Wheel-like MnII6 and NiII6 complexes from the use of 2-pyridinealdoxime and carboxylates

Abstract

The employment of 2-pyridinealdoxime, (py)C(H)NOH, in nickel(II) and manganese(II) carboxylate chemistry under solvothermal conditions is reported. The syntheses, crystal structures and magnetochemical characterization (for two representative compounds) are described for [Ni₆(O₂CMe)₆{(py)C(H)NO}₆]·H₂O (1·H₂O), [Ni₆(O₂CPh)₆{(py)C(H)NO}₆]·2EtOH (2·2EtOH), [Ni₆{(4-Cl)O₂CPh}₆{(py)C(H)NO}₆]·2EtOH (3·2EtOH) and [Mn₆(O₂CMe)₆{(py)C(H)NO}₆]·H₂O (4·H₂O), where (4-Cl)PhCO₂⁻ is 4-chlorobenzoate. The reactions of M(O₂CMe)₂·4H₂O (M = Ni, Mn) with one equivalent of (py)C(H)NOH in EtOH at 120 °C under autogenous pressure give isostructural 1·H₂O and 4·H₂O. Complexes 2·2EtOH and 3·2EtOH were obtained from the 1 : 1 : 1 Ni(O₂CMe)₂·4H₂O/{(py)C(H)NOH/(X)PhCO₂H reaction mixtures in EtOH under solvothermal conditions (X = H, 4-Cl). The structurally similar clusters 1–4 have a wheel-like topology with the six metal ions in a chair conformation. Each metal site is bound to four oxygen and two nitrogen atoms; the donor atoms come from two carboxylate oxygens, two oximate oxygens, one pyridyl nitrogen and one oximate nitrogen atom. The carboxylate ligands show the syn, synη¹:η¹:μ mode, while the (py)C(H)NO⁻ ions behave as η¹:η¹:η²:μ₃ ligands. Each metal⋯metal vector is bridged by one carboxylate group, one μ-O derived from a (py)C(H)NO⁻ ligand and by one diatomic oximate–NO– group from an adjacent (py)C(H)NO⁻ group. The IR spectra of the complexes are discussed in terms of the coordination modes of the ligands. Variable-temperature, solid-state dc magnetic susceptibility studies were carried out on polycrystalline samples of 1 and 4. The data in the 2.0–300 K range have been fit to a model with one J value revealing moderate (1) or weak (2) antiferromagnetic M^II⋯M^II exchange interactions. This work demonstrates the synthetic potential of combining (py)C(H)NOH with carboxylate ligands and the usefulness of solvothermal techniques in 3d-metal cluster chemistry.