Syntheses, crystal structures, and magnetic properties of a family of heterometallic octanuclear [Cu6Ln2] (Ln = Dy(iii), Tb(iii), Ho(iii), Er(iii), and Gd(iii)) complexes

Abstract

A new family of octanuclear Cu–Ln complexes, [Cu₆Ln₂(tea)₂{(py)₂CO₂}₃Cl₆]·xH₂O (Ln = Dy (1), Tb (2), Ho (3), Er (4), Gd (5); x = 1 for 1, 3 and 5, x = 0 for 2 and x = 7 for 4; (py)₂CO₂H₂ = the gem-diol form of di-2-pyridyl ketone, teaH₃ = triethanolamine), has been synthesized and characterized by single-crystal X-ray diffraction, elemental analyses, IR and magnetic properties. These complexes are all isostructural and were obtained by following a self-assembly reaction involving CuCl₂·2H₂O, Ln(NO₃)₃·6H₂O, di-2-pyridyl ketone, triethanolamine and triethylamine in acetonitrile at room temperature. Single-crystal X-ray diffraction analyses indicate that the Ln^III ions in these complexes are seven-coordinate, which is rare in 3d–4f complexes and 4f complexes. The geometries of Ln^III in these complexes severely deviate from capped octahedrons. Moreover, coordination sites of Ln were occupied by two (py)₂CO₂²⁻ and one tea³⁻ ligands, without the presence of coordinated solvent molecules such as H₂O and small anions such as NO₃⁻ ions, which is also rare in 4f ions complexes. The direct-current magnetic susceptibilities show that the ferromagnetic coupling interactions between Cu^II and Ln ions are presented by fitting the data of 1/χ_Mversus T using the Curie–Weiss law and fitting the data of χ_MT versus T of 5 (Gd) using PHI program. AC magnetic measurements of 1–5 without dc field and 2000 Oe dc fields show no temperature- and frequency-dependent signals, which may be due to the low symmetry of the coordination configuration of Ln in these complexes.