Hexanuclear complexes from the use of a series of amino-alcohol ligands in Fe chemistry

Abstract

Eight novel FeIII6 clusters with the amino-alcohol ligands 3-amino-1-propanol (apH), N-hydroxyethylpiperidine (N-hepipH), 2-hydroxyethylpiperidine (2-hepipH), 2-aminobenzylalcohol (2-abzaH), N-hydroxyethylmorpholine (N-hemorH) and ethanolamine (eaH), [Fe 6O2(OH)2L2((CH3) 3CCO2)10] (LH = apH, 1

N-hepipH, 2

2-hepipH, 3

2-abzaH, 4}, [Fe6O2(OH)2(N-hemor) 2((CH3)3CCO2)8(CH 3CO2)2]·2MeCN (5·2MeCN), [Fe 6O2(OH)2(N-hemor)3((CH 3)3CCO2)9]·MeCN (6·MeCN), [Fe6O2(ea)6((CH 3)3CCO2)6(N3) 2]·2MeCN (7·2MeCN) and [Fe6O 3(N-hepip)3(PhCO2)9(PhCO 2H)2]·5MeCN (8·5MeCN) are reported. Compound 1 was prepared from the reaction of [Fe3O((CH3) 3CCO2)6(H2O)2(OH)]H 2O with apH in the presence of NaClO4 in MeCN. Accordingly, compounds 2-4 and 6 were prepared from reactions of trinuclear carboxylate Fe3+ clusters with the aminoalcohol ligands whereas the isolation of 5, involved also the addition of Fe(CH3CO 2)2 to the reaction mixture. By using a similar synthetic procedure, but in the presence of N3- ligand, compound 7 was isolated. Finally, the replacement of pivalates with benzoates in the reaction mixture yielded compound 8. To the best of our knowledge, 3, 5 and 6 are the first reported examples containing the ligands 2-hepipH and N-hemorH. Compounds 1-6 are composed of a [Fe6(μ3-O) 2(μ-OH)2]12+ structural core, where the two subunits are either arranged trans to each other (1-5), or they adopt the cis conformation (6). Compounds 7 and 8 possess the [Fe6(μ 3-O)2(μ-OR)6]8+ and [Fe 6(μ3-O)3]12+ structural cores respectively which display topologies rarely found in Fe cluster chemistry. Variable-temperature magnetic susceptibility measurements on powdered microcrystalline samples of 4, 6, 7 and 8 revealed the existence of antiferromagnetic exchange interactions which lead to an ST = 5 for 4 and 7, and diamagnetic ground states (ST = 0) for 6 and 8. Mössbauer spectroscopy studies on powdered microcrystalline samples of 7 and 8 confirmed that all iron ions of both complexes are in the Fe3+ (S = 5/2) state. The variation of the ligand environment in the various iron sites was reflected in their different quadrupole splitting parameters. © 2013 Elsevier Ltd. All rights reserved.