Synthesis and properties of cobalt(III) complexes of 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,01.18,07.12]docosane

The octahedral cobalt(III) complexes, [Co(L)(int)2]Cl · 3H2O (1), [Co(L)(NCS)2]NCS · H2O (2) and [Co(L)(NCO)2]NCO · H2O (3) (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,01.18,07.12]docosane, int = isonicotinate) were obtained by the reactions of [Co(L)Cl2]Cl · 4H2O with the corresponding ligands. The X-ray analysis of 1 shows that the complex has an octahedral geometry formed by coordination of four secondary amines of the macrocycle and two oxygen atoms of the axial isonicotinate ligands. Complex 2 also has an octahedral geometry with four secondary amines of the macrocycle and two nitrogen atoms of the axial thiocyanate ligands. Electronic spectra of the complexes also exhibit a low-spin octahedral geometry. Cyclic voltammetry of the complexes undergoes a one-electron wave corresponding to a CoIII/CoII process. The electronic spectra and electrochemical behaviors of the complexes are significantly affected by the nature of the axial ligands.

Graphical abstractThe cobalt(III) complexes [Co(L)(int)2]Cl · 3H2O (1), [Co(L)(NCS)2]NCS · H2O (2) and [Co(L)(NCO)2]NCO · H2O (3) have been synthesized and structurally characterized. The crystal structures of 1 and 2 show that the cobalt centers have an octahedral geometry with four secondary amines of the macrocycle and two axial ligands.Figure optionsDownload full-size imageDownload as PowerPoint slide