Metallacrowns form via self-assembly, i.e. by dissolving the ligand in a solvent followed by the desired metal salt. 
The first reported metallacrown was Mn(OAc)(DMF)[12-MC-4]. Metallacrowns can be prepared with a variety of metals in the ring and in a variety of ring sizes. Many metallacrowns have been prepared, including 9-MC-3, 15-MC-5, and 18-MC-6.  Ring size is controlled by a number of factors, such as the geometry of the ligand chelate ring, ring metal Jahn–Teller distortion, central metal size, steric effects, and stoichiometry.  Common ring metals have included V(III), Mn(III), Fe(III), Ni(II) and Cu(II). Hydroxamic acids, such as salicylhydroxamic acid, and oximes are commonly utilized in metallacrown ligands.