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

摘要

A family of wheel-shaped charge-neutral heterometallic {Fe^III4Ln^III2}- and {Fe^III18M^III6}-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 Fe^III 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 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 CH₂Cl₂ in >2, and 2EtOH and 2 CH₂Cl₂ in >3). In >4–>10, the largest 3d/4f wheels currentlyknown, nearly linear Fe₃ fragments are joined via mononuclearLn/Y units by a set of isobutyrates and amino alcohol ligands intovirtually 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).