Structural analysis of the incommensurate and lock-in phases of tetramethylammonium tetrachlorozincate(II), [N(CH₃)₄]₂[ZnCl₄]

Abstract

The structures of the incommensurate and lock-in phases of [N(CH3)4]2[ZnC14] have been determined and analysed in terms of symmetry modes. X-ray diffraction intensities of the incommensurate phase, including first-and second-order satellites, were collected at 286.4 K. Refinements were performed in the superspace group P(Pmcn):(s, 1, -1) including in the modulation function harmonics up to second order.0108-7681/87/040356-13501.50From a total of 475 independent reflections, final R values of 0.077, 0.052, 0.121 and 0.49 for all, main, first-and second-order reflections, respectively, were obtained. First-order harmonics dominate in the modulation, the most important component of the distortion being that parallel to the a axis. The refinements of the lock-in ferroelectric structure were performed in the space group P21 cn, using as starting parameters those of the basic structure extended to five cells. A final R = 0.075 for 917 observed reflec-

New Noncentrosymmetric Material - [N(CH3)4]ZnCl3: Polar Chains of Aligned ZnCl4 Tetrahedra

“…These bond distances and angles are consistent with those of previously reported zinc chlorides. [32][33][34][35][36][37][38][39][40][41][42][43][44] The two ZnCl 4 tetrahedra share their corners to form one-dimensional chains that run parallel to the a-axis (see Figure 2). Although there are slight deviations, interestingly, all the ZnCl 4 tetrahedra in the chains are approximately aligned in one direction (see Figure 3).…”

Manifestations of Phase Transitions and the Thermooptical-Memory Effect in the Absorption Spectra of (N(CH3)4)2CuCl4 Crystals

“…Undoubtedly, this phenomenon is due to the incommensurate modulation. By analogy with the isomorphic TMA-ZnCl 4 crystal [15], it may be suggested that the spatial modulation of the crystal studied is caused by the turns of the deformed [CuCl 4 ] 2− tetrahedrons around their three crystallographic axes. The value of these turns changes continuously within the incommensurate phase limits with change in the temperature and, in doing so, reproduces the continuous change in the incommensurate-modulation vector.…”

Molecular Motions of [N(C2H5)4]+and [N(CH3)4]+ions by1H Nuclear Magnetic Resonance Relaxation in [N(C2H5)4]2CoCl4and [N(CH3)4]2CoCl4Single Crystals

“…Co, 63 Cu, and 67 Zn) single crystals belong to the group of A 2 BX 4 -type crystals. [1][2][3][4][5] The magnetic resonance relaxation times of nuclear spin systems have been widely used to elucidate various types of atomic motions in crystals because these relaxation times are related to the structures and internal motions of solids; in particular, the protons of these solids act as resonant nuclei, so the relaxation times of these nuclei reflect the ionic motions in the solid. 1…”