Iron(III) activation hits a [4+4] macrocycle

摘要

The tetranuclear complex [Fe~(III)_2(L')(OH)(CH_3O)]_2,1,has been synthesised from the reaction of either ferrous [in excess as 4 :1 or stoichiometric 2 :1 iron(II):H_4L] or ferric ions [4 :1 iron(III):H_4L] with the large macrocycle,H_4L,using aerobic conditions in methanol in the presence of triethylamine.The structure of 1 was determined by single-crystal X-ray diffraction.These reaction conditions lead to the modification of the original macrocycle through the incorporation of a methylene group between two amine groups to give an imidazolidine ring in (L')~(4-).The controlled addition of formaldehyde into the reaction system results in a significantly improved yield of 1,suggesting that it is involved in the reaction mechanism.The (L')~(4-) macrocycle binds to two,well-separated,iron(III) centres [Fe(l)...Fe(1a) > 8 A].Each iron(III) centre is further linked via hydroxy and methoxy bridges to equivalent iron(III) centres contained in a second macrocycle.Overall this gives a structure containing two {Fe(OH)(CH_3O)Fe} dimers [Fe(l) ...Fe(2) ca.3.2 A] sandwiched by two (L')~(4-) macrocycles.The complex was further characterised by SQUID magnetic measurements and can be interpreted in terms of two isolated antiferromagnetically coupled Fe(III) dimers (J=-23.75K).