A second crystal form of [Ni(2,2′-bipyridine)(H2O)3(NO3)](NO3) featuring a different molecular orientation

The molecular structure of a second form of [Ni(2,2′-bipyridine)(H2O)3(NO3)](NO3) is reported. The previous report is for a blue monoclinic polymorph. The second form is orthorhombic and crystallises as green blocks with unit cell parameters a = 9.1201(12) Å, b = 14.444(2) Å, c = 21.805(4) Å, V = 2872.4(8) Å3, Z = 8. The complex was characterised by elemental analysis, infrared spectroscopy, UV–Vis spectroscopy, and thermogravimetry. The bipyridine acts as a bidentate ligand to Ni2+ and the octahedral coordination is completed by three water molecules and one monodentate nitrate ion. A second nitrate forms hydrogen bonds to the bound water molecules. The difference between the two forms in terms of the molecular geometry is described in relation to other similar compounds. The key difference between the two forms is the orientation of the two nitrate anions, and hence the hydrogen bonding present.

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► A green form of this complex has been discovered in addition to the known blue form.
► Connectivity of the green and blue forms is identical.
► Orientation of nitrate groups is the principal difference between forms.
► Change in colour is associated with only a small change in metal coordination.