E0022

John Bacsa, Hanhua Zhao, Eric J. Schelter and Kim Dunbar, Department of Chemistry, Texas A&M University, College Station, Texas 77842-3012, USA, fax: 979-845-7177, e-mail: jbacsa@mail.chem.tamu.edu.

Structures of a variety of new clusters with different nuclearities and combinations of oxidation states are discussed. The driving force of this research is to understand coupling between closely spaced metal centers and the understanding of single-molecule magnetic behavior. We prepared two new structural isomers with the formula [Mn₁₂O₁₂(CF₃CO₂)₁₆(H₂O)₄]. The direction and magnitude of Jahn-Teller distortion was found to have a profound effect on their magnetic behavior. We have also prepared a tetranuclear Mn complex ([Mn₄(C₅H₄NCH₂O)(O₂CF₃)₄]) in which two of the four manganese ions are assigned as Mn^III and the other two as Mn^II. The Mn^III ions exhibit strong tetragonal elongation along the axial directions while the seven Mn-L bond distances of Mn^III are all similar. The two Mn^III ions are aligned so that their Jahn-Teller axes are oriented parallel to each other, and the maximum distortion of both these ions occurs in the same direction.

Another type of cluster that we are exploring are octanuclear cyanide-bridged complexes formulated as [Re(triphos)(CN)₃]₄[MCl]₄ (M = Mn, Fe, Co, Ni and Zn). These unusual clusters are closed cages resembling cubes with octahedral Re and tetrahedral M atoms at the vertices. The steric demand of the Re complexes appear to enforce tetrahedral coordination at the M atoms. The magnetic properties of these clusters show antiferromagnetic coupling of the metal centers at low temperatures (~25 K) with different overall spin states depending on the identity of M. These clusters are a new family of large spin clusters combining 3d and 5d metal ions with the potential to exhibit interesting magnetic or mixed (electronic, photophysical) properties.

[Mn4(C5H4NCH2O)(O2CF3)4] 1