Pentanuclear complexes with unusual structural topologies from the initial use of two aliphatic amino-alcohol ligands in Fe chemistry

Abstract

Five novel pentanuclear Fe 3+ clusters with the aliphatic amino-alcohol ligands 3-amino-1-propanol (Hap) and 2-(hydroxymethyl)piperidine (Hhmpip) [Fe 5(μ 3-Ο) 2(L) 4(O 2CR) 7] [L = ap -, R = Ph (1)

L = ap -, R = C(CH 3) 3 (2)

L = hmpip -, R = Ph (3)

L = hmpip -, R = C(CH 3) 3 (4)] and [Fe 5(μ 4-Ο)(μ 3-Ο)(O 2CC(CH 3) 3) 8(ap) 2Cl(HO 2CC(CH 3) 3)] (5) are reported. Compounds 1-4 were prepared from reactions of preformed trinuclear Fe 3+ clusters with the ligands in a molar ratio 1:5 in MeCN (1, 3, 4) or DMF (2), whereas compound 5 was prepared from the reaction of FeCl 3 with Hap in the presence of HO 2CC(CH 3) 3 in a molar ratio 1:3:2 in MeCN. To the best of our knowledge, 1-5 are the first examples of Fe 3+ complexes with the ligands Hap and Hhmpip. The structures of 1-4 are composed of a quasi-planar [Fe 5(μ 3-O) 2] 11+ core which consists of two vertex-sharing [Fe 3(μ 3-O)] 7+ triangles. The structure of 5 is based on the [Fe 5(μ 4- O)(μ 3-O)] 11+ core, in which the five Fe 3+ ions adopt a monocapped trigonal pyramidal topology. Variable-temperature magnetic susceptibility measurements on powdered microcrystalline samples of 1 and 5 revealed the existence of antiferromagnetic interactions which led to an S = 5/2 ground state. Mössbauer spectroscopy studies on powdered microcrystalline samples of 1 and 5 confirmed that all iron ions of both complexes are in the Fe 3+ (S = 5/2) state. The variation of the ligand environment in the various iron sites was reflected in their different quadruple splitting parameters. At T < 50 K the Mössbauer spectra indicated the onset of spin relaxation effects in the time scale of the technique (10 -7-10 -8 s). © 2012 The Royal Society of Chemistry.