Photo-induced magnetization in copper(II) octacyanomolybdate(IV)

The photomagnetic effect of the mixed-valence compound Cu-2(II)[Mo-IV(CN)(8)].7.6H(2)O (Cu-II; 3d(9), S = 1/2, Mo-IV; 4d(2) = 0) (1) was investigated. The UV-VIS spectra showed the intervalence transfer (IT) band between Mo-IV-CN-Cu-II and Mo-V-CN-Cu-I around 500 nm. When the paramagnetic compound 1 was irradiated by a filtered blue light (400-430 nm, 3 mW/cm(2)) of a Xe lamp at 5 K, the irradiated sample exhibited a spontaneous magnetization with a Curie temperature of 17 K. By annealing the irradiated sample above 200 K, the magnetic property of this sample returned to the initial state. This photo-induced magnetization is explained by the following mechanism. The excitation of the IT band causes the electron transfer from Mo-IV (S = 0) to Cu-II (S = 1/2), producing a mixed-valence isomer of Mov (S = 1/2)-CN-Cu-I (S = 0). However, half of the copper ions remain as Cu-II ions due to the stoichiometric limitation and hence the irradiated 1 is expressed as (CuCuII)-Cu-I[Mo-V(CN)(8)].7.6H(2)O. The unpaired electrons on Mov (S = 1/2) ions and those on Cu-II (S = -1/2) ions in the irradiated compound interact ferromagnetically, giving rise to the spontaneous magnetization. (C) 2001 Elsevier Science B.V. All rights reserved.