Synthesis and characterization of three-dimensional-metal carboxylate clusters

Polynuclear, oxide-bridged manganese carboxylate clusters are relevant to areas as diverse as bioinorganic chemistry and magnetic materials. A tetranuclear Mn-oxo aggregate referred to as the water oxidation center (WOC) is known to catalyze the photosynthetic transformation of water to dioxygen in Photosystem II. Despite numerous investigations, an accurate synthetic model of WOC is still lacking. Manganese complexes are also of relevance to new magnetic materials. Specially, some Mn clusters behave as magnets below a critical temperature, each single molecule retains its magnetization when an applied field is removed. These complexes are called single-molecule magnets (SMMs). The requirements for a molecule to be a SMM are large ground-state spin and large and negative magnetic anisotropy.; The reactions of the ligand 1,2-bis(2,2'-bipyridyl-6-yl)ethane (bbe) with the 3d-metals Mn, Co and Ni has been studied. The new species [Mn4O2(O2CR)4(bbe) 2](ClO4)2, [Mn4O2(O 2CR)2(OMe)3(bbe)2(MeOH)](ClO4 )2, [Co8O4(OH)4(O2 CR)6(bbe)2](ClO4)2, [Co(bbe)(ClO 4)2], [Ni2(bbe)(O2CMe)4], [Ni2(CO3)(bbe)2](ClO4)2 and [Ni(bbe)(O2CMe)]ClO4 (R = Me, Et, Ph) were prepared and comparisons were made with the M/bpy complexes. Additionally, in Co and Ni reactions with H2O2, the bbe ligand gets oxidized to give the new bbO- ligand in the complexes [Co 4(bbO)2(O2CMe)4](ClO4) 2 and [Ni2(bbO)(O2CPh)3(H2O)]. Mn/bbe and Mn/bpy chemistry with the novel oxidation agent oxone was investigated. The three Mn(III)/bpy complexes with bridging sulfate groups [Mn2O(O 2CMe)(SO4)(bbe)](PF6), [Mn2(SO 4)2(bpy)2] and [Mn4O2(O 2CMe)4(SO4)2(bpy)2] were prepared. The magnetic properties of these complexes were studied, and they showed how the bis-chelating ligand can impose a geometrical distortion on the coordination sphere of the metals that controls the nature of the magnetic coupling, just like the protein environment would do in the enzyme.; A series of [Mn18] complexes with the chelating ligands hmp - and hep- and carboxylates were synthesized and structurally characterized. These complexes were found to be SMMs and a detailed investigation of their magnetic properties was performed. The new [Mn21O16(O2CMe)16(hmp)6(hmpH) 2(pic)2(py)(H2O)](ClO4)4 complex was synthesized. It is structurally related to the [Mn18] complexes and it is also a SMM. Reaction of bbe with [Mn12O 12(O2CMe)16(H2O)4] afforded the salt [Mn4O2(O2CMe)4(bbe) 2][Mn12O12(O2CMe)16(H 2O)3], an unusual salt of a SMM with a paramagnetic cation.