Synthesis, Magnetic Properties, and X-ray Spectroscopy of Divalent Cobalt(II) and Nickel(II) Cubanes [M-4(II)(HL2)(4)(OAc)(4)]

Abstract

Under anaerobic conditions, the reactions of cobalt(II) and nickel(II) acetate tetrahydrate with 2,6-pyridinedimethanol (H2L2, 3) in anhydrous acetonitrile afforded two tetranuclear metal(II) complexes [M-4(II)(HL2)(4)(OAc)(4)] (4; M-II = Co2+, Ni2+) with a [M-4(mu(3)-O)(4)](4+) cubane core. X-ray structural analyses revealed that both MII cubanes 4a center dot 2CH(3)OH and 4b center dot 2CH(3)OH are isostructural and crystallize in the tetragonal space group I4(1)/acd with eight molecules in the unit cell. In the solid state, the orientation of the cubane cores of 4 and the formation of a 3D framework were controlled by pi-pi interactions as well as intra- and intermolecular O-H center dot center dot center dot O hydrogen bonds. Variable-temperature magnetic susceptibility measurements revealed that the cubanes 4 show a ferrimagnetic coupling scheme that leads to a diamagnetic ground state for both complexes. Core-level X-ray photoelectron spectroscopy confirmed that the Co and Ni ions in 4a and 4b are in a divalent state. X-ray magnetic circular dichroism was performed to extract the spin and orbital contributions to the Co and Ni magnetic moments. We compared the experimental results of the local electronic structures around the Co2+ ions in 4a and the Ni2+ ions in 4b with charge-transfer multiplet simulations.