Oxidation of Ni3(dpa)4Cl2 and Cu3(dpa)4Cl2:: Nickel-nickel bonding interaction, but no copper-copper bonds

Of the known trinuclear dipyridylamido complexes of the first-row transition metals, M-3(dpa)(4)Cl-2 (dpa is the anion of di(2-pyridyl)amine, M = Cr, Co, Ni, Cu), the one-electron-oxidation products of only Cr-3(dpa)(4)Cl-2 and Co-3(dpa)(4)Cl-2 have been isolated previously. Here we report one-electron-oxidation products of Ni-3(dpa)(4)Cl-2 (1) and Cu-3(dpa)(4)-Cl-2 (3): Ni-3(dpa)(4)(PF6)(3) (2) and [Cu-3(dpa)(4)Cl-2]SbCl6 (4). While there are no Ni-Ni bonds in 1, the Ni-Ni distances in 2 are 0.15 Angstrom shorter than those in 1, very suggestive of metal-metal bonding interactions. In contrast, the oxidation of 3 to 4 is accompanied by a lengthening of the Cu-Cu distances, as expected for an increase in electrostatic charge between positively charged nonbonded metal ions, which is further evidence against Cu-Cu bonding in either 3 or 4. A qualitative model of the electronic structures of all [M-3(dpa)(4)Cl-2](n+) (n = 0, 1) compounds is presented and discussed.