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 [Ni(6)(O(2)CMe)(6){(py)C(H)NO}(6)].H(2)O (1.H(2)O), [Ni(6)(O(2)CPh)(6){(py)C(H)NO}(6)].2EtOH (2.2EtOH), [Ni(6){(4-Cl)O(2)CPh}(6){(py)C(H)NO}(6)].2EtOH (3.2EtOH) and [Mn(6)(O(2)CMe)(6){(py)C(H)NO}(6)].H(2)O (4.H(2)O), where (4-Cl)PhCO(2)(-) is 4-chlorobenzoate. The reactions of M(O(2)CMe)(2).4H(2)O (M = Ni, Mn) with one equivalent of (py)C(H)NOH in EtOH at 120 degrees C under autogenous pressure give isostructural 1.H(2)O and 4.H(2)O. Complexes 2.2EtOH and 3.2EtOH were obtained from the 1 : 1 : 1 Ni(O(2)CMe)(2).4H(2)O/{(py)C(H)NOH/(X)PhCO(2)H 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, syn eta(1):eta(1):mu mode, while the (py)C(H)NO(-) ions behave as eta(1):eta(1):eta(2):mu(3) ligands. Each metal...metal vector is bridged by one carboxylate group, one mu-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.