Magnetocaloric behavior of REE porphyrin-based paramagnets at room temperature

REE complexes with cyclic aromatic ligands are ranked as the molecular materials with both electronic functionality and a single-molecule magnet behavior at temperatures lower 80 K. At the temperature close to room, they display a positive magnetocaloric effect (MCE) often comparable with one in ferromagnetics. We were determined MCE during the magnetization of both (5,10,15,20-tetra(4-tert-butylphenylporphinato))ytterbium(III)chloride, (Cl)YbT[Formula: see text]BuPP and (5,10,15,20-tetraphenylporphinato)ytterbium(III)chloride, (Cl)YbTPP in their aqueous suspensions over the temperature range of 278–320 K and in magnetic fields from zero to 1 T by the direct microcalorimetric method. Specific heat capacity in the solid of (Cl)YbT[Formula: see text]BuPP/(Cl)YbTPP has been directly determined in zero magnetic fields using differential scanning calorimetry. Thermodynamic parameters of ytterbium(III) complexes magnetization namely enthalpy/entropy change was determined. To improve understanding of the correlation between (Cl)YbT[Formula: see text]BuPP/(Cl)YbTPP magnetic properties and its electronic structure, we have compared magnetic behavior of paramagnets studied with those for (Cl)MTPP where M = Gd, Eu, Tm.

Magnetothermal properties of (octakis-trifluoromethylphenyltetraazaporphinato)manganese(III) acetate in aqueous suspension

The magnetocaloric effect (MCE), heat capacity, and magnetization thermodynamic parameters of the high-spin (octakis-trifluoromethylphenyltetraazaporphinato)manganese(III) acetate, (AcO)MnTAP(3-CF3C6H[Formula: see text], in a 1% aqueous suspension were determined by means of microcalorimetric method at 275–320 K in magnetic fields of 0.1–1.0 T. The conditions are comparable with those used with (octakis(3-tert-butylphenyl)tetraazaporphinato)manganese(III) acetate, (2,3,7,8,12,13,17,18-octaethylporphinato)manganese(III) chloride and (5,10,15,20-tetraphenylporphinato)manganese(III) chloride, acetate or bromide studied earlier. Paramagnetic properties were found in high-disperse particles of complexes, positive MCE values were obtained. As paramagnets, these complexes exhibit a big magnetocaloric effect (up to 0.85 K when the magnetic induction is changed from 0 to 1 T) at temperatures close to room, what could be employed for cooling in home and industrial refrigerators and hyperthermia in cancer diagnostics and therapy. MCE sensitivity to the nature and electronic structure of the aromatic macrocycle was discussed. The specific heat capacity of the complex depended on the temperature was obtained. Effect of magnetic field on the temperature dependence of the specific heat capacity for (AcO)MnTAP(3-CF3C6H[Formula: see text] practically is not visible.