Heterospin Pressure Sensor

V. Ovcharenko
International Tomography Center,
Russian Federation

Keywords: spin transition, pressure sensor

Summary:

The reaction of copper hexafluoroacetylacetonate [Cu(hfac)2] with spirocyclic nitronyl nitroxide (L) gave a heterospin complex [Cu(hfac)2L], whose solid state is formed by polymer chains with a head-to-tail motif. The cooling of the compound to 110 K leads to a structural transition, as a result of which the unit cell volume decreases by more than 7%. The [Cu(hfac)2LEt] crystals are elastic and do not decompose during the thermally induced spin crossover. The transition from hightemperature to low-temperature phase is accompanied by a spin transition at 125 K, as a result of which [Cu(hfac)2L] transforms from a paramagnetic compound to a diamagnetic one due to the complete spin coupling in the Cu(II)–O•–N< exchange clusters inside the polymer chains. The reversible phase transformation is accompanied by a reversible contrastive change of color from blue to dark brown on cooling and vice versa from dark brown to blue on heating. The spin crossover temperature is very sensitive to the change of external pressure: when pressure increases from 1.0∙10-4 GPa to 0.48 GPa, it increases to 325 K. The increase of pressure provokes a transition from high-spin to low-spin state, which again transforms into the high-spin state when the external load is removed. Thus, the results of the study suggest that transition metal complexes with kinetically stable nitroxides are promising compounds that can serve as a basis for creating sensors expected to be highly sensitive to the external pressure.