Nickel(II) and iron(II) triple helicates assembled from expanded quaterpyridines incorporating flexible linkages.

In the present study the interaction of Fe(II) and Ni(II) with the related expanded quaterpyridines, 1,2-, 1,3- and 1,4-bis-(5'-methyl-[2,2']bipyridinyl-5-ylmethoxy)benzene ligands (4-6 respectively), incorporating flexible, bis-aryl/methylene ether linkages in the bridges between the dipyridyl domains, was shown to predominantly result in the assembly of [M2L3](4+) complexes; although with 4 and 6 there was also evidence for the (minor) formation of the corresponding [M4L6](8+) species. Overall, this result contrasts with the behaviour of the essentially rigid `parent' quaterpyridine 1 for which only tetrahedral [M4L6](8+) cage species were observed when reacted with various Fe(II) salts. It also contrasts with that observed for 2 and 3 incorporating essentially rigid substituted phenylene and biphenylene bridges between the dipyridyl domains where reaction with Fe(II) and Ni(II) yielded both [M2L3](4+) and [M4L6](8+) complex types, but in this case it was the latter species that was assigned as the thermodynamically favoured product type. The X-ray structures of the triple helicate complexes [H2O subset of Ni-2(4)(3)](PF6)(4)center dot THF center dot 2.2H(2)O, [Ni-2(6)(3)](PF6)(4)center dot 1.95MeCN center dot 1.2THF center dot 1.8H(2)O, and the very unusual triple helicate PF6- inclusion complex, [(PF6)subset of Ni-2(5)(3)](PF6)(3)center dot 1.75MeCN center dot 5.25THF center dot 0.25H(2)O are reported.