Hideta Ishihara

Hydrogen transfer in hydrogen-bonded chloranilic acid studied by 35Cl NQR I – a 1:2 complex with 1,4-diazine

Abstract 35 Cl NQR frequencies and spin-lattice relaxation time ( T 1Q ) and 1 H NMR relaxation times ( T 1H ) in a H-bonded three molecular system, chloranilic acid–1,4-diazine (1:2) were measured to reveal H-motions in a symmetric two H-bonds in solid. A single 35 Cl NQR frequency observed implies that the time-averaged structure of chloranilic acid is roughly monovalent in accordance with p K a values in both acid and base. T 1H temperature dependence was explained by a single relaxation mechanism due to the correlated H-transfer in two H-bonds, while that of T 1Q yielded two relaxation processes. One of these undetected by 1 H NMR was explained by the uncorrelated H-transfer.

NQR and X-ray Studies of [N(CH3)4]3M2X9 and (CH3NH3)3M2X9 (M = Sb,Bi; X = Cl,Br)

Abstract 35Cl, 81Br, 121Sb, and 209Bi NQR of the title compounds was observed. According to the results of the temperature dependences of NQR frequencies and the DTA measurements, phase transitions take place in [N(CH3)4]3Bi2Br9 (Ttr=183K), [N(CH3)4]3Bi2Cl9 (Ttr = 155K), and (CH3NH3)3Bi2Cl3 (Ttr = 200 and 249 K). 2D NMR spectra for partially deuterated (CH3ND3)3Bi,Br9 showed that the phase transitions in this compound are related to the motion of the methylammonium cations. Single-crystal X-ray work at room temperature shows that the space group for [N(CH3)4]3Sb2Cl9 is P63/mmc with a = 925.1 pm, c = 2173.4 pm, Z = 2. For (CH3NH3 ) 3Sb2Br9 the space group is P3ml with a = 818.8 pm, c = 992.7 pm, Z = 1; in both cases the cations show dynamical disorder. The Rietveld analysis of the powder X-ray diffraction for (CH3NH3)3Bi2Br9 reveals the space group P3ml with a = 821.0, c - 1000.4 pm, Z = 1 at room temperature; the compound is isomorphous with (CH3NH3 )3Sb2Br9 . The crystal symmetries of the low-temperature phases of (CH3NH3)3Bi2Br9 and [N(CH3)4]3Bi2Br9 were deduced from the results of the NQR spectroscopy

Guanidinium tetra-bromidomercurate(II).

The Hg atoms in the crystal structure of the title compound, (CH6N3)2[HgBr4], are tetrahedrally coordinated by four Br atoms and the resulting [HgBr4]2− tetrahedral ions are linked to the [C(NH2)3]+ ions by bromine–hydrogen bonds, forming a three-dimensional network. In the structure, the anions are located on special positions. The two different Hg⋯Br distances of 2.664 (1) and 2.559 (1) Å observed in the tetrabromidomercurate unit are due to the connection of Br atoms to different number of H atoms.

Bromine NQR and Crystal Structures of Tetraanilinium Decabromotricadmate and 4-Methylpyridinium Tribromocadmate

Abstract The 79,81Br NQR spectra of tetraanilinium decabromotricadmate (1) and 4-methylpyridinium tribromocadmate (2 ) were studied as function of temperature and their crystal structures were determined. (C6H5NH3)4Cd3Br10 (1): Space group D1 52h - Pbca , Z = 4, a = 2507.8(7) pm, b = 1985.4(5)pm, c = 763.0(2)pm. Characteristic for the structure are trioctahedral units [Cd3Br10] condensed to planes. Within the units the octahedra are face connected and further condensed to planes via common corners. Two types of hydrogen bonds are observed. The 81Br NQR lines with frequencies (MHz, 298 K) of 62.98, 52.59, 43.39, 41.82, and 40.71 are little temperature dependent with positive and negative coefficients. The wide frequency range of the NQR lines is reflected by the wide range of the intraionic distances, 263 ≤ d(Br-Cd)/pm ≤300. (4-(CH3)C5H4NH)CdBr3 (2): C52h - P21/n, Z = 4, a = 1228.8(5}pm, b= 1168.5(5)pm, c = 758.3(3)pm, β = 95.30(1)°; the CdBr⊖3 ions are condensed to chains. The 81Br NQR spectrum is a triplet with frequencies (MHz, 298 K) of 66.01, 55.39, and 50.75. The temperature dependence is small, with positive and negative temperature coefficients. The distances d(Cd-Br) are 256 pm (Cd-Br(2)), 261 pm (Cd -Br(1)), and 284 pm (Cd-Br(3)) and in the chain [CdBr3]Br(1) and Br(3) are bridging atoms. The relations between Br-NQR and crystal structures are discussed.

NQR study of [(CH3)2NH2]3InBr6 and [4-ClC5H4NH]2InBr5(H2O)

Abstract 81 Br, 115 In, and 35 Cl NQR spectra of dimethylammonium hexabromoindate(III)( 1 ) and 4-chloropyridinium pentabromoindate(III) monohydrate ( 2 ) were studied as a function of temperature. The 81 Br NQR spectrum of 1 is a quartet with frequencies (MHz, 298K) 55.93, 71.90, 72.04 and 78.26, and an intensity ratio of 2:1:1:2. For 2 , five 81 Br NQR lines were found with frequencies (MHz, 298K) 74.09, 76.12, 84.52, 93.04 and 94.04. The intensities are equal. The 35 Cl NQR spectrum of 2 is a doublet with frequencies (MHz, 298K) 35.50 and 35.72. The structure of the anions is deduced on the basis of the NQR results.

Differential scanning calorimetry studies on structural phase transitions and molecular motions in (CH3NH3)2MBr4 and [(CH3)2NH2]2MBr4 (M = Zn, Cd, and Hg)

Structural phase transitions and molecular motions in (CH3NH3)2MBr4 and in [(CH3)2NH2]2MBr4 (M = Zn, Cd, and Hg) were investigated by differential scanning calorimetry (DSC) between about 130 K and the melting points. All of the compounds showed at least one structural phase transition over the temperature region investigated. The values of the transition entropies obtained suggest that these transitions are of the order-disorder type. N-HBr hydrogen bonds were found to play an important role in the stability of P21/c room-temperature phases of the title compounds. In the highest-temperature solid phases of all title compounds, orientational orders of cations seem to be completely lost.

NQR and X-ray crystal structure studies of cadmium halide complexes: [C(NH2)3]CdI3 and [4-ClC6H5NH3]3CdBr5

Abstract The crystal structures of [C(NH2)3]CdI3 (1) and [4-ClC6H5NH3]3CdBr5 (2) have been determined at 100 K: monoclinic, Cc, a = 828.75(3) pm, b = 1615.31(5) pm, c = 810.64(3) pm, and β = 106.5820(10)° for 1; monoclinic, P21/c, a = 1486.93(5) pm, b = 794.31(3) pm, c = 2290.59(7) pm, and β = 99.6830(10)° for 2. The structure of 1 has an infinite chain of anions consisting of [CdI4] tetrahedra sharing two corners. The structure of 2 has an infinite chain of anions consisting of [CdBr6] octahedra sharing two corners in cis positions. In both structures, isolated cations are connected to the anion chains through weak hydrogen bonds Cd–X···H to result in three-dimensional network structures. In accordance with the crystal structures, three 127I (m = ±1/2 ↔ m = ±3/2), five 81Br, and three 35Cl nuclear quadrupole resonance (NQR) lines were observed for 1 and 2. The NQR spectra reflect the anion chain structures and their weak hydrogen bonds. The MO calculations of the models [Cd5I16]6– for 1 and [Cd3Br16]10– for 2 estimate only about half the values for the NQR frequencies but give accurate electric field gradient directions.

Bis(guanidinium) tetra­iodidomercurate(II)

The Hg atom in the crystal structure of the title compound, (CH6N3)2[HgI4], is tetrahedrally coordinated by four I atoms. The [HgI4]2− ions are interconnected to the [C(NH2)3]+ ions by N—H⋯I hydrogen bonds, forming a three-dimensional network. The four different observed Hg—I distances [2.760 (2), 2.7762 (15), 2.8098 (14) and 2.833 (2) Å] are consistent with four different 127I NQR frequencies observed, showing the existence of four unique I atoms in the tetraiodidomercurate unit.

NQR Study of AlBr3 Complexes with Donor-Acceptor O-Al Bond

Abstract 81Br and 27Al NQR were observed in AlBr 3 complexes with 4-XC6H4 NO,(X = H, CI, Br, I, CH3 , and C2H5), C6H5COBr, (C6H5)2CO, and (C2H5)2O. In the 4-XC6H4 NO2 complexes, the 27Al quadrupole coupling constants (QCCs) were well correlated with the Hammett er p s of the para-substituents, i.e., electron-withdrawing groups caused reduction of the charge density of O-Al bonds which resulted in large 27Al QCCs and vice versa. The temperature dependences of the 81Br NQR frequencies and quadrupolar spin-lattice relaxation times showed that the 4-C2H5C6H4NO2 and C6H5 COBr complexes undergo phase transitions at 154 K and around 200 K, respectively, and show hindered rotation of the AlBr3 groups at higher temperatures, and that the (C2H5) 2O complex reorients above ca. 120 K.

Structural change in (C5H5NH)SbBr4 with temperature

81 Br N.q.r. spectroscopy has revealed a drastic structural change in the (C5H5NH)SbBr4 crystal; above 253 K the SbBr4– anion has the trigonal bipyramid structure, whereas below 253K the axial bonds become asymmetric and the SbBr4– anion is more reasonably described as SbBr3·Br– at 77 K.