Mononuclear nickel(II) complexes coordinated by polypyridyl ligands

Three mononuclear polypyridyl complexes of Ni(II), [Ni(Ph(2)phen)(3)](PF6)(2)center dot CH3CN (1), [Ni(dpa)(2)(phen)](PF6)(2) (2) and [Ni(bpy)(3)](PF6)(2) (3), where Ph(2)phen is 4,7-diphenyl-1,10-phenanthroline, dpa is 2,2'-dipyridylamine, bpy is 2,2'-bipyridine, and phen is 1,10-phenanthroline, were prepared and their solid state structures determined by single-crystal X-ray crystallography. The structural determination shows that the coordination geometry around the Ni(II) center is a distorted octahedron in each complex. The investigation of synthesis procedure and crystallographic data of complex 3 indicates the spontaneous resolution of supramolecular chirality. A careful inspection of the packing pattern in the lattice of each complex reveals that non-covalent interactions of two different types, viz. C-H center dot center dot center dot F and C-H center dot center dot center dot pi interactions, are active in the lattice. The packing structures of 1-3 also show that the rings of the polypyridyl ligands, Ph(2)phen, dpa, bpy, and phen, are not located face-to-face and can not interact through pi-pi interactions. Cyclic voltammetry data of 1 and 3 show that the Ni(III/II) reduction couple is quasi-reversible and this reduction becomes progressively more difficult on passing from bpy to Ph(2)phen, while complex 2 shows an irreversible behavior with the peak-to-peak separation of about 500 mV. Magnetic susceptibility data derived from paramagnetic NMR revealed effective magnetic moments of 3.12 BM for 1, 3.27 BM for 2, and 3.14 for 3 at room temperature. (C) 2011 Elsevier Ltd. All rights reserved.