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

Abstract

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 NiII 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 NiIIatoms 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 NiIIatoms 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 (ΧM″) signals at temperatures below ∼3.5 K

complex 2 reveals no ΧM″ 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. © 2010 American Chemical Society.