Wheel-like Mn-6(II) and Ni-6(II) complexes from the use of 2-pyridinealdoxime and carboxylates

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(O2CMe)(6){(py)C(H)NO}(6)]center dot H2O(1 center dot H2O), [Ni-6(O2CPh)(6){(py)C(H)NO}(6)]center dot 2EtOH (2 center dot 2EtOH), [Ni-6{(4-Cl)O2CPh}(6){(py)C(H)NO}(6)]center dot 2EtOH (3 center dot 2EtOH) and [Mn-6(O2CMe)(6){(py)C(H)NO}(6)]center dot H2O (4 center dot H2O), where (4-Cl)PhCO2- is 4-chlorobenzoate. The reactions of M(O2CMe)(2)center dot 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 center dot H2O and 4 center dot H2O. Complexes 2 center dot 2EtOH and 3 center dot 2EtOH were obtained from the 1 : 1 : 1 Ni(O2CMe)(2)center dot 4H(2)O/{(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, 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 center dot center dot center dot 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 center dot center dot center dot 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.