The structure of the title compound has been established by single-crystal X-ray analysis. Crystals are orthorhombic, space group Pna2₁, a= 13.85(1), b= 9.83(1), c= 13.39(1)Å, Z= 4. The structure was solved by the heavy-atom method and atomic paramters were refined by full-matrix least-squares calculations tyo R 0.043 for 1 394 stattistically significant reflections from diffractometer measurements. The copper atom has a tetragonally distorted octahedral co-ordination in which four imidazole nitrogen atoms define the basal plane, mean Cu–N 2.011 Å, and unidentatate nitrato-oxygen atoms occupy the axial sites, mean Cu–O 2.566 Å. The mean copper atom displacement from the nitrato-group planes is 0.80Å. The imidazole N–H groups all participate in an extensive N–H ⋯ O hydrogen bonded network involving one the nitrato-oxgen atoms. The single-crystal e.s.r. and polarised electronic spectra are also reported and the electronic structure of the chromophore discussed with reference to these and the crystallographic data.