The Disproportionation of [Ni(tacn)]2+ in Ni2+ and [Ni(tacn)2]2+ Crystallographically Demonstrated (tacn=1,4,7-Triazacyclononane)

From an EtOH/H2O solution, 0.3M each of Ni2+ and cyclic triamine tacn (2; tacn=1,4,7-triazacyclononane), after 10 min refluxing and cooling at room temperature, copious and comparable amounts of blue crystals (containing the complex [Ni(tacn)(H2O)3]2+) and pink crystals (containing in the same cell both [Ni(H2O)6]2+ and [Ni(tacn)2]2+) precipitated. This unusual behaviour is ascribed to the fact that at the refluxing temperature the three species are present at the equilibrium in similar concentrations, which are frozen on cooling, due to the inertness of the macrocyclic complexes [Ni(tacn)(H2O)3]2+ and [Ni(tacn)2]2+.