Combining azide, carboxylate, and 2-pyridyloximate ligands in transition-metal chemistry: Ferromagnetic NiII 5clusters with a bowtie skeleton

Article abstract of DOI:10.1021/ic1014829

The combined use of the anion of phenyl(2-pyridyl)ketone oxime (ppko^-) and azides (N₃ ^-) in nickel(II) carboxylate chemistry has afforded two new Ni^II ₅clusters, [Ni₅(O₂CR′)₂(N₃)₄(ppko)₄(MeOH)₄] [R′ = H (1), Me (2)]. The structurally unprecedented {Ni₅(μ-N₃)₂(μ₃-N₃)₂}⁶⁺cores of the two clusters are almost identical and contain the five Ni^IIatoms in a bowtie topology. Two N₃ ^-ions are end-on doubly bridging and the other two ions end-on triply bridging. The end-on μ₃-N₃ ^-groups link the central Ni^IIatoms with the two peripheral metal ions on either side of the molecule, while the Ni···Ni bases of the triangles are each bridged by one end-on μ-N₃ ^-group. Variable- temperature, solid-state direct-(dc) and alternating-current (ac) magnetic susceptibility, and magnetization studies at 2.0 K were carried out on both complexes. The data indicate an overall ferromagnetic behavior and an S = 5 ground state for both compounds. The ac susceptibility studies on 1 reveal nonzero, frequency-dependent out-of-phase (Χ_M″) signals at temperatures below ～3.5 K; complex 2 reveals no Χ_M″ signals. However, single-crystal magnetization versus dc field scans at variable temperatures and variable sweep rates down to 0.04 K on 1 reveal no noticeable hysteresis loops, except very minor ones at 0.04 K assignable to weak intermolecular interactions propagated by nonclassical hydrogen bonds.