Ultralarge 3d/4f Coordination Wheels: From Carboxylate/Amino Alcohol-Supported {Fe4Ln2} to {Fe18Ln6} Rings

A family of wheel-shaped charge-neutral heterometallic {Fe(4)(III)Ln(2)(III)}- and {(Fe1818M6III)-M-III}-type coordination clusters demonstrates the intricate interplay of solvent effects and structure-directing roles of semiflexible bridging ligands. The {Fe(4)Ln(2)}-type compounds [Fe(4)Ln(2)(O2CCMe3)(6)(N-3)(4)(Htea)(4)]center dot 2(EtOH), Ln = Dy (1a), Er (1b), Ho (1c); [Fe4Tb2(O2CCMe3)(6)(N-3)(4)(Htea)(4)] (1d); [Fe(4)Ln(2)(O2CCMe3)(6)(N-3)(4)(Htea)(4)]center dot 2(CH2Cl2), Ln = Dy (2a), Er (2b); [Fe(4)Ln(2)(O2CCMe3)(4)(N-3)(6)(Htea)(4)]center dot(2)(EtOH)center dot(2)(CH2Cl2), Ln = Dy (3a), Er (3b) and the {Fe18M6}-type compounds [Fe18M6(O2CCHMe2)(12)(Htea)(18)(tea)(6)(N-3)(6)]center dot n(solvent), M = Dy (4, 4a), Gd (5), Tb (6), Ho (7), Sm (8), Eu (9), and Y (10) form in ca. 2040% 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 {Fe(4)Ln(2)} wheels and MeOH/MeCN or MeOH/EtOH for the larger {Fe18M6} wheels. Single-crystal X-ray diffraction analyses revealed that 13 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 1ac, 2 CH2Cl(2) in 2, and 2 EtOH and 2 CH2Cl2 in 3). In 410, 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 110 reveal slow magnetization relaxation for {Fe4Tb2} (1d) and slow relaxation for {Fe4Ho2} (1c), {Fe18Dy6} (4), and {Fe18Tb6} (6).