Two types of Ln2Cu2 hydroxo-trimethylacetate complexes with 0D and 1D motifs: synthetic features, structural differences, and slow magnetic relaxation

Abstract

Two series of heterometallic Ln^III–Cu^II compounds containing a butterfly-like tetranuclear metal core were synthesized and characterized by X-ray diffraction and magnetometry. The structures of the new compounds were shown to depend on the nature of the hydroxide used for the synthesis. The reactions of copper(II) and lanthanide(III) salts with Hpiv (Hpiv is trimethylacetic acid) and LiOH in a MeCN–EtOH mixture afford the molecular complexes [Ln₂Cu₂(μ₃-OH)₂(piv)₈(H₂O)₄]·4EtOH (1_Ln, Ln = Gd, Tb, Dy, Ho, Yb), whereas the similar reactions using NaOH instead of LiOH give the 1D coordination polymers [Na₂Ln₂Cu₂(μ₃-OH)₂(piv)₁₀(EtOH)₂]·EtOH (2_Ln, Ln = Gd, Tb, Dy, Ho, Yb). According to ac susceptibility measurements, the Dy^III–Cu^II compounds (1_Dy and 2_Dy) exhibit slow relaxation of magnetization indicative of single-molecule magnet (SMM) behavior. In the series of Yb^III–Cu^II compounds, only complex 2_Yb shows frequency-dependent out-of-phase ac susceptibility signals. This is the first reported example of carboxylate-based Yb^III–Cu^II compound displaying slow magnetic relaxation.