Thermodynamic, Physical, and Structural Characteristics in Layered Hybrid Type (C2H5NH3)2MCl4 (M = 59Co, 63Cu, 65Zn, and 113Cd) Crystals

Abstract

The thermal, physical, and molecular dynamics of layered hybrid type (C 2 H 5 NH 3 ) 2 MCl 4 (M = 59 Co, 63 Cu, 65 Zn, and 113 Cd) crystals were investigated by thermogravimetric analysis (TGA) and magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The temperatures of the onset of partial thermal decomposition were found to depend on the identity of M. In addition, the Bloembergen-Purcell-Pound curves for the 1 H spin-lattice relaxation time T 1ρ in the rotating frames of CH 3 CH 2 and NH 3 , and for the 13 C T 1ρ of CH 3 and CH 2 were shown to exhibit minima as a function of the inverse temperature. These results confirmed the rotational motion of 1 H and 13 C in the C 2 H 5 NH 3 cation. Finally, the T 1ρ values and activation energies E a obtained from the 1 H measurements for the H-Cl···M (M = Zn and Cd) bond in the absence of paramagnetic ions were larger than those obtained for the H-Cl···M (M = Co and Cu) bond in the presence of paramagnetic ions. Moreover, the E a value for 13 C, which is distant from the M ions, was found to decrease upon increasing the mass of the M ion, unlike in the case of the E a values for 1 H.Molecules 2020, 25, 1812 2 of 12 corner-sharing MCl 6 octahedra, while those of M = Co 2+ and Zn 2+ are simple MCl 4 tetrahedra [13]. In addition, the organic chains are joined by weak hydrogen bonds between the NH 3 groups and the Cl ions. Indeed, the structural geometries and molecular dynamics of the organic molecules within the layered hybrid structures are important for determining the influence of temperature on the structural phase transitions.As an example, (C 2 H 5 NH 3 ) 2 CoCl 4 crystallizes as an orthorhombic structure, which undergoes a reversible phase transition at 235 K [14]. In addition, (C 2 H 5 NH 3 ) 2 CuCl 4 undergoes phase transitions at 236, 330, 357, and 371 K [7,15-19], its crystal structure at room temperature is orthorhombic [20]. In contrast, (C 2 H 5 NH 3 ) 2 ZnCl 4 undergoes five phase transitions at 231, 234, 237, 247, and 312 K [21], crystallizing as an orthorhombic system at room temperature [22]. Finally, (C 2 H 5 NH 3 ) 2 CdCl 4 undergoes structural phase transitions at 114, 216, 358, and 470 K [9,23,24], whereby the room temperature orthorhombic phase has the Abma space group [23]. The structure of the organic component consists of a double layer of alkylammonium ions with the charged nitrogen atoms oriented to the nearest MCl 4 tetrahedra or MCl 6 octahedra. The phase transition temperatures, lattice constants, structures, and space groups for the four crystals are summarized in Table 1.