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

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).