if slow evaporation fails, you can try other methods like diffusing other solvents, layering method, vapor diffusion etc

Have you tried using a seeding surface of some type.. This could be a glass stirring rod with an inscribed scratch to serve as a crystallization initiation  site.

We had success by performing the synthesis at much lower Ts (in the freezer!) in a spotless clean rxn vessel.

Choice of the solvent or solvent mixtures-substance should not be highly soluble nor insoluble-and slow evaporation, without disturbing it physically and without temperature fluctuation is advisable.   Seeding may also help.

You need to change the solvent, I think it may be helpful... also, evaporation in room temperature also useful step.

According to your information the complex is highly soluble in DCM, if so you can make a high concentrated DCM sample of the complex and add a layer of pure hexane extremely carefully without disturbing the DCM layer on top of it (usually double the amount of DCM) Then leave it in the refrigerator without any disturbances.

Try this it should work! 

Evaporation very slowly in partially closed system may be useful