Solvent-Dependent Access to Two Different Ni4II Core Topologies from the First Use of Pyridine-2,6-dimethanol in Nickel(II) Cluster Chemistry

The use of pyridine-2,6-dimethanol, pdmH(2), in reactions with nickel(II) acetate has led to two Ni-4 clusters, depending on the solvent. [Ni-4(O2CMe)(4)(pdm(H))(4)]center dot MeCN (1 center dot MeCN) can be obtained from MeCN and [Ni-4(O2CMe)(6)(pdmH)(2)(EtOH)(2)]center dot 1.2EtOH (2-1.2EtOH) from EtOH. Each cluster can be converted into the other in the appropriate solvent. The tetranuclear cluster molecule 1 possesses a distorted cubane {Ni-4(mu(3)-OR)(4)}(4+) core (RO- = pdmH(-)) with the Ni-II atoms and the alkoxide-type oxygen atoms from the eta(3) : eta(1) : mu(3) pdmH(-) ligands occupying alternate vertices of the cube; four mu(1) : mu(1) : mu MeCO2- groups cap four faces of the cube. The four Ni-II atoms in molecule 2 are located at four vertices of a defective dicubane and are bridged by six oxygen atoms, two mu(3) from the eta(3) : eta(1) : eta(1) : mu(3) pdmH(-) ligands and four from four monoatomically bridging MeCO2- groups; peripheral ligation is provided by two eta(1) : eta(1) : mu MeCO2- groups and two terminal EtOH ligands. IR data are discussed in terms of the coordination modes of the ligands. Variable-temperature direct-current magnetic susceptibility data of 1 and 2 were modelled with two and three J values respectively, indicating diamagnetic ground states (S = 0). The sign and the magnitude of the J values are discussed in terms of structural features of the complexes.