Calorimetric and Magnetic Studies of Crystalline and Glassy Bis[N-(3-methoxysalicylidene)isopropylamine]nickel(II)

Abstract

Abstract Thermal and magnetic properties of Ni(3-CH3O-SAL·iso-C3H7)2 were investigated by measuring thermograms, infrared and electronic spectra, heats of solution, magneitc susceptibilities, and heat capacities around glass transition temperature. In addition to the known paramagnetic crystalline phase III and the diamagnetic crystalline phase IV, two new crystalline phases (I and II) were discovered. Phase I was found to be paramagnetic, its molecular geometry being of a tetrahedral four-coordinated form like that of phase III, while phase II, similar to phase IV, is diamagnetic and has a square-planar four-coordinated form. Although the order of thermodynamic stability of these four crystalline phases was not determined, they were isolated stably at room temperature. The supercooled liquid and glassy states of this compound were realized for the first time by quenching the sample in the molten state. Unusual magnetic behaviors of these two states were satisfactorily accounted for by assuming an equilibrium between the diamagnetic and the paramagnetic species. In the supercooled liquid state, the paramagnetic species was partially converted into the diamagnetic one with decreasing temperature. Below the glass transition temperature Tg, however, this conversion process was prevented and the magnetic susceptibility obeyed apparently Curie’s law with a 26% paramagnetic content. The heat capacity measurement revealed a typical glass transition phenomenon at 297.5 K and the heat capacity jump at Tg was determined to be 172 JK−1mol−1. Detailed discussions were given for the relationship between molecular geometry and its associated magnetic property and also for the phase relationship between various phases.