Triangular NiII2LnIII and NiII2YIII complexes derived from di-2-pyridyl ketone: Synthesis, structures and magnetic properties

The synthetic investigation of the Ni-II/M(NO3)(3)center dot 6H(2)O/di-2-pyridyl ketone [(py)(2)CO] tertiary reaction system in EtOH has yielded triangular Ni2M cationic complexes (M = lanthanide, Y). The reaction between Ln(NO3)(3)center dot 6H(2)O, Ni(ClO4)(2)center dot 6H(2)O. (PY)(2)CO and base (1:3:3:3) in EtOH under gentle heating gave the iso-structural complexes [Ni(2)Ln((py)(2)C(OEt)(O))(3){(py)(2)C(OH)(O))(NO3)(H2O)](ClO4)(2) (Ln = Gd, 2; Ln = Tb, 3) in high yields. The ligands (PY)2C(OEt)(O)(-) and (PY)(2)C(OH)(O)(-) are the monoanions of the hemiketal and gem-diol derivatives of (PY)(2)CO, 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 mu O-3-(-) atom of the unique 3.3011 (Harris notation) (PY)(2)C(OH)(O)- ligand. Each metal-metal edge is bridged by the deprotonated 0 atom of one 2.2011 (PY)2C(OEt)(O)(-) ligand. The isostructural complexes [Ni2M{(PY)(2)C(OEt)(O))(4)(NO3)(H2O)](2)-[M(NO3)(5)](ClO4)(2) (M = Y, 4; M = Tb, 5; M = Dy, 6) were prepared by the 1:1 reaction of the mononuclear metalloligand [Ni(O2CMe)((PY)(2)COH(PY)(2)C(OH)(2))](ClO4) (1) and M(NO3)(3)center dot 6H(2)O 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)(0)- ligand of the latter by one 3.3011 (PY)2C(OEt)(0)- group in the former. The Y-III, Tb-III and Dy-III atoms in [M(NO3)(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 center dot center dot center dot Ni and Ni center dot center dot center dot Gd exchange interactions, and an S tau = 11/2 ground state for 2. Complex 3 is characterized by a high-spin ground state while the ferromagnetic Ni center dot center dot center dot 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. (C) 2011 Elsevier Ltd. All rights reserved.