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

Abstract

The magnetic and photomagnetic properties of two cyano-bridged, [Mn(bpy)2]4[Mo(CN)8]2·14H2O (1) and [Mn(bpy)2]4[W(CN)8]2·9H2O (2) (bpy = 2,2‘-bipyridyl), hexanuclear clusters (hereafter named MnII4MIV2) have been investigated. Before irradiation both compounds behave as paramagnets in almost the whole temperature range due to the presence of magnetic MnII centers separated by the diamagnetic MIV 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 MnII, MnI, MIV, and MV centers. The formation of MnI and MV centers is interpreted in terms of the reductive quenching of the excited state through an intramolecular electron-transfer mechanism in the MnII4MIV2 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 MIV, MVI, and only MnII centers. The photochemical pathway in the presence of O2 is discussed in relation to the ligand-field photochemistry of octacyanometalates(IV), leading ultimately to the formation of [MVI(CN)4(O2)] and low-spin [MnII(bpy)2(CN)2] species in the solid state.