Keizo Horiuchi

Crystal Structure of (NH 4) 3H(SO 4) 2 in Phase I

The crystal structure of triammonium hydrogen disulfate (NH4)3H(SO4)2 in phase I has been studied by single-crystal X-ray diffraction. The space group is assigned as trigonal R\overline3, and the structure parameters are determined. The difference in the structural changes of (NH4)3H(SO4)2 and (NH4)3H(SeO4)2 at the ferroelastic-superionic phase transition is discussed.

Chlorine nuclear quadrupole resonances and motion of pyridinium ions in pyridinium tetrachloroaurate(III)

Abstract The temperature dependences of 35Cl NQR frequencies and of chlorine nuclear quadrupole relaxation times, T1Q have been determined for pyridinium tetrachloroaurate(III). The 35Cl NQR frequency of a single line appearing is 27.769 MHz at 293 K. With decreasing temperature, the NQR line is observed to become gradually broad and cannot be detected below ca. 230 K. 35Cl T1Q is observed to decrease with decreasing temperature from 800 μs at 350 K to 170 μs at 273 K. This fast relaxation rate may be responsible for the disappearance of the NQR signal described above. T1Q data are discussed by referring to the 1H NMR T1 data already determined. The dominant relaxation mechanism for T1Q below ca. 350 K can be attributed to the fluctuation of the field gradient due to the motion of the pyridinium ions in the crystal. Above ca. 360 K, T1Q decreases rapidly with increasing temperature suggesting the onset of a motion of [AuCl4]− ions. The activation energy for the motion is estimated to be 67 kJ mol−1. When the Larmor frequency of 1H T1 measurements is near to the NQR frequencies, anomalous temperature dependences of 1H T1 are observed, suggesting the occurrence of dipolar—quadrupolar cross relaxation with chlorine nuclei.

Phase transitions and anionic dynamics of dimethylammonium hexachlorotellurate(IV) as studied by pulsed nuclear quadrupole resonance of chlorine

Abstract The temperature dependence of 35 Cl NQR frequencies has been reinvestigated for dimethylammonium hexachlorotellurate(IV) using an FT NQR spectrometer. A new line is observed just above the lowest-frequency line already reported for the intermediate-temperature phase. In the lowest-temperature phase, the temperature dependence is definitely determined by finding new lines. The NQR frequencies can be precisely measured even in the vicinity of the phase transitions. The temperature dependence of the nuclear quadrupole relaxation time, T 1Q of 35 Cl and 37 Cl nuclei has also been observed. In a temperature range 64–160 K, the isotope ratio, T 1Q ( 37 Cl)/ T 1Q ( 35 Cl) is 1.5 for each line, suggesting that the quadrupolar relaxation arises mainly from the libration of the complex anion. Above 160 K, T 1Q decreases very rapidly with increasing temperature for each line. This can be interpreted in terms of the onset of the reorientation of the anion as a whole, which is responsible for the fade-out phenomenon of the two lines occurring near 220 K. The nature of the phase transitions and the anionic dynamics are discussed in detail. Especially, the phase transition at 96 K which is rather unusual and is explained through softening of the librations and the rotational displacement of the anions successively operated.

A 35Cl NQR Study on Exchange Interactions between Paramagnetic [IrCl6]2– Ions

The 35Cl and 37Cl NQR frequencies and spin-lattice relaxation times T1Q in paramagnetic M2IrCl6 (M = NH4, Cs) were measured at 4 - 350 K. The observed temperature dependences were attributed to EFG fluctuations caused by lattice vibrations and magnetic field fluctuations caused by paramagnetic ions. The exchange parameters in the NH4 and Cs salts were calculated from 35Cl NQR T1Q to be 8.6 K and 1.8 K respectively. 37Cl data yielded 9.1 K and 2.1 K respectively. The obtained lattice constant dependence of J values was explained by considering Ir-Cl Cl-Ir superexchange interaction

35Cl NQR, 1H NMR, and X-Ray Diffraction Studies in a Hydrogen Bonded Complex Na2PtCl6 · 6H2O

Abstract The 35Cl NQR frequencies, spin-lattice relaxation time and 1H NMR relaxation time were measured on crystalline Na2PtCl6 • 6H2O at 77-350 K. The presence of three nonequivalent chlorine sites found by X-ray diffraction measurement is in agreement with the observed three NQR lines, which have different temperature dependences attributable to differences in the direction of H-bonding with water molecules. The three NQR lines correspond to three kinds of chlorines with different Pt-Cl distances and H-bond directions.

Lattice stability in A2MCl6 ionic crystals (A identical to C5H5NH or CH3C5H4NH; M identical to Sn or Te)

DSC and NQR measurements were carried out for (CH3C5H4NH)2SnCl6 and (CH3C5H4NH)2TeCl6. No structural phase transition was observed above 85 K and 130 K up to the melting points for the Sn and Te compounds, respectively. Many A21MCl6 ionic crystals, where (MCl6)2- is an octahedral anion such as (SnCl6)2- or (TeCl6)2-, exhibit structural phase transitions accompanied by rotations of the MCl6 octahedra. However, (C5H5NH)2SnCl6 and (C5H5NH)2TeCl6 have been reported not to show such a displacive phase transition between 77 K and the decomposition temperature, although they undergo phase transitions driven by ordering of the pyridinium cations C5H5NH+. The stable lattices in these four compounds are discussed and explained qualitatively in terms of N-H...Cl hydrogen-bonding networks and a large primitive-cell volume.

NQR, DSC, and X-Ray Structure Studies of Pyridinium Tetrabromozincate and Pyridinium Tetrabromocadmate (C5H5NH)2MBr4 · nH2O (M = Zn and Cd; n = 0, 1); Phase Transitions and Weak Hydrogen Bond Interactions

Crystals of pyridinium tetrabromozincate and pyridinium tetrabromocadmate were obtained as monohydrates and anhydrous compounds. The crystal structure of metastable (C5H5NH)2- CdBr4・H2O was determined at 300(2) K; triclinic space group P1̄ with a = 7.875(2), b = 8.151(1), and c = 16.356(2) Å, α = 79.260(10), β = 86.030(10), and γ = 61.440(10)°, Z = 2. All compounds except for stable (C5H5NH)2CdBr4・H2O gave four 81Br NQR lines at temperatures between 77 and around 325 K. The stable (C5H5NH)2CdBr4・H2O undergoes a first-order phase transition at TC = 116 K. Four 81Br NQR lines below TC merged into two with equal intensities above TC, indicating a 180° flip motion of water molecules in the r. t. phase. The 81Br NQR lines of the two anhydrous compounds faded out around 325 K probably due to the reorientational motion of ZnBr42− or CdBr42− ions. The respective two 81Br NQR lines of the hydrates exhibited anomalous positive temperature dependence. This is considered to be induced by a weakening in the interionic C-H・ ・ ・Br hydrogen bonds with increasing temperature. The DSC measurements of the anhydrous compounds have revealed phase transitions above r. t. The thermal behavior of (C5H5NH)2CdBr4 is complicated by the formation of metastable forms. Graphical Abstract NQR, DSC, and X-Ray Structure Studies of Pyridinium Tetrabromozincate and Pyridinium Tetrabromocadmate (C5H5NH)2MBr4 · nH2O (M = Zn and Cd; n = 0, 1); Phase Transitions and Weak Hydrogen Bond Interactions

1H NMR Studies on the Cation Motions in Crystalline Cadmium Bromide Complexes [C(NH2)3]Cd2Br5, [(CH3)3NH]3Cd2Br7, and [i-C3H7NH3]CdBr3

1H NMR T1 measurements of crystalline [C(NH2)3]Cd2Br5 showed a single minimum due to the C3 reorientation of the planar [C(NH2)3]+ ion with an activation energy (Ea) of 35.8 kJ mol−1. In [(CH3)3NH]3Cd2Br7 crystals, two T1 minima appeared which are assigned to the C3 reorientation of methyl groups in the [(CH3)3NH]+ cation with Ea = 13.0 kJ mol−1 and to the C3 reorientation of a whole cation around the molecular C3 axis with Ea = 28.9 kJ mol−1. In [i-C3H7NH3]CdBr3 crystals, a very broad T1 minimum appeared near 160 K which is assigned to the C3 reorientations of two methyl groups with Ea = 11.3 kJ mol−1 and of an NH3 group with Ea = 13.3 kJ mol−1 in the [i-C3H7NH3]+ ion, and another minimum with Ea = 23.5 kJ mol−1 near 300 K assigned to a higher order molecular motion of the cation. Graphical Abstract 1H NMR Studies on the Cation Motions in Crystalline Cadmium Bromide Complexes [C(NH2)3]Cd2Br5, [(CH3)3NH]3Cd2Br7, and [i-C3H7NH3]CdBr3

Crystal structures of piperazinium tetrabromocadmate(II)-monohydrate [C4H12N2]CdBr4.H2O, piperazinium tetraiodocadmate(II) [C4H12N2]CdI4, and bis(trimethylsulphonium) tetrabromocadmate(II) [(CH3)3S]2CdBr4

Piperazinium tetrabromocadmate(II)-monohydrate, [C4H12N2]CdBr4 · H2O (1) crystallizes with isolated [CdBr4]2- anions, piperazinium cations, and water molecules (monoclinic, P21/c, Z = 4, a = 698.7(1), b = 1348.6(3), and c = 1432.4(3) pm, β = 92.97(3)˚ at 293 K). The crystal structure of 1 is almost the same as that reported in Inorg. Chim. Acta 187, 141 (1991). The crystal of piperazinium tetraiodocadmate(II), [C4H14N2]CdI4 (2) consists of isolated [CdI4]2- anions and piperazinium cations (orthorhombic,P212121, Z=4, a = 903.2(5), b = 1226.3(6), and c = 1307.9(7) pm at 293 K). The room temperature phase of bis(trimethylsulphonium) tetrabromocadmate( II), [(CH3)3S]2CdBr4 (3) has isolated [CdBr4]2- anions and trimethylsulphonium cations (orthorhombic, P212121, Z = 4, a = 911.3(1), b = 1329.2(2), and c = 1454.7(2) pm at 293 K).

NQR and DSC studies on structural phase transitions and lattice stability in some tetrabromozincate(II) compounds A2ZnBr4

The temperature dependence of 81Br NQR frequencies in some tetrabromozincate(II) compounds, pyridinium tetrabromozincate(II) (pyH)2ZnBr4, 4-picolinium tetrabromozincate(II) (4- piH)2ZnBr4, 2,6-lutidinium tetrabromozincate(II) (2,6-luH)2ZnBr4 and guanidinium tetrabromozincate( II) (guH)2ZnBr4,weremeasured between 77Kand temperatureswhere signals faded out.All compounds exhibited four NQR signals over the whole temperature range investigated. Moreover, DSC was measured between about 130 K and melting points. (4-piH)2ZnBr4 and (guH)2ZnBr4 showed no structural phase transition, while (pyH)2ZnBr4 and (2,6-luH)2ZnBr4 showed a single phase transition. The values of transition entropies obtained suggest that these transitions are of the order-disorder type. The nature of these transitions and the lattice stability in the present compounds were discussed