X-ray powder diffraction data for two ionic salts containing imidazole (Him) complexes of the magnesium(II) ion, [Mg(Him)4(H2O)2]Cl2 and [Mg(Him)6](NO3)2, are reported. Their crystal and molecular structures were determined by simulated annealing and full-profile Rietveld refinement methods. [Mg(Him)4(H2O)2]Cl2 was found to crystallize in the monoclinic system with space group C2/c, a=12.3980(3) Å, b=11.0234(2) Å, c=14.4691(3) Å, and β=107.024(1)°. [Mg(Him)6](NO3)2 crystallizes in the trigonal R-3 space group with a=b=12.4631(4) Å and c=14.9449(6)
Å. Both species contain centrosymmetric complexes, and Mg is octahedrally coordinated by six imidazoles, as in [Mg(Him)6](NO3)2, or by four imidazoles and two water molecules, as in [Mg(Him)4(H2O)2]Cl2. Additional analytic, thermogravimetric, calorimetric, and spectroscopic characterizations were also performed.