Nitroxides radicals are attractive tools for study in biochemistry and materials science. A polymorphic crystal of a nitroxide radical, 4,4,5,5-tetramethyl-2-phenylimidazoline-1-oxyl 1-oxide was prepared and structurally characterised. The compound crystallised in the monoclinic, space group C2/c with a = 11.170(6) angstrom, b = 10.417(5) angstrom, c = 10.995(5) angstrom, beta = 108.059(9), V = 1216.3(10) angstrom, C13H17N2O2, M-r = 233.29, D-c= 1.274 g cm(-3), mu (MoK alpha) = 0.087 mm(-1), Z = 4 and F(000) = 500. The structure was solved by direct methods and refined by least-squares techniq...