Magnetocaloric behaviour of liquid crystalline symmetric Co(II) and Ni (II) complexes of poly(propylene imine) dendrimers of the second generation

Two macromolecular complexes derived from poly(propylene imine) with Co(II) and Ni(II) ions have been synthesized by direct complexation between metal salts and the second generation dendrimers. Based on experimental data one can assume the formation of a binuclear complex in the case of Co2+ while the Ni2+ complex is characterized by the filling of all possible coordination sites. Magnetocaloric behaviour of symmetric Co(II) and Ni(II) complexes was found. It has been established that when the synthesized samples are exposed to a magnetic field, the sign of the specific amount of heat (QMCE) changes. Analyzing the obtained data on the magnetocaloric effect of the complexes, it was shown that the MCE values are changed from the negative value DT (Co(II)) =-0.016 K, DT (Ni(II)) =-0.005 K to positive DT (Co (II)) = 0.011 K, DT (Ni(II)) = 0.002 K (at T = 337 K and 1 T). The presence of a maximum in the temperature dependences of the heat capacity indicates a second-order phase transition. It was found for the studied complexes that they exhibit enantiotropic mesomorphism with the formation of columnar phases.& COPY; 2022 Elsevier B.V. All rights reserved.

Automated summary

Two macromolecular complexes derived from poly(propylene imine) with Co(II) and Ni(II) ions have been synthesized by direct complexation between metal salts and the second generation dendrimers. The Co2+ complex is assumed to form a binuclear complex, while the Ni2+ complex fills all possible coordination sites. The symmetric Co(II) and Ni(II) complexes exhibit magnetocaloric behavior and show a change in the sign of the specific heat (QMCE) when exposed to a magnetic field. The complexes also exhibit a second-order phase transition with a maximum value in the temperature dependence of the heat capacity, and show enantiotropic mesomorphism with the formation of columnar phases.