Central atom/substituent effects onmagnetothermal properties of metal porphyrins in aqueous suspension

• Magnetothermal properties of Mn/Ln(III) porphyrins were obtained by microcalorimetry.
• (AcO)GdTPP shows giant magnetocaloric effect compared to La0.8Ag0.15MnO3.
• Mn porphyrins’ heat capacities depend on induction with a maximum at 0.25–0.35 T.
• Dependences of MCE on molecules structure were determined for the first time.
• We explored the prospects of using metal porphyrin magnetothermal properties for various applications.

Magnetothermal properties of (X)MnIIIP and (X)LnIIIP, where X = chloro-, bromo-, acetate-ligand; Ln = Eu, Gd, Tm and P = (2,3,7,8,12,13,17,18-octaethylporphyrinato)-, (5,10,15,20-tetraphenylporphyrinato)- or (2,3,7,8,12,13,17,18-octa-para-tert-butylphenyltetraazaporphyrinato)-ligand, as 6% water suspensions were determined by the microcalorimetric method at 298–353 K in a magnetic induction of 0–1.0 T. High-disperse complex particles were found to have paramagnetic properties. It was established that positive MCE increases with an increase in magnetic induction at all temperatures and decreases with an increase in temperature at all magnetic inductions; in the case of (Cl)GdTPP actually MCE does not depend on temperature. Dependences of specific heat capacity and that of the change in enthalpy and magnetic entropy of the studied complexes on magnetic induction were explored. The first of these dependencies has a maximum at 0.25–0.35 T at all temperatures. Heat capacity of the lanthanide complexes slightly increases with an increase in temperature; a magnetic component of heat capacity takes place only in (AcO)GdTPP at temperatures above 298 K. The regularities of the influence of central atom, acidoligand and a macrocycle composition in porphyrin complexes on their magnetothermal properties were established. Both a macrocycle composition in the case of manganese complexes and an acidoligand variation in the case of lanthanide complexes are bigger than the other studied factors. We explored prospects for the use of magnetothermal properties in the quantitative determination of thermodynamic characteristics and for revealing trends of changes in the magnetic activity of porphyrin complexes. It was shown that high magnetocaloric effect of (AcO)GdTPP compared with the lanthanum manganite doped by silver ions goes and gets a perspective for a wide range of potential industrial-scale applications in new refrigerating machinery and in a hyperthermia for a medicine.