Synthesis, structural characterization of nickel(II) hexaazamacrotetracyclic complexes with azido, isocyanato and nitrito ligands

The reaction of [Ni(L)](ClO4)2·2H2O (L=1,3,10,12,16,19-hexaazatetracyclo[17,3,1,112.16,04.9]tetracosane) with NaN3, NaNCO and KNO2 yields mononuclear nickel(II) complexes, [Ni(L)(N3)2]·2H2O (1), [Ni(L)(NCO)2]·2H2O (2) and [Ni(L)(ONO)2]·2H2O (3). These complexes have been characterized by X-ray crystallography, electronic absorption and cyclic voltammetry. The crystal structures of the complexes show that all structures are centrosymmetric and the nickel centre has an axially elongated octahedral geometry with four nitrogen atoms of the macrocycle and two coordinated axial ligands. Electronic spectra of the complexes also exhibit a high-spin octahedral environment. Cyclic voltammetry of the complexes undergoes a irreversible one-electron wave corresponding to Ni(II)/Ni(I) processes. The electronic spectra and electrochemical behaviors of the complexes are significantly affected by the nature of the azido, isocyanato and nitrito ligands.