Further study of the linear trinickel(II) complex of dipyridylamide

The title compound, Ni-3(dpa)(4)Cl-2 (dpa = di(2-pyridyl)amido anion), first reported 30 years ago, structurally characterized in 1991, has been obtained in two new crystal forms, Ni-3(dpa)(4)Cl-2. 2CH(2)Cl(2) (tetragonal, space group I (4) over bar, with a = 27.3046(7) Angstrom, c = 12.2452(2) Angstrom, Z = 8) and Ni-3(dpa)(4)Cl-2. THF (orthorhombic, space group Pccn, with a = 12.673(1) Angstrom, b = 14.138(3) Angstrom, c = 23.890(2) Angstrom, Z = 4). They have been examined structurally, and the magnetic properties of one of them determined from, 2 to 300 K. Also the proton NMR spectrum has been recorded. These data allow the following conclusions to be drawn: (1) the molecular structure is invariant in the three crystalline forms and has a symmetrical chain of nickel atoms, (2) the terminal metal atoms each have two unpaired electrons, while the central one is typical of diamagnetic square-planar Ni-II complexes, (3) the magnetic moments of the two terminal nickel(II) ions display antiferromagnetic coupling, with 2J = -108 cm(-1), and (4) the Ni-3 chain remains symmetrical in solution.