Syntheses, structural studies and solution properties of iron complexes ofsome amide-substituted calixarenes

Iron(III) complexes of 5,11,17,23-tetra-tert-butyl-24-hydroxy-26,27,28-tris (diethylcarbamoylmethoxy) calix[4] arene (II) and 5,11,17,23,29,35-hexa-ter t-butyl-36,39-dihydroxy-37,38,40,41-tetrakis(diethylcarbamoylmethoxy) calix [6] arene (IV) have been synthesised, and a single crystal structure determ ination has been carried out on [Fe(II - H)] (FeCl4)(2); the iron in the co mplex cation is bound to all seven O atoms of the calixarene with the short est Fe-O distance to the phenolate O atom. The voltammetric properties of t hese complexes and the previously described Fe(III) complex of 5,11,17,23-t etra-tert-butyl-25,27-dihydroxy-26,28-bis(diethylcarbamoylmethoxy) calix[4] arene (I) have been studied. The results suggest that the complexes of I a nd II undergo a reduction which is metal-centred, and an oxidation which is ligand-centred.