A series of dichloroferrous complexes with ligands derived from the tris(2-pyridylmethyl)amine tripod has been prepared and characterized. The X-ray crystal structures of the complexes [bis(2-bromo-6-pyridylmethyl)(2-pyridylmethyl)amine]Fe(II)Cl(2) ((Br(2)TPA)Fe(II)Cl(2)) and [bis(2-phenyl-6-pyridylmethyl)(2-pyridylmethyl)amine]Fe(II)Cl(2), ((Ph(2)TPA)Fe(II)Cl(2)) are reported. In these complexes, the tripod coordinates in the tridentate mode, with a substituted pyridyl arm dangling away from the metal. Both complexes have a trigonal bipyramidal iron center with two equatorial chloride ions. Their crystal structures are compared with those of the [tris(2-pyridylmethyl)amine]Fe(II)Cl(2) and [(2-bromo-6-pyridylmethyl)bis(2-pyridylmethyl)amine]Fe(II)Cl(2) complexes ((TPA)Fe(II)Cl(2) and (BrTPA)Fe(II)Cl(2), respectively) in which the ligand coordinates in the tetradentate mode. For all complexes, the metal to ligand distances are systematically above the value of 2.0 A, and (1)H NMR displays paramagnetically shifted resonances with short relaxation times. This indicates that the iron is in a high-spin state. Electric conductivity measurements show that, for all complexes, the measured values lie within the same range, significantly below those expected for ionic complexes. Together with the analysis of the UV-visible and NMR data, this strongly suggests that the coordination mode of the tripod is retained in solution.

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The condensation of 5-chlorocarbonyl-2,2'-bipyridine with a variety of rigid aromatic diamines, L, gave a series of new bisamido-2,2'-bipyridine based ligands (L = 4,4'-methylenediamine, L1; L = 1,1-bis(4-aminophenyl)cyclohexane, L2; L = 1,1-bis(4-amino-3,5-dimethylphenyl)cyclohexane, L3) capable of forming dinuclear triple helicate complexes on coordination to Fe(II). The reaction of various Fe(II) salts with gave: {[Fe2(L1)3](BF4)4, 1; [Fe2(L1)3](ClO4)4, 2; [Fe2(L1)3]Cl4, 3; [Fe2(L1)3](SO4)2, 4; [Fe2(L2)3](BF4)4, 5; [Fe2(L2)3]Cl4, 6; [Fe2(L3)3](BF4)4; 7; [Fe2(L3)3]Cl4, 8; and [Fe2(L3)3](SO4)2, 9, as determined by UV-Vis, IR and 1H NMR spectroscopy, electrospray mass spectrometry (ESMS) and elemental analyses. A UV-Vis complexometric titration experiment between L3 and Fe(BF4)2 established conclusively a [Fe2(L3)3]4+ product species. 1H NMR spectroscopy showed that the complexes exist as both rac-(helical) and meso-(non-helical) isomers in DMSO-d6 solution at 298 K. L1-L3 were designed such that following complexation, six amide hydrogen atoms would line an inter-strand intrahelical cavity of sufficient size to facilitate the binding of guest species within it. Indeed, ESMS studies showed characteristic peaks typical of complex-anion species in solution. Furthermore, 1H NMR titration experiments showed that anions bind within the intrahelical cavity as titration of 1, 5 and 7 with Bu4NCl showed significant downfield shifts in the amide and bipyridyl H6 proton resonances to yield a species of 1 : 2 host to guest stoichiometry. Moreover, addition of Bu4NCl to 1, 5 and 7 shifted the rac-/meso-species distribution from 1 : 2 in favour of the meso- to 100% in favour of the rac-isomer, showing that Cl- ions favour the formation of the triple helicate species in DMSO-d6 solution.