Photo- and dehydration-induced charge transfer processes accompanied with spin transition on CoFe(CN)(5)NH3 center dot 6H(2)O

The coexistence of different valences of iron and cobalt in cobalt pentacya noferrate, CoFe(CN)(5)NH3. 6H(2)O, was confirmed by the infrared spectrum, in which two distinct peaks for the C-N stretch at 2162 cm(-1) and 2117 cm( -1) were assigned to CN in Fe-III-CN-Co-II and Fe-III-CN-Co-III respectivel y, and by the Mossbauer spectrum, in which Fe-III and Fe-II exhibited doubl ets with different isomer shifts and different quadrupole splitting. Photo- irradiation of this compound with red light changed the population of these two electronic states due to the internal electron transfer from Fe-II to Co-III, As a result, the ferrimagnetic properties of this pentacyanometalat e at low temperature can be changed by photo-irradiation similar to the cas e of the hexa-cyanometalate, K0.2Co1.4Fe(CN)(6).6.9H(2)O reported previousl y (O, Sate ct al,, Science 272, 704 (1996)), Moreover, the fraction of thes e two electronic states in this pentacyanoferrate is sensitive to the numbe r of water molecules, which induces a charge transfer from Co-II and Fe-III , As a result, dehydration increases the fraction of Fe-II-CN-Co-III and ca uses the compound to be paramagnetic even at low temperature. (C) 2001 Acad emic Press.