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

A family of wheel-shaped charge-neutral heterometallic {FeLn}- and {FeM}-type coordination clusters demonstrates the intricate interplay of solvent effects and structure-directing roles of semiflexible bridging ligands. The {FeLn}-type compounds [FeLn(OCCMe)(N)(Htea)]·2(EtOH), Ln = Dy (1a), Er (1b), Ho (1c); [FeTb(OCCMe)(N)(Htea)] (1d); [FeLn(OCCMe)(N)(Htea)]·2(CHCl), Ln = Dy (2a), Er (2b); [FeLn(OCCMe)(N)(Htea)]·2(EtOH)·2(CHCl), Ln = Dy (3a), Er (3b) and the {FeM}-type compounds [FeM(OCCHMe)(Htea)(tea)(N)]·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 pivalate or isobutyrate clusters, lanthanide/yttrium nitrates, and bridging triethanolamine (Htea) and azide ligands in different solvents: EtOH for the smaller {FeLn} wheels and MeOH/MeCN or MeOH/EtOH for the larger {FeM} wheels. Single-crystal X-ray diffraction analyses revealed that 1-3 consist of planar centrosymmetric hexanuclear clusters built from Fe and Ln 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 CHCl in 2, and 2 EtOH and 2 CHCl in 3). In 4-10, the largest 3d/4f wheels currently known, nearly linear Fe 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 {FeTb} (1d) and slow relaxation for {FeHo} (1c), {FeDy} (4), and {FeTb} (6).