Cationic motions and phase transitions in solid [(CH3)4N]2MX4 (M = Pd, X = Cl, Br; M = Pt, X = Br) complexes as studied by 1H NMR, differential thermal analysis, and X‐ray powder diffraction techniques

Abstract

AbstractThe temperature dependences of 1H spin‐lattice relaxation time, T1, differential thermal analysis, DTA, and X‐ray powder diffraction at and above room temperature were observed for tetramethylammonium tetrachloropalladate(II), tetrabromopalladate(II), and tetrabromoplatinate(II). At room temperature, the three complexes form isomorphous tetragonal crystals. Unusual solid‐solid phase transitions which were sensitive to moisture were found for the two tetrabromo complexes above room temperature. X‐ray powder patterns taken at various temperatures above room temperature for both complexes disclosed that the crystal structure determined for the samples once heated above transition temperatures was different from the above one determined at room temperature prior to the heating treatment. For the tetrachloro complex, 1H T1 curve observed is similar to the normal BPP curve except for a shoulder appearing on the hot side. Each tetrabromo complex yielded three different kinds of stable phases, i.e., the room, intermediate, and high temperature phases and additionally the supercooled metastable states of the latter two phases. The existence of two crystallographically nonequivalent cations is suggested for both bromo complexes in each intermediate metastable state. From the analysis of 1H T1 data obtained, motional parameters were determined for the cation in the crystals.