Structural and photo-induced magnetic properties of MII 2[WIV(CN)8]·xH2O (M=Fe and x=8, Cu and x=5). Comparison with CuII 2[MoIV(CN)8]·7.5H2O

This article describes bimetallic extended networks built from WIV(CN)8 4− and M2+=FeII, CuII, denoted hereafter as FeW for FeII 2[WIV(CN)8]·8H2O and CuW for CuII 2[WIV(CN)8]·5H2O. The crystal structure was solved in the tetragonal system for M=Fe, and consists of a three-dimensional (3D) structure with alternating W(CN)8 and Fe(H2O)2 units leading to an architecture formed by two perpendicular grids. X-ray powder studies for M=CuII have revealed that the compound crystallizes in the orthorhombic system. In order to obtain structural information of the network, the compounds have also been investigated by the WAXS technique. The results proved that both compounds adopt a similar architecture. All these structural features are compared to those obtained previously for MII 2[MoIV(CN)8]·xH2O denoted as FeMo and CuMo for M=Fe and Cu, respectively. FeW and FeMo compounds show identical 3D networks, whereas powders of Cu compounds are different: CuW is well crystallized and CuMo is poorly crystallized. The magnetic properties of the W analogs revealed weak antiferromagnetic interactions through the diamagnetic spacer NCWIVCN. The photomagnetic studies at different wavelengths (λ=413 and 530 nm) were performed for the Cu compounds. No effect was observed for CuW, whereas a photo-induced magnetic ordering is obtained for CuMo, explained by a photo-induced electron transfer between the MoIV and CuII metal centers. These results are discussed in relation with the structural features of the compounds.