Slow Magnetic Relaxation and Charge-Transfer in Cyano-Bridged Coordination Clusters Incorporating [Re(CN)7]3-/4-

Treatment of the cyanometalate building unit [Re(CN)(7)](3-) with [(PY5Me(2))M(MeCN)](2+) (M = Co, Ni, Cu) affords a series of pentanuclear clusters of formulas [(PY5Me(2))(4)M4Re(CN)(7)](5+) (M = Co, Ni, Cu) and [(PY5Me(2))(4)Cu4Re(CN)7](4). Single crystal X-ray diffraction analyses of the clusters reveal a star-like structure in which four [(PY5Me2)M](2+) moieties are linked to a central [Re(CN)(7)](3-) unit via bridging cyanide ligands. An intramolecular Co-ll -> Re-IV charge-transfer accompanies the formation of the (CoIIReIV)-Re-4 cluster, giving a (Co3CoReIII)-Co-II-Re-III species. Spectroelectrochemical method; and irradiation experiments are used to characterize the metal-metal charge-transfer bands of this compound. A rhenium-based thermally induced one-electron reduction is observed for the (Cu4ReIV)-Re-II cluster to give a (Cu4ReIII)-Re-II complex; however, this reduction may be forestalled at low temperature. Finally, magnetic measurements reveal intracluster ferromagnetic exchange coupling, strong uniaxial magnetic anisotropy, and slow magnetic relaxation in the (Ni4ReIV)-Re-II and Cu-4(II) Re-IV clusters.