The first seven-coordinated iron(II) complex with a nitrogen donor set hepta-dentate macrocyclic polyamine ligand and different coordination modes with its cobalt(II) analogue

The Fe2+ and Co2+ complexes with a hepta-dentate ligand, 1-methyl-4,7,10-tr is(2-pyridylmethyl)-1,4,7,10-tetraazacyclododecane (L), have been synthesiz ed and their crystal structures determined by X-ray diffraction analyses. T he two complexes have been found to have different coordination modes. The Fe2+ complex (I) is seven-coordinated with the four cyclen (cyclen = 1,4,7, 10-tetraazacyclododecane) nitrogen donors and all three pendant pyridine ni trogens, adopting a mono-capped distorted octahedral coordination geometry. To our knowledge, this is the first example of a structurally characterize d seven-coordinated Fe2+ complex formed with only one N-7 done; set ligand. Whereas the Co2+ complex (TI) of L is a normal six-coordination with four cyclen nitrogen donors and two pendant pyridines to give a distorted octahe dron in which one pendant pyridine nitrogen remains uncoordinated. (C) 2000 Elsevier Science B.V. All rights reserved.