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

摘要

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 [M _2L_3]~(4+) complexes; although with 4 and 6 there was also evidence for the (minor) formation of the corresponding [M _4L_6]~(8+) species. Overall, this result contrasts with the behaviour of the essentially rigid 'parent' quaterpyridine 1 for which only tetrahedral [M_4L_6]~(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 [M_2L_3]~(4+) and [M _4L_6]~(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 [H _2O?Ni_2(4)_3](PF_6) _4·THF·2.2H_2O, [Ni_2(6) _3](PF_6)_4·1.95MeCN·1. 2THF·1.8H_2O, and the very unusual triple helicate PF _6~- inclusion complex, [(PF_6)?Ni _2(5)_3](PF_6)_3·1. 75MeCN·5.25THF·0.25H_2O are reported.