Synthesis and structures of two cobalt(III) complexes with N4 donor ligands: Isolation of a unique bis-hemiaminal ether ligand as the metal complex

Two cobalt(III) complexes, [CoL1(N3)2]ClO4·H2O (1) and [CoL2(N3)2]NO3 (2), where L1 = N,N′-bis-(2-pyridylmethyl)-1,2-ethanediamine, L2 = N,N′-bis-(1-methoxy-1-pyridin-2-yl-methyl)-ethane-1,2-diamine and both ligands are tetradentate N4 donors, have been prepared and characterized by elemental analysis, IR and UV–Vis spectroscopy, cyclic voltammetry and single crystal X-ray diffraction studies. Both compounds assume an asymmetric cis-octahedral (N2/N2) geometry. Complex 1 crystallizes in the orthorhombic space group Pbca with cell dimensions a = 9.7593(2) Å, b = 16.8640(3) Å, c = 25.8206(5) Å, Z = 8, whereas complex 2 crystallizes in the monoclinic space group P21/c with cell dimensions a = 14.437(3) Å, b = 15.596(3) Å, c = 19.187(3) Å, β = 93.642(2), Z = 8. In complex 2, a new bis-hemiaminal ether ligand was found to be “trapped”. Hemiaminal ethers are known to be very unstable intermediates and no crystal structure of any bis-hemiaminal ether has been reported to date. Complex 2 represents a uniquely stable system containing the trapped bis-hemiaminal ether L2.

Graphical abstractTwo cobalt(III) complexes, [CoL1(N3)2]ClO4·H2O (1) and [CoL2(N3)2]NO3 (2), where L1 = N,N′-bis-(2-pyridylmethyl)-1,2-ethanediamine, L2 = N,N′-bis-(1-methoxy-1-pyridin-2-yl-methyl)-ethane-1,2-diamine and both ligands are tetradentate N4 ligands, have been prepared and characterized by elemental analysis, IR and UV–Vis spectroscopy, cyclic voltammetry and single crystal X-ray diffraction studies. Both the complexes assume an asymmetric cis-octahedral (N2/N2) geometry. The chelating ligands were prepared in situ by simple condensation reactions or condensation followed by borohydride reduction. In complex 2, a new bis-hemiaminal ether ligand was found to be “trapped”. Hemiaminal ethers are known to be very unstable intermediates and no crystal structure of any bis-hemiaminal ether has been reported to date. Complex 2 represents a uniquely stable system containing the trapped bis-hemiaminal ether L2.Figure optionsDownload full-size imageDownload as PowerPoint slide