Solvatomorphism-Induced 45 K Hysteresis Width in a Spin-Crossover Mononuclear Compound.

Spin-transition compounds are coordination complexes that can present two stable or metastable high-spin and low-spin states at a given temperature (thermal hysteresis). The width of the thermal hysteresis (difference between the maximum and minimum temperature between which the compound exhibits bi-stability) depends on the interactions between the coordination complexes within the compound, and which may be modulated by the absence or presence of solvent within the structure. The new compound [Fe(3-bpp)2 ][Au(CN)2 ]2 (1, 3-bpp=2,6-di-(1H-pyrazol-3-yl)pyridine) was synthesized and its properties were compared with those of the solvated compound [Fe(3-bpp)2 ][Au(CN)2 ]2 ⋅2 H2 O (1.H2 O) already described. 1 has a two-steps thermal hysteresis of 45 K, in contrast to the compound 1.H2 O which exhibits a gradual conversion without hysteresis. This hysteretic transition is accompanied by a reversible reconstructive structural transition and twinning. This stepped behaviour is also observed in the photomagnetic properties despite the low efficiency of photoswitching. Single-crystal photocrystallographic investigations confirm this low conversion, which we attributed to the high energy cost to form the high-spin structure, whose symmetry differs from that of the low-spin phase.

Photocatalytically-assisted electrooxidation of herbicide fenuron using a new bifunctional electrode PbO2/SnO2-Sb2O3/Ti//Ti/TiO2.

The degradation of the herbicide fenuron was investigated using a new porous bifunctional electrode where the electrooxidation takes place on one side and the photocatalysis on the other side. The characterization of the synthetized bifunctional electrode (PbO2/SnO2-Sb2O3/Ti//Ti/TiO2) was performed by scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction analysis and showed that the anodic side (Ti/SnO2-Sb2O3/PbO2) is covered with a tetragonal ß-PbO2 film and that the photocatalytic side (Ti/TiO2) consists of an anatase phase of TiO2. The single application of electrooxidation achieved 87.8% fenuron degradation and 84.1% chemical oxygen demand (COD) removal while heterogeneous photocatalysis resulted in only 59.2% and 39.7% fenuron concentration decay and COD removal, respectively. On the other hand, the photocatalytically-assisted electrooxidation (photo-electrooxidation) performed on the bifunctional electrode provided higher performances of fenuron degradation (97.5%) and mineralization (97.4%). Investigation of operating parameters highlighted the positive effect of increase in current density. Conversely, an increase in fenuron concentration led to a decrease in degradation rate and COD removal. It was also found that the COD removal and mineralization efficiency are higher in a neutral medium.