Exploring the Coordination Chemistry of Hydroxy Alkyl Pyridine and Pyrazine Ligands in 3d Cluster Chemistry

Abstract

Three potentially chiral alkoxide ligands, α-methyl-2-pyridine-methanol (mpmH), dimethyl-2-pyridine-methanol (dmpmH) and methyl-2-pyrazine-methanol (mpzmH), are presented together with select 3d ions for the synthesis and study of three novel polynuclear clusters. The first, a {Ni7} complex prepared from chiral-mpmH, has a unique capped trigonal prismatic topology. Magnetostructural studies reveal that at low temperature it has an S = 0 spin ground state and is not an SMM. The second two complexes are both prepared from rac-dmpmH under the same reaction conditions. Dark green, single crystals, of the kinetic product, a {Ni6} cluster were isolated after 2 weeks. This cluster has a structural topology, comprising four edge-sharing cubanes with missing vertices. Magnetostructual studies reveal the cluster is spin frustrated with an S = 2 ground state at low temperature. AC magnetic susceptibility studies are consistent with field induced SMM properties. After two months, blue plates of a {Ni8} cluster, the thermodynamic product, were obtained. The magnetic core of this cluster has a trapezoidal prismatic topology, containing bridging methyl tetrazolate (mtz−) ligands formed via the in situ, NiII-assisted click reaction between the N3− ions and the MeCN solvent. Reaction of mpzmH with Mn benzoate in the presence of azide ions afforded single crystals of a large mixed valence nanosized {Mn22} cluster which has a pyramidal like structural topology comprised of three layers of Mn4O4 and Mn3O4. DC studies are consistent with the presence of 10 MnII and 12 MnIII ions and the presence of dominant antiferromagnetic interactions at low temperature. AC studies reveal an increase in the in-phase susceptibility (χ′) upon cooling, reaching a broad maximum around 4 K, and the emergence of an out-of-phase component (χ″) below 7 K. However, the sample shows very little frequency dependence to the position of the maximum in χ″. Below 2 K there is the beginnings of an uptick in χ″ suggesting the presence of two distinct relaxation processes. The ac data is complex, and not consistent with the slow relaxation behavior typically observed in polynuclear 3d-SMMs.