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(N-3)(2)]ClO4 center dot H2O (1) and [CoL2(N-3)(2)]NO3 (2), where L-1 = N,N'-bis-(2-pyridylmethyl)-1,2-ethanediamine, L-2 = N,N'-bis-(1-methoxy-1-pyridin-2-yl-methyl)-ethane-1,2-diamine and both ligands are tetradentate N-4 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) angstrom, b = 16.8640(3) angstrom, c = 25.8206(5) degrees, Z = 8, whereas complex 2 crystallizes in the monoclinic space group P2(1)/c with cell dimensions a = 14.437(3) angstrom, b = 15.596(3)angstrom, c = 19.187(3) angstrom, beta = 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 L-2. (C) 2012 Elsevier Ltd. All rights reserved.