The first non-acetato members of the bis(anion)octacarboxylatotetrakis{di-2-pyridyl-methanediolate(−2)}enneametal(II) family of complexes: Synthesis, X-ray structures and magnetism of [M9(N3)2(O2CCMe3)8{(py)2CO2}4] (M = Co, Ni)

The combined use of di-2-pyridyl ketone [(py)2CO] and azides (N3−) in nickel(II) and cobalt(II) pivalate chemistry has afforded complexes [Ni9(N3)2(O2CCMe3)8{(py)2CO2}4] (1) and [Co9(N3)2(O2CCMe3)8{(py)2CO2}4] (2), where (py)2CO22− is the gem-diolate(−2) form of (py)2CO. The complexes are isostructural and crystallize in the monoclinic P21/c space group. Their molecular structures consist of nine metal(II) ions, eight of which are arranged as two parallel squares flanking the ninth. DC magnetic susceptometry on powdered samples of 1 (1-p) reveal an overall antiferromagnetic behavior, leading to an S = 0 ground state. AC susceptometry reveals out-of-phase signals between 10 and 27 K, and ZFC and FC experiments show a divergence of the two curves below ∼27 K. Magnetization-decay and field-sweep experiments verify the relaxation behavior of the sample. Samples of the complex arising from carefully washed single crystals (1-cr) reveal a similar DC behavior, without however the appearance of cusps in the χΜΤ versus T curves, and no relaxation. The relaxation behavior has been assigned to NiO impurities. The results illustrate the extreme care that should be taken when examining the magnetic properties of apparently analytically pure materials obtained under heating. Complex 2 exhibits an overall antiferromagnetic behavior, without observation of any relaxation phenomena.

Graphical abstractThe enneanuclear NiII and CoII complexes with general formula [M9(N3)2(O2CCMe3)8{(py)2CO2}4], are the first non-acetato members of this family, extending this type of chemistry to new and potentially interesting molecular magnetic materials.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Extension of the [M9(N3)2(O2CR)8{(py)2CO2}4] chemistry to various R groups. ► Peripheral ligands affect magnetic coupling without structural variation. ► In NiII chemistry, care is required to obtain samples free of NiO impurities.