Further Study of the Linear Trinickel(II) Complex of Dipyridylamide

The title compound, Ni3(dpa)4Cl2 (dpa = di(2-pyridyl)amido anion), first reported 30 years ago, structurally
characterized in 1991, has been obtained in two new crystal forms, Ni3(dpa)4Cl2·2CH2Cl2 (tetragonal, space group
I4̄, with a = 27.3046(7) Å, c = 12.2452(2) Å, Z = 8) and Ni3(dpa)4Cl2·THF (orthorhombic, space group Pccn,
with a = 12.673(1) Å, b = 14.138(3) Å, c = 23.890(2) Å, 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 NiII complexes, (3) the magnetic
moments of the two terminal nickel(II) ions display antiferromagnetic coupling, with 2J = −108 cm-1, and (4)
the Ni3 chain remains symmetrical in solution.