Physicochemical insight into the metal atom effect on magnetocaloric behavior of paramagnetic metalloporphyrins

Heat capacities, magnetization thermodynamic parameters, and magnetocaloric effect in cobalt(II), manganese(III), and molybdenum(III) complexes with porphyrins were studied using DSC, the direct microcalorimetric method, and the DFT approach. Contribution of spin density distribution between a central ion and ligands in positive MCE in paramagnets was quantitatively characterized. [Display omitted] To reveal the effect of coordinated organic and inorganic σπ-ligands on the magnetocaloric properties of metal ions at room temperature, we have synthesized paramagnetic (5,10,15,20-tetraphenylporphinato)cobalt(II), (chloro)(2,3,7,8,12,13,17,18-octaethylporphinato))manganese(III), their coordination complexes with 1-methyl-2-(pyridin-4′-yl)-3,4-fullero[60]pyrrolidine (1:3 and 1:2, respectively), and (ethoxy)(oxo)(5,10,15,20-tetraphenylporphinato)molybdenum(V) and have fully characterized their chemical structure by UV–vis, IR, 1H NMR, MALDI TOF spectral methods. Using the direct microcalorimetric method and DSC we have obtained, respectively, magnetocaloric effect, heat, change of enthalpy/entropy during the magnetization over the temperature range of 285 – 338 K in magnetic fields from zero to 1 T and the specific heat capacities in the temperature range from 270 to 400 К in zero fields for paramagnets synthesized. Involving the results of DFT calculations, we have shown that the electron structure of a central metal atom is the determining factor in the positive magnetocaloric effect in the complexes studied. The decrease in the MCE value is observed in the case of the intramolecular antiferromagnetic interactions in external magnetic fields (manganese(III) complexes) and additional axial bonding of the bulk fullerene-containing base.