Syntheses, crystal structures, and magnetic properties of a family of heterometallic octanuclear [Cu 6 Ln 2 ] (Ln = Dy( iii ), Tb( iii ), Ho( iii ), Er( iii ), and Gd( iii )) complexes

A new family of octanuclear Cu–Ln complexes, [Cu 6 Ln 2 (tea) 2 {(py) 2 CO 2 } 3 Cl 6 ]· x H 2 O (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) 2 CO 2 H 2 = the gem -diol form of di-2-pyridyl ketone, teaH 3 = 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 CuCl 2 ·2H 2 O, Ln(NO 3 ) 3 ·6H 2 O, 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) 2 CO 2 2− and one tea 3− ligands, without the presence of coordinated solvent molecules such as H 2 O and small anions such as NO 3 − 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 M versus T using the Curie–Weiss law and fitting the data of χ M T 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.