Polynuclear lanthanide (Ln) complexes of a tri-functional hydrazone ligand – mononuclear (Dy), dinuclear (Yb, Tm), tetranuclear (Gd), and hexanuclear (Gd, Dy, Tb) examples

Abstract

The lanthanide coordination chemistry of a tri-functional vanillin–hydrazone–oxime ligand reveals a variety of different products, depending on reaction conditions, with mono-nuclear (Dy), dinuclear (Yb, Tm), tetranuclear (Gd) and hexanuclear (Gd, Tb, Dy) examples. The Ln₆ (Ln = Gd, Dy, Tb) complexes form in the presence of both triethylamine and acetic acid, and have unique, flat hexanuclear structures built on a μ₃-O bridged triangular core, with the six lanthanide ions bridged further through μ-acetate and μ-O_hydrazone connections in an expanded fused triangular array. Similar reaction conditions with Yb(III) and Tm(III) lead preferentially to dinuclear systems, while in the presence of a competitive benzoate ligand a rectangular Gd₄ complex results. Variable temperature DC magnetic data for the Gd(III) complexes reveal weak antiferromagnetic exchange. AC magnetic data on the other polynuclear complexes down to 2 K, both in the absence and presence of external bias fields, revealed no significant out of phase signals normally indicative of SMM behavior. However, the mononuclear Dy(III) complex shows frequency dependent AC signals and maxima in the temperature range 2–20 K in the presence of an external bias field, indicative of SMM behaviour, with U_eff = 36(1) K, and τ₀ = 4.4(2) × 10⁻⁶ s.