The magnetothermal properties of substituted (tetraazoporphynato)manganese(III) in aqueous suspension

Abstract

The magnetocaloric effect (MCE), heat capacity, and enthalpy and entropy of magnetization of the high spin (acetato) (2,3,7,8,12,13,17,18 octa para tert butylphenyltetraazaporphynato)manganese(III) complex in a 6% aqueous suspension were determined microcalorimetrically at 298 K in magnetic fields of 0.1-1.0 T, that is, under the conditions comparable with those used with (2,3,7,8,12,13,17,18 octaethylpor phynato)chloromagnanese(III) studied earlier. High dispersity complex particles were found to have para magnetic properties. Positive MCE values were obtained. These values grew as magnetic field induction increased. MCE sensitivity to the nature and electronic structure of the aromatic macroring was studied. The presence of aza groups in the structure of the complex decreases the MCE value compared with the porphyrin complex. The specific heat capacity of the complex strongly depended on the magnetic field value; field dependences had a maximum close to 0.3 T. Changes in the ΔS m (H, T) molar entropy part were also extremal and had maxima at 0.3-0.4 T. Prospects for the use of magnetothermal properties in the quantitative deter mination of thermodynamic characteristics and for revealing trends of changes in the magnetic activity of porphyrin complexes are discussed.

Recent progress in organometallic porphyrin‐based molecular materials for optical sensing, light conversion, and magnetic cooling

“…MCE related to the completely thermostatic calorimetric cell with solid paramagnets and water above it were observed in the first works. [167][168][169][170][171] A paramagnet heat capacity observed in the same experiment as for MCE values and calculated according to Equation (10 was evaluated as a difference (Equation (11). In the subsequent works, [34,166,[172][173][174][175][176][177] a new method based on using Equation (12 had allowed to eliminate the influence of a cell without a paramagnet and to determine the paramagnet true MCE.…”

“…In the first case, the MCE value depends not only from the spin state of a central ion but also from an electronic and chemical structure of bonded axial groups (Figure 13 created by using the works [166,167,[169][170][171][172][173]175,177,178] ), which ultimately leads to spin density delocalization or to ferromagnetic coupling with an additional spin carrier in a molecule structure. To give insight into the nature of spin distribution, they resort to comparative analysis of paramagnet UV-vis spectra or to computational calculations.…”