The syntheses of the novel hexadentate nitrogen ligand 1,10-bis(2-pyridylmethyl)-1,4,7,10-tetraazadecane (bpteta), C18H28N6, and of its complexes with iron(II), manganese(II), and nickel(II)are reported. The structures of the mononuclear complexes [M(bpteta)](ClO4)2 (M = Fe, Mn, Ni) and that of the tetranuclear iron(III) complex {[Fe2(mu-O)(mu-OAC)2]2(mu-bpteta)2}(ClO4)4 have been determined by three-dimensional X-ray diffraction methods. The iron(II) complex [Fe(bpteta)](ClO4)2 (1) crystallizes in the space group P2(1)/c of the monoclinic system with four molecules in a cell of dimensions a = 12.4%(2) angstrom, b = 12.148(2) angstrom, c = 16.800(3) angstrom, and beta = 109.12(3)degrees. The nickel(II) complex [Ni(bpteta)](ClO4)2 (3) is isomorphous with the iron analogue, with cell dimensions a = 12.507(3) angstrom, b = 12.307(2) angstrom, c = 16.777(3) angstrom, and beta = 108.80(3)degrees. The geometry at iron or nickel is six-coordinate pseudooctahedral, with pyridine nitrogen atoms mutually cis and trans to amine nitrogen atoms. The manganese(II) complex [Mn(bpteta)](ClO4)2 (2) also crystallizes in the space group P2(1)/c of the monoclinic system with four molecules in a cell of dimensions a = 13.869(3) angstrom, b = 8.710(2) angstrom, c = 20.710(4) angstrom, and beta = 91.07(2)degrees. The geometry at manganese is trigonal prismatic. The tetranuclear iron(III) complex {[Fe2(mu-O)(mu-OAc)2](mu-bpteta)2}-(ClO4)4 (4) crystallizes in the space group C2/c of the monoclinic system with four tetranuclear units in a cell of dimensions a = 23.414(5) angstrom, b = 22.669(5) angstrom, c = 14.017(3) angstrom, and beta = 105.77(2)degrees. The complex is best described as a dimer of dimers, in which two [N3Fe(mu-O)(mu-OAc)2FeN3] cores are spanned by the bpteta ligands. The geometry at each iron center is roughly octahedral, with facial coordination of three nitrogen atoms from the bpteta ligands and three bridging oxygen atoms from the one u-oxo and two mu-acetato groups. The Fe...Fe separation between the cores is 7.358 angstrom. The tetranuclear complex exhibits strong antiferromagnetic coupling with an exchange constant J = -120 cm-1, a values similar to those for related complexes and close to that for methemerythrin. The three monomeric complexes 1-3 exhibit quasi-reversible redox couples at +0.750, +1.100, and +1.455 V (vs Ag/AgCl in acetonitrile), respectively, corresponding to the Fe(II) <-> Fe(III), Mn(II) <-> Mn(III), and Ni(II) <-> Ni(III) processes. The tetranuclear complex 4 exhibits a single irreversible cathodic wave at -0.62 V, which is similar to the behavior of other known [Fe2(mu-O)(mu-OAc)2]2+ complexes.