Photomagnetism in Cyano-Bridged Hexanuclear Clusters [Mn^II(bpy)₂]₄[M^IV(CN)₈]₂·xH₂O (M = Mo, x = 14, and M = W, x = 9)

The magnetic and photomagnetic properties of two cyano-bridged, [Mn(bpy) 2 ] 4 [Mo(CN) 8 ] 2 ·14H 2 O ( 1 ) and [Mn(bpy) 2 ] 4 [W(CN) 8 ] 2 ·9H 2 O ( 2 ) (bpy = 2,2‘-bipyridyl), hexanuclear clusters (hereafter named Mn II 4 M IV 2 ) have been investigated. Before irradiation both compounds behave as paramagnets in almost the whole temperature range due to the presence of magnetic Mn II centers separated by the diamagnetic M IV spacers in the molecules. After several hours of irradiation (337−356, 406−415, and 480 nm) in a superconducting quantum interference device at 10 K, the magnetic signal at 10 K has increased by a factor of almost 30% compared to that of the initial magnetic state. The magnetic characterization of the irradiated samples indicates the formation of a photoproduct exhibiting antiferromagnetic interactions. The X-ray photoelectron spectroscopy (XPS) data of the irradiated samples show the presence of Mn II, Mn I, M IV, and M V centers. The formation of Mn I and M V centers is interpreted in terms of the reductive quenching of the excited state through an intramolecular electron-transfer mechanism in the Mn II 4 M IV 2 clusters. After irradiation at room temperature in the presence of air, both compounds behave as a paramagnet, but with a lower magnetic response than that of the initial state. The XPS data show the presence of M IV, M VI, and only Mn II centers. The photochemical pathway in the presence of O 2 is discussed in relation to the ligand-field photochemistry of octacyanometalates(IV), leading ultimately to the formation of [M VI (CN) 4 (O 2 )] and low-spin [Mn II (bpy) 2 (CN) 2 ] species in the solid state.