Homo- and heterometallic manganese clusters: New metal architectures, single-molecule magnets, and physical phenomena

Polynuclear discrete clusters incorporating transition metals have been attracting a lot of attention, due to their aesthetically pleasing chemical structures, and their magnetic properties, such as single-molecule magnetism (SMM); this is a property intrinsic to the individual molecules, which makes them capable of functioning as nanoscale magnetic particles. The first species to exhibit such properties was [Mn12O12(O2CMe) 16(H2O)4] (Mn12), which now serves as the "drosophila" of molecular magnetism. Extension of this chemistry has led to a new high-symmetry Mn12 derivative (Mn 12 tBu) with no intermolecular communication. The thorough investigation of its physical and spectroscopic properties has led to exciting new physics. The use of Mn12 clusters as models has allowed for accurate measurement of the magnetization reversal barriers, with the latter finding addressing several misconceptions about SMMs.;In the synthesis of clusters, organic groups are often used as ligands, such as oximes, which in this work have been used in Mn chemistry either alone or with azide groups known to be ferromagnetic couplers. The use of methyl 2-pyridyl ketone oxime (mpkoH) in combination with azides has afforded a family of half-integer spin hexanuclear SMMs.;Extending this work to the bifunctional form of mpkoH, the use of 2,6-diacetylpyridine oxime has provided an entry into new cluster types, including a pentanuclear family of MnIV 2MnIIIMnII 2 clusters, as well as a MnIV 2Gd III triangular complex with an unusual combination of metal oxidation states. The thorough study of the latter, using both physical and theoretical methods, allowed for spin-frustration effects to be investigated and understood.;Ferromagnetic MnIII 3 triangles have also been important in the recent literature, since some of them behave as SMMs. Thus, a new MnIII 3 triangle was synthesized, from the use of bis(hydroxymethyl)-p-cresol (hmcH3), which is ferromagnetically coupled but not a SMM, which is in contrast with other literature examples. The comprehensive magnetostructural correlation between MnIII 3 triangles has led to insights in the structure / property relationship, and to important conclusions about the origin of ferromagnetism and molecular anisotropy.;Another ligand used in this work is the non-flexible 1,8-naphthalene dicarboxylate, which has afforded a family of Mn13 clusters, resembling the body-centered cubic structure of mineral salts, and the mathematic model of the Archimedian solid, cuboctahedron. A magnetostructural correlation was possible for these Mn13 cages, which proved that small "tweaking" of the structures can affect the magnetic properties, and change the ground states of the molecules.;The incorporation of lanthanides could also lead to novel structures, while high oxidation-state clusters could be potentially useful in the chemical industry instead of metal oxides, i.e. in the catalysis of nitric oxides. To replicate these conditions in a molecule a Ce6Mn4, a Mn4Ce2, and a Mn8Ce clusters were synthesized. The CeIV 6MnIII 2Mn IV 2 complex possesses a central CeIV octahedron, capped by two Mn/Ce cubane units, while the Mn4Ce2 cage is a snub octahedron, both unprecedented structural motifs. This work has also afforded the fifth isolated member of a Mn8Ce family of clusters with a saddle-like topology. From the challenging magnetostructural correlation a previously-ignored magnetic pathway was found to dictate the overall spin ground state, and thus the SMM properties.