A family of wheel-shaped charge-neutral heterometallic {FeIII4LnIII2}- and {FeIII18MIII6}-type coordination clusters demonstrates the intricate interplay of solvent effects and structure-directing roles of semiflexible bridging ligands. The {Fe4Ln2}-type compounds [Fe4Ln2(O2CCMe3)6(N3)4(Htea)4]·2(EtOH), Ln = Dy (1a), Er (1b), Ho (1c); [Fe4Tb2(O2CCMe3)6(N3)4(Htea)4] (1d); [Fe4Ln2(O2CCMe3)6(N3)4(Htea)4]·2(CH2Cl2), Ln = Dy (2a), Er (2b); [Fe4Ln2(O2CCMe3)4(N3)6(Htea)4]·2(EtOH)·2(CH2Cl2), Ln = Dy (3a), Er (3b) and the {Fe18M6}-type compounds [Fe18M6(O2CCHMe2)12(Htea)18(tea)6(N3)6]·n(solvent), M = Dy (4, 4a), Gd (5), Tb (6), Ho (7), Sm (8), Eu (9), and Y (10) form in ca. 20–40% yields in direct reaction of trinuclear FeIII pivalate or isobutyrate clusters, lanthanide/yttrium nitrates, and bridging triethanolamine (H3tea) and azide ligands in different solvents: EtOH for the smaller {Fe4Ln2} wheels and MeOH/MeCN or MeOH/EtOH for the larger {Fe18M6} wheels. Single-crystal X-ray diffraction analyses revealed that 1–3 consist of planar centrosymmetric hexanuclear clusters built from FeIII and LnIII ions linked by an array of bridging carboxylate, azide, and aminopolyalcoholato-based ligands into a cyclic structure with a cavity, and with distinct sets of crystal solvents (2 EtOH per formula unit in 1a–c, 2 CH2Cl2 in 2, and 2 EtOH and 2 CH2Cl2 in 3). In 4–10, the largest 3d/4f wheels currently known, nearly linear Fe3 fragments are joined via mononuclear Ln/Y units by a set of isobutyrates and amino alcohol ligands into virtually planar rings. The magnetic properties of 1–10 reveal slow magnetization relaxation for {Fe4Tb2} (1d) and slow relaxation for {Fe4Ho2} (1c), {Fe18Dy6} (4), and {Fe18Tb6} (6).
Trinuclear μ-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 (mdeaH)[FeO(thme)Cl]·0.5(MeCN)·0.5(HO) (1), [FeO(OH)(teda)(N)(MeO)]N(NO)(MeO)·2.5(HO) (2), [FeO(teda)Cl]·6(CHCl) (3), [FeO(OH)(OCCHMe)(bdea)(EtO)(HO)]·2(EtOH)·5(MeCN)·6(HO) (4), and [FeO(OH)(OCCHMe)(mdea)(EtO)(HO)](NO)·EtOH·HO (5), where tedaH = N, N, N', N'-tetrakis(2-hydroxyethyl)ethylenediamine; thmeH = 1,1,1-tris(hydroxymethyl)ethane; mdeaH = N-methyldiethanolamine; and bdeaH = N-butyldiethanolamine. Complete carboxylate metathesis in the {Fe} precursor complexes by thme or teda and the agglomeration of the formed species under solvothermal conditions afforded carboxylate-free {Fe} product (1) in MeCN/CHCl or {Fe} complexes (2 and 3) in MeOH/EtOH and CHCl/thf, respectively (thf = tetrahydrofuran). Single-crystal X-ray diffraction analyses revealed that 1 contains a [FeO(thme)Cl] cluster anion with a Lindqvist-type {Fe(μ-O)} core motif, charge-compensated by two protonated mdeaH cations. 2 comprises a [FeO(OH)(teda)(N)(MeO)] cation with a {FeO(OH)} core, whereas 3 contains a charge-neutral [FeO(teda)(Cl)] complex with an {FeO} core. Finally, employing flexible bdeaH or mdeaH ligands under soft reaction conditions afforded giant {Fe} oxo-hydroxo complexes (4 and 5) with a central {Fe} layer sandwiched between two outer {Fe} groups. Magnetic studies of 1-5 revealed strong antiferromagnetic coupling between the Fe spin centers in all clusters.
A series of new octanuclear propeller-like aminoalcohol-supported Fe(III) oxocarboxylate coordination clusters, [Fe8O3(O2CCHMe2)9(tea)(teaH)3]·MeCN·2(H2O) (1), [Fe8O3(O2CCHMe2)6(N3)3(tea)(teaH)3] (2), [Fe8O3(O2CCMe3)6(N3)3(tea)(teaH)3]·0.5(EtOH) (3), and [Fe8O3(O2CCHMe2)6(N3)3(mdea)3(MeO)3] (4) (where teaH3 = triethanolamine; mdeaH2 = N-methyldiethanolamine) has been isolated and magnetochemically analyzed combining the programs wxJFinder and CONDON in an approach to avoid overparameterization issues that are common to larger spin polytopes. Dominant antiferromagnetic exchange interactions exist in all clusters along the edges of the propellers, while moderate ferromagnetic interactions are found along the propeller axes in their {Fe8O3} metallic cores.
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