Triangular Ni II2Ln III and Ni II2Y III complexes derived from di-2-pyridyl ketone: Synthesis, structures and magnetic properties

Abstract

The synthetic investigation of the Ni II/M(NO 3) 3·6H 2O/di-2-pyridyl ketone [(py) 2CO] tertiary reaction system in EtOH has yielded triangular Ni 2M cationic complexes (M = lanthanide, Y). The reaction between Ln(NO 3) 3·6H 2O, Ni(ClO 4) 2·6H 2O, (py) 2CO and base (1:3:3:3) in EtOH under gentle heating gave the isostructural complexes [Ni 2Ln{(py) 2C(OEt)(O)} 3{(py) 2C(OH)(O)}(NO 3)(H 2O)](ClO 4) 2 (Ln = Gd, 2; Ln = Tb, 3) in high yields. The ligands (py) 2C(OEt)(O) − and (py) 2C(OH)(O) − are the monoanions of the hemiketal and gem-diol derivatives of (py) 2CO, respectively, formed in situ in the presence of the metal ions. The cations of 2 and 3 consist of one 8-coordinate Ln III and two distorted octahedral Ni II atoms in an essentially isosceles, triangular arrangement capped by a central μ 3-Ο − atom of the unique 3.3011 (Harris notation) (py) 2C(OH)(O) − ligand. Each metal–metal edge is bridged by the deprotonated O atom of one 2.2011 (py) 2C(OEt)(O) − ligand. The isostructural complexes [Ni 2M{(py) 2C(OEt)(O)} 4(NO 3)(H 2O)] 2[M(NO 3) 5](ClO 4) 2 (M = Y, 4 ; M = Tb, 5 ; M = Dy, 6) were prepared by the 1:1 reaction of the mononuclear “metalloligand” [Ni(O 2CMe){(py) 2CO}{(py) 2C(OH) 2}](ClO 4) ( 1) and M(NO 3) 3·6H 2O in EtOH under mild heating in moderate to good yields. The structures of the dications of 4– 6 are similar to those in 2 and 3, the only difference being the replacement of the unique 3.3011 (py) 2C(OH)(O) − ligand of the latter by one 3.3011 (py) 2C(OEt)(O) − group in the former. The Y III, Tb III and Dy III atoms in [M(NO 3) 5] 2− are coordinated by five bidentate chelating nitrato groups. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the ligands. Variable temperature, solid-state direct current magnetic susceptibility and magnetization studies were carried out on dried samples of 2– 4. The data indicate ferromagnetic Ni⋯Ni and Ni⋯Gd exchange interactions, and an S T = 11/2 ground state for 2. Complex 3 is characterized by a high-spin ground state while the ferromagnetic Ni⋯Ni interaction for 2 is independently supported by the study of 4. No out-of-phase, alternating current susceptibility signals have been detected for 3 that would be indicative of SMM behavior.