Tetrahydropoxen: 2,2 '-(1,2-ethanediylbis(iminomethylene))bis(pyridine N-oxide) and its complexes. X-ray structure of [Cu(H-4-poxen)H2O](ClO4)center dot H2O and [Co(poxen)H2O](ClO4)(2)

The condensation reaction of 2-pyridinecarboxaldehyde N-oxide with ethylene diamine yields the tetradentate ligand L-1 = poxen. Hydrogenation then prod uces tetrahydropoxen, L-2 = H-4-poxen, which has been isolated in a free fo rm. Several metal complexes of the formula [M(H-4-poxen)](ClO4)(2) . nH(2)O have been prepared (M=Mn, Cu and Zn) and investigated. The X-ray structure of [Cu(H-4-poxen)H2O] (ClO4)(2) . H2O shows that the copper atom is pentac oordinate, the poxen ligand forming a base of the tetragonal pyramid; the a qua ligand is situated in the apical position inside the cavity formed by t he ligand arms. In contrast, in the case of [Co(poxen)H2O] (ClO4)(2), the a pical aqua ligand is situated outside the 'cavity' formed by the dehydrogen ated ligand arms. (C) 2000 Elsevier Science Ltd All rights reserved.