Tuning the Condensation Degree of {FeIIIn} Oxo Clusters via Ligand Metathesis, Temperature, and Solvents.

Trinuclear μ3-oxo-centered iron(III) isobutyrate clusters readily react with polyalcohol organic ligands under one-pot synthesis conditions. Depending on the ligand, solvent, and temperature, a range of hexa-, dodeca-, and doicosanuclear iron(III) oxo-hydroxo condensation products, isolated as (mdeaH3)2[Fe6O(thme)4Cl6]·0.5(MeCN)·0.5(H2O) (1), [Fe12O4(OH)2(teda)4(N3)4(MeO)4]N3(NO3)0.5(MeO)0.5·2.5(H2O) (2), [Fe12O6(teda)4Cl8]·6(CHCl3) (3), [Fe22O16(OH)2(O2CCHMe2)18(bdea)6(EtO)2(H2O)2]·2(EtOH)·5(MeCN)·6(H2O) (4), and [Fe22O14(OH)4(O2CCHMe2)18(mdea)6(EtO)2(H2O)2](NO3)2·EtOH·H2O (5), where tedaH4 = N, N, N', N'-tetrakis(2-hydroxyethyl)ethylenediamine; thmeH3 = 1,1,1-tris(hydroxymethyl)ethane; mdeaH2 = N-methyldiethanolamine; and bdeaH2 = N-butyldiethanolamine. Complete carboxylate metathesis in the {Fe3} precursor complexes by thme3- or teda4- and the agglomeration of the formed species under solvothermal conditions afforded carboxylate-free {Fe6} product (1) in MeCN/CH2Cl2 or {Fe12} complexes (2 and 3) in MeOH/EtOH and CHCl3/thf, respectively (thf = tetrahydrofuran). Single-crystal X-ray diffraction analyses revealed that 1 contains a [Fe6O(thme)4Cl6]2- cluster anion with a Lindqvist-type {Fe6(μ6-O)} core motif, charge-compensated by two protonated mdeaH3+ cations. 2 comprises a [Fe12O4(OH)2(teda)4(N3)4(MeO)4]2+ cation with a {Fe12O4(OH)2}26+ core, whereas 3 contains a charge-neutral [Fe12O6(teda)4(Cl)8] complex with an {Fe12O6}24+ core. Finally, employing flexible bdeaH2 or mdeaH2 ligands under soft reaction conditions afforded giant {Fe22} oxo-hydroxo complexes (4 and 5) with a central {Fe6} layer sandwiched between two outer {Fe8} groups. Magnetic studies of 1-5 revealed strong antiferromagnetic coupling between the FeIII spin centers in all clusters.