Ultralarge 3d/4f Coordination Wheels: From Carboxylate/Amino Alcohol-Supported {Fe(4)Ln(2)} to {Fe(18)Ln(6)} Rings

[Image: see text] A family of wheel-shaped charge-neutral heterometallic {Fe(III)(4)Ln(III)(2)}- and {Fe(III)(18)M(III)(6)}-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)(O(2)CCMe(3))(6)(N(3))(4)(Htea)(4)]·2(EtOH), Ln = Dy (1a), Er (1b), Ho (1c); [Fe(4)Tb(2)(O(2)CCMe(3))(6)(N(3))(4)(Htea)(4)] (1d); [Fe(4)Ln(2)(O(2)CCMe(3))(6)(N(3))(4)(Htea)(4)]·2(CH(2)Cl(2)), Ln = Dy (2a), Er (2b); [Fe(4)Ln(2)(O(2)CCMe(3))(4)(N(3))(6)(Htea)(4)]·2(EtOH)·2(CH(2)Cl(2)), Ln = Dy (3a), Er (3b) and the {Fe(18)M(6)}-type compounds [Fe(18)M(6)(O(2)CCHMe(2))(12)(Htea)(18)(tea)(6)(N(3))(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 Fe(III) pivalate or isobutyrate clusters, lanthanide/yttrium nitrates, and bridging triethanolamine (H(3)tea) and azide ligands in different solvents: EtOH for the smaller {Fe(4)Ln(2)} wheels and MeOH/MeCN or MeOH/EtOH for the larger {Fe(18)M(6)} wheels. Single-crystal X-ray diffraction analyses revealed that 1–3 consist of planar centrosymmetric hexanuclear clusters built from Fe(III) and Ln(III) 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 CH(2)Cl(2) in 2, and 2 EtOH and 2 CH(2)Cl(2) in 3). In 4–10, the largest 3d/4f wheels currently known, nearly linear Fe(3) 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 {Fe(4)Tb(2)} (1d) and slow relaxation for {Fe(4)Ho(2)} (1c), {Fe(18)Dy(6)} (4), and {Fe(18)Tb(6)} (6).