miscible solvent (one that your compound isn't soluble in), such as methanol.

Is your compound ionic? If it has the complex as an anion, try adding Ph4PCl (tetraphenylphoshonium chloride). If it has the complex as cation, try adding NaBPh4 (sodium tetraphenylborate). The BPh4 anion might be stable to those conditions though. You'd have to check.

Try a few different things and see. Good luck!

-Kyle

Hi,

You can crystallize out the complex through saturation of the solution as well as reducing the dielectric constant of the medium/solution. You can do this via adding some organic solvent that is missible but doesn't react with your cmplex.

Rozina

Hi,

adding an organic solvent rendering your complex less soluble is fine, you need to make sure it doesn't react with the HCl though, as it's obviously quite aggressive. Something like MeOH, EtOH should be good. You could try slowly diffusing these solvents into your HCl-solution: Take a beaker with your complex solution and put it into a bigger one containing the MeOH for example. Close the set up with a lid. 

You can also play around with the temperature, for instance by putting these setup or only a closed beaker with your solution into a fridge.

Good luck!

Hi,

VK's suggestion is good enough! You must have to be careful regarding acidic solutions and their concentrations during synthesis. The solvent you choose, can react with HCl as well. Alcohols are usually fine/okay, but with alcohols such as methanol or ethanol, we encounter another problem. These alcohols usually get oxidized by the complexes with high electrode potential such as ferric/ceric complexes with E < 1.00 V may oxidize the solvent. You should be careful to check if your complex is, in such an oxidation state that can not oxidize the alcohol, then you try, ferrous/cerous complexes can not oxidize alcohols, for example. If your complex is in reduced form which can not further be reduced by such a solvent, then you surely can try these solvents. Keep checking with small portions, to keep safe your mother solution! When trial becomes fruitful, then try it over excess! Temperture also helps!

Hope this helps!

Good luck!

The question is relatively imprecise - is the HCl necessary or just there as a byproduct?

If the former - then it's the wrong question - the right question is how to crystallize from 12N HCl because that is constant boiling and can be evaporated.

If the latter - then get rid of the HCl e.g. by liquid-liquid extraction or precipitation.

My general take is it's the wrong question. First step is to ISOLATE the complex - ideally in the absence of HCl. Trying to crystallize from the reaction mixture only works about 1 in 10 times or LESS - because synthesis is dirty and recrystallization is clean. The other 9 out of ten times, the CRUDE complex needs to be isolated first and then recrystallization conditions designed to purify it from there.

The rule of thumb is

i have synthesized complex in 6N HCl and need to isolate it from reaction mixture and purify it. The complex is water sensitive and soluble in methanol.

Well it can't be water sensitive - because 6 N HCl is about 48 M in water. BUT it could be that it requires HCl to stabilize the complex - if so then the complex must depend on H+ or Cl-, not knowing the complex I can only guess that it is likely to be a chloro complex - which is a pretty weak ligand (H+ is a pretty terrible ligand, while water is not half bad). So....to ISOLATE the complex...and get it way from the HCl, then it will be necessary to add CHLORIDE.  If that's right so far - then the classic approach would be to add a concentrated solution of Bu4NCl or PPh4Cl as the right way to go.

If you want to go old school then add liquid ZnCl2 (it's actually ZnCl2 - hydrate) and make the Zn salt. Zn is nice because it's redox inactive and pretty green. Same argument apply for things like CaCl2 etc. The complex can't be neutral - or it would crash out of water/HCl. So it's either a cation or anion. Assuming that you are asking for help for a real reason - then chances are it's a dication or dianion - because if it was a mono-cation or mono-anion you'd already have succesfully isolated it by adding Bu4NCl or NH4Ph4B or the like.

Try working with a dication or dianion - and salt it out by adding a higher alcohol like isopropanol.  The freezing point of HCl solutions are pretty low - so the refrigerator is clearly your friend here - especially if you can make it hot and concetrated to begin with (likely if it's a synthesis). For dianions it's tougher - sulfate, nitrate, chloride not always crystalline. I'm anti-perchlorate on safety grounds - kind of a risk reward thing - but there are a few other non-coordinating ions out there. If you want to go old school use an anionic complex as the counterion - it's an old trick but a good one - almost always a way to get a handle on solubility. It's dead weight - but sometimes you just want to get the complex isolated - and that's a way to do it e.g. CuCl4 or the like.

From what you've described - all roads lead to chloro complexes in one form or another.

If you want an example - try CuCl2 or CoCl2 in water and add conc HCl until it turns color - voila - a weakly bound chloro complex - sounds like what you are describing. - Werner chemistry.