81Br NQR Lines Research Articles

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 ZnBr4 2− or CdBr4 2− 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.

Secondary bonding and coordination of mercury in 5-nitrobenzimidazolium trihalogenomercurates(II) [C 7H 6N 3O 2]HgX 3·H 2O (X = Cl, Br, I): Synthesis, characterization by FT IR, NQR and single crystal X-ray diffractions

Three new mercury(II) halide complex salts, [C 7H 6N 3O 2] HgX 3·H 2O ( 1: X = Cl, 2: X = Br, 3: X = I) synthesized by reacting stoichiometric quantities of appropriate reactants in aqueous medium, have been investigated by FT IR, NQR spectroscopies, and single crystal X-ray diffractions. The crystal structures of 1 and 2 are isostructural with orthorhombic system (P nma); a = 15.943(5), b = 6.357(6), c = 12.733(7) Å, Z = 4 at 296(2) K for 1 and a = 16.104(4), b = 6.539(4), c = 13.059(4) Å, Z = 4 at 296(2) K for 2, respectively. In the crystal Structures, a planar cation of C 7 H 6 N 3 O 2 + , a planar trigonal anion of HgX 3 – [X = Cl, Br] and water molecule are arranged through the hydrogen bonds of X⋯H–O, O⋯H–N, and X⋯H–N into 2D sheets which are parallel to ac plane. The sheets are connected by double chains of Hg⋯X interionic bonds, which run along the b directions. In contrast, 3 crystallizes in monoclinic (P2 1/n) space group with a = 7.321(6), b = 16.205(5), c = 13.113(4) Å, β = 96.94(4)°, and Z = 4 at 298(2) K. The crystal structure of 3 consists of a pair of 5-nitrobenzimidazolium cations associated through hydrogen bonds with water molecules and a Hg 2 I 6 2 - dimer in which Hg atoms are tetrahedrally coordinated. In accordance with the crystal structures, three NQR lines due to 81Br and 127I( m = ± 1/2 ↔ ± 3/2) were observed at room temperature for 2 and 3, respectively, while two 35Cl NQR lines being assignable to the terminal Cl atoms were observed for 1. The splitting into two 81Br NQR lines of each line below around 160 K shows an occurrence of a phase transition followed by a slight structural change into a structure with lower crystal symmetry. A corresponding disappearance of 35Cl NQR lines below about 110 K may indicate an occurrence of a phase transition in 1. The effects of secondary bonding of interionic Hg⋯X and hydrogen bonds on the coordination of Hg atoms as well as the crystal structures have been discussed.

NQR Study of Phase Transition and Cationic Motion in 4-NH2C5H4NHBiBr4·H2O

Four 81Br NQR lines in 4-NH2C5H4NHBiBr4·H2O were observed in the temperature range between 77 and ca. 380 K; with increasing temperatures the respective sets of higher and lower two resonance lines coalesced into single lines discontinuously at 274 K, showing the occurrence of a first-order type phase transition of this crystal. The transition was confirmed with heat anomaly on a DTA curve. Each higher and lower line of high-temperature phase is assignable to the terminal Br atoms and the bridging ones of one-dimensional poly anions (BiBr4 −)n in the crystal structure (C2/c), which was investigated by a X-ray structure analysis at room temperature. The 1/T 1 temperature dependence of 81Br NQR follows the usual T 2 law in the temperature range between 77 and ca. 140 K, being explained by fluctuation of the EFG at Br nucleus due to lattice vibrations. The T1 vs. 1/T curve in the temperature range between about 160 and 190 K was describable by the exponential curves, allowing us the estimation of activation energies. These exponential behaviors of T 1 of 81Br NQR are attributable to the fluctuations caused by the thermal motion of 4-NH2C5H4H+ ions. Echo signals of the 81Br NQR could not be detected above 190 K owing to poor S/N with very short T 2.

NQR, NMR and Crystal Structure Studies of [C(NH2)3]2HgX4 (X = Br, I)

The crystal structure of [C(NH2)3]2HgBr4 has been determined at room temperature: monoclinic, space group C2/c, with a = 10.035(2), b = 11.164(2), c = 13.358(3) A, β = 111.67(3)°, and Z = 4. The crystal consists of planar [C(NH2)3]+ and distorted tetrahedral [HgBr4]2− ions. The Hg atom is located on a two-fold axis such that two sets of inequivalent Br atoms exist in an [HgBr4]2− ion. In accordance with the crystal structure, two 81Br NQR lines widely separated in frequency were observed between 77 and ca. 380 K. [C(NH2)3]2HgI4 yielded four 127I NQR lines ascribable to m = ±1/2 ↔ ±3/2 transitions, indicating that its crystal structure is different from the bromide complex. The 1H NMR T 1 measurements showed a single minimum for the bromide but two minima for the iodide. The analyses based on the C3 reorientations of the planar [C(NH2)3]+ ions gave the activation energies of 29.8 kJ mol−1 for the bromide, and 30.2 and 40.0 kJ mol−1 for the iodide.

81Br NQR and 1H NMR of Guanidinium Hexabromoantimonate(V) [C(NH2)3]SbBr6: Phase Transition and Molecular Motion

Guanidinium hexabromoantimonate(V) [C(NH2)3]SbBr6 was prepared. It was black in color at room temperature and showed a tendency to turn yellow by loosing bromine in open air. Six 81Br NQRlines were observed at 77K.On heating, four of the six lines faded out around 200 K,while the remaining two lines could be observed up to room temperature. This temperature behavior suggests a preferential libration or reorientation around a pseudo C4 axis of the octahedral [SbBr6]- anion. DTA measurement revealed a small heat anomaly at Tc1 = 273 K (on heating), showing a thermal hysteresis, and a sharp and large anomaly at Tc2 = 314 K. The temperature dependence curve of 1H NMR T1 is characterized by a single minimum of 26 ms (32 MHz) near 280 K, which is assigned to the C3 reorientation of the planar [C(NH2)3]+ cations. Its activation energy ( a) is 43.3 kJ/mol

Pseudo-symmetries of the Phases of (Et4N)2ZnBr4

Abstract The phase sequence of (Et4N)2ZnBr4 has been determined based on thermal analysis. Below the decomposition point (572 K) four phases are distinguished. The structures of three of the phases have been determined from 4-circle diffraction data at 240 (neu-trons), 299 and 373 K (X-rays), respectively. The multiply twinned low-temperature phase (at 240 K) is characterized by a pseudo-orthorhombic lattice (monoclinic, Plal, a = 17.6120(9] Å, b = 8.8195(4) Å, c = 16.1062(6) Å and ß=89.94(2)°), whereas the room-temperature phase (299 K:P421c, a = 8.9874(6)Åand c = 15.9774 Å) and the first high-temperature phase (373 K: P42 /nmc, a= 9.145(4) Å and c = 15.835(8) Å) belong to the tetragonal crystal system. The transitions between the three phases are essen-tially connected with a stepwise ordering of the Et4N+ ions, whereas the positions of the heavy atoms change only slightly. Three 81Br NQR lines are observed between 77 and 204 K.

Isolated versus Condensed Anion Structure VI: X-ray Structure Analysis and 81Br NQR of Guanidinium Pentabromodicadmate(II), [C(NH2)3]Cd2 Br5 , tris-Hydrazinium Pentabromocadmate(II), [H2NNH3]3 CdBr5 , and bis-Hydrazinium Tetrabromocadmate(II)-Tetra Hydrate, [H2NNH3]2CdBr4-4H20

The structure of the condensed bromocadmate anions in [C(NH2)3]Cd2Br5 (1) and [H2NNH3]3CdBr5 (2) were studied at room temperature by X-ray diffraction. (1) crystallizes with double-chains bridged by Br atoms (orthorhombic, Pmmn, Z= 2, a = 1394.0(5), b = 394.5(1), c = 1086.9(5) pm). This chain structure was not described previously. (1) shows three 81Br NQR lines at temperatures between 77 and 323 K. Structural phase transitions take place at 283 K and at 535 K. (2) crystallizes with Br bridged zigzag-chains (monoclinic, P21, Z=2,a = 943.1(1), b = 778.8(2), c = 942.0(2) pm, β = 102.10(2)°) and shows a first-order phase transition around 304 K with a large thermal hysteresis. Below the transition point five 81Br NQR lines are observed at temperatures between 122 and 304 K, and above the transition point four 81 Br NQR lines at tem-peratures between 288 and 353 K. Two 81Br NQR lines are observed in [H2NNH3]2CdBr4 -4H20 (3) at temperatures between 77 and around 320 K with positive temperature coefficients

Crystal Structure and Phase Transition of 4-Aminopyridinium Tetrabromoantimonate(III) as Studied by Bromine and Antimony NQR, Proton NMR, and Single Crystal X-Ray Diffraction

The crystal structure of the room temperature phase (RTP) of the title compound was determined at 297 K (monoclinic, space group C2/c, a = 1384.2(2), b = 1377.8(3), c = 755.5(2) pm, β = 121.58(1)°). A complicated disorder was found for the cation. A phase transition from the low-temperature phase (LTP) to the RTP was found at (224 ±1) K (Tc). The 1H NMR spectra showed a sharp motional narrowing at ca. T=Tc , indicating the occurrence of a reorientational motion of the cation in the RTP in accord with the disorder. It was found that another reorientational motion is excited in the LTP. Four 81Br NQR lines (132.71, 115.38, 61.54 and 59.31 MHz at 77 K) and two Sb NQR lines (53.78 and 33.76 MHz at 77 K) were found in the LTP, while a single 81Br NQR line was observed at T> 276 K (ca. 121.80 MHz at 300 K). Crystal dynamics are discussed on the basis of the temperature dependence of the NQR, 1H NMR line width, and 1H NMR T1.

Isolated versus Condensed Anion Structure V: X-ray Structure Analysis and 81Br NQR of t-butylammonium tribromocadmate(II)-1/2 water, i-propylammonium tribromocadmate(II), and tris-trimethylammonium heptabromodicadmate(II)

The crystal structures of the condensed bromocadmate anions with chains built of [CdBr3]∞ were de-termined by X-ray structure analysis at 300 K. In addition, the temperature dependence of the 81Br NQR frequencies was observed. [(t-C4H9NH3)CdBr3]2-H2O (1) tallizes with a double Br bridged chain (monoclinic, P2/c, Z = 4, a = 1963.4(8), b 87.7(4), c 1432.1(6) pm, and ß= 110.66(2)°). Six 81Br NQR lines are observed at temperatures between 77 and 330 K. (i-C3H7NH-3)CdBr3 (2) crystalliz-es with a triple Br bridged chain (orthrhombic, Pbca, Z= 8, a = 1975.4(6), b = 1415.8(4), c = 690.1(2) pm). (2) shows three 81Br NQR lines at temperatures between 77 and 193 K. A phase transition occurs at 224 K. The structure of [(CH3)3 NH]3Cd2Br7] (3) was redetermined. (3) consists of a triple Br bridged chain and a discrete [CdBr4] tetrahedron (hexagonal, P63mc, Z= 8, a = 1483.5(2), c = 685.7(5) pm). The structure of (3) is identical to the one reported by Daoud, Perret, and Dusausoy, Acta Crystallogr., B35, 2718 (1979). Three 81Br NQR lines are observed at temperatures between 77 and 243 K.

Isolated versus Condensed Anion Structure IV: An NQR Study and X-ray Structure Analysis of [H3N(CH2)3NH3]CdI4 * 2H2O, [H3CNH2(CH2)3NH3]CdBr4, [(CH3)4N]2CdBr 4, and [(CH3)3S]2CdBr4*

Abstract The phase I of [H3N(CH2)3NH3]CdI4 • 2H2O (1) crystallizes with isolated [CdI4]2-tetrahedra; monoclinic, C2/c, Z = 8, a = 1702.6(3), b= 1459.3(3), c= 1555.5(3) pm, and ß= 120.32(3)° at 299 K. (1) shows a first-order phase transition at T1↔II = 245 K. The eight 127I(v1) NQR lines in phase II change discontinuously into four lines in phase I. The transition entropy from DSC measurements, ∆S = 5.0 J K1- mol-1 , shows that this transition is probably due to order-disorder of cations. [H3CNH2(CH2)3NH3]CdBr4 (2) crystallizes with isolated [CdBr4]2- tetrahedra; orthorhombic P212121, Z = 4,a= 1447.8(5), b = 1280.3 (4), c = 709.7(3) pm at 299 K. (2) shows four 81Br NQR lines between II and around 325 K, above which temperature the lines disappear. [(CH3)4N]2CdBr4 (3) shows a second-order phase transition at T1↔II = 271 K. Three of four 81Br NQR lines in phase II disappear below this transition point, the other line can be observed up to 315 K. The transition entropy, ∆S = 9.01 J KT-1 mol-1 , indicates that the transition is an order-disorder type of the cations. [(CH3)3S]2CdBr4 (4) shows a first-order type phase transition at T1↔II = 304 K. The four lines spectrum of 81Br NQR is observed in phase II and disappears above the transition point. The transition entropy, ∆S = 46.8 J K- 1 mol-1 is abnormally large. The role of the hydrogen bond and the bridging power between the halogen and cadmium atoms upon the formation of the condensed anion structure is discussed.

Phase Transitions and Crystal Structure of Dimethylammonium Tribromomercurate(II), (CH3)2NH2HgBr3 , as Studied by 81Br NQR and Single Crystal X-ray Diffraction

Abstract The temperature dependence of the 81Br NQR frequencies of the title compound has revealed the presence of three phases (I, II and III, in the order of decreasing temperature): Tcl (II -1) = (318 ± 10) K and Tc2 (III -II) = (202 ± 1) K. The transitions were confirmed by thermal analysis (DTA). Both of the II-I and I-II transitions exhibited strong hysteresis (i. e., superheating and supercooling, respectively). The crystal data, determined by single crystal X-ray diffraction, are: monoclinic, space group P2/a, a = 1384.8(3), b = 934.7(4), c = 1452.0(2) pm, β = 104.10(1)°, Z= 8, R = 0.076. The crystal has two crystallographically independent cations (CH3)2NH2+ and an infinite chain of anions almost in the c-direction. The anion chain is considered to consist of a HgBr2 molecule and two different HgBr4 2- anions which are interconnected via weak intermolecular Hg···Br bonds. The splitting patterns of the 81Br NQR spectra indicate that rearrangements of the Hg-Br bonds are slight at the III-II transition but serious at the II-I transition. Some of the 81Br NQR lines show anomalous temperature coefficients, attributable probably to thermal motions of cations.

Isolated versus Condensed Anion Structure II; the Influence of the Cations (1,3-propanediammonium, 1,4-phenylendiammonium, and n-propylammonium) on Structures and Phase Transitions of CdBr2- 4Salts A 79,81Br NQR and X-ray Structure Analysis

Abstract The influence of the cations on the condensation of anions CdBr4 2- in salts (A')CdBr4 (II) and (A)2CdBr4 (II) is studied by 79,81Br NQR and X-ray crystal structure determinations. (A')CdBr4 : A' = [H3N(CH2)3NH3]2+ (1) crystallizes with a layer-type anion structure at 298 K and A' = [1,4-(H3N)2C6H4]2+ (2) crystallizes with a chain-type anion structure at 298 K. (A)2 CdBr4 : A = [n-H3C(CH2)2NH3]+ (3) crystallizes with a layer-type anion structure at 293 K. (1) shows successive phase transitions at 328, 363, and 495 K according to the NQR and DSC measurements. Phase IV of (1): at 298 K orthorhombic, Pnma, Z = 4,a = 772.1 (4), b = 1905.4(9), c = 789.8(4) pm. 81Br NQR spectrum showed a doublet at 77 K (phase IV) with ν1= 61.177 and ν2 = 45.934 MHz and also a doublet at 350 K (phase III) with ν1= 57.581 and ν2 = 48.747 MHz. (2): at 295 K orthorhombic, Pnma, Z = 4, a = 802.5(3), b = 1775.1(6), c = 881.9(3) pm; the five-coordinated Cd atom and one-dimensional [CdBr4]2- anion chain structure was observed. This coordination and chain structure are very rare for (A')CdX4 (II) or (A)2CdX4 (II). Two 81Br NQR lines were observed at 77 K: ν1= 70.159 and ν3 = 40.056 MHz. One more line appeared at 85 K: ν2 = 53.622 MHz. A 81Br NQR triplet was observed at 273 K: ν1 = 67.919, ν2 = 56.317, and ν3 = 40.907 MHz. (3) shows successive phase transitions at 121, 135, 165, and 208 K according to the NQR, DSC, and DTA measurements. Phase I of (3): at 293 K orthorhombic, Cmca, Z = 4, a = 783.4(4), b = 2480.2(10), c = 806.5(4) pm. 81Br NQR doublet was observed at 77 K (phase V) and at 300 K (Phase I) with ν1 = 61.060 and ν2 = 54.098 MHz (77 K); v1 = 55.835 and ν2 = 55.964 MHz (373 K). No NQR line could be observed in phases II, III, and IV.

A 81Br NQR study on structural phase transitions in (C nH 2 n+1 NH 3) 2ZnBr 4 crystals ( n = 1−4)

The temperature dependence of the 81Br NQR frequencies in (C n H 2 n+1 NH 3) 2ZnBr 4 ( n = 1−4) was measured above 77K. Four 81Br NQR lines were observed for all the compounds at 273K. It was found that (CH 3NH 3) 2 - . ( n-C 3H 7NH 3) 2 - and ( n-C 4H 9NH 3) 2ZnBr 4 undergo second-order structural phase transitions at 426, 298, and 299K, respectively. Above the transition temperatures three NQR lines were observed for the first two compounds, whereas only one signal could be detected for the last one. However, (C 2H 5NH 3) 2ZnBr 4 showed a first-order phase transition at 299.5K, above which temperature no NQR signal was observable. The nature of these phase transitions is discussed.

NQR study of [(CH 3) 2NH 2] 3InBr 6 and [4-ClC 5H 4NH] 2InBr 5(H 2O)

81Br, 115In, and 35Cl NQR spectra of dimethylammonium hexabromoindate(III)( 1) and 4-chloropyridinium pentabromoindate(III) monohydrate ( 2) were studied as a function of temperature. The 81Br 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 81Br NQR lines were found with frequencies (MHz, 298K) 74.09, 76.12, 84.52, 93.04 and 94.04. The intensities are equal. The 35Cl 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.

NQR and X-Ray Study of Bis(4-methylpyridinium) Pentabromoantimonate(III), (4-CH3C5H4NH)2SbBr5

Abstract The crystal structure of the title compound was determined (T = 300 K): , Z = 2, a = 1085.8, b = 1064.3, c = 929.0 pm, α = 97.83, β = 108.86, γ = 99.24°, R(F) = 0.047, Rw(F) = 0.041. Characteristic for the structure is the dimer structure of SbBr52− ion. The atomic coordination around the Sb atom is a distorted octahedron. The 81Br NQR spectrum was studied in the temperature range 77 ≤ T/K ≤ 350. The 81Br NQR frequencies are spread out over a wide range at 77 K: 37 ≤ ν(81Br)/MHz ≤ 111. The temperature dependence of the NQR frequencies and of their spread is given as is an assignment of 81Br NQR lines to the positions of Br atoms in the anion.

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 5 2h - 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): C5 2h - 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.

81Br NQR for Uncoordinated Br ions in trans-[CoBr2(en)2][H5O2]Br2 and trans-[CoBr2(en)2] [D5O2]Br2

Abstract The temperature dependence of the 81Br NQR frequencies (vD) for uncoordinated Br- ions in trans-[CoBr2(en)2] [D5O2]Br2(D) has been determined by a continuous-wave spectrometer. vD amounted to 16.200 MHz at 273 K. This is lower by 418 kHz than the 81Br NQR frequency (vH) for trans-[CoBr2 (en2] [H5O2 ]Br2 (H). The frequency difference (Δv = vH -vD) remained almost constant in the temperature range studied. A shortening of the O-H bond length caused by deuteration could explain the magnitude and the sign of Av on the basis of a point charge model calculation. The compounds D and H yielded 81Br NQR lines in the range 110-320 K and 90-343 K, respectively. As to the 59Co NQR frequencies (7/2 - 5/2), the observed isotope frequency shifts (Δv1 = v1H - v1D) between D and H were smaller than 5 kHz. Below 160 K, 59Co resonances were only available by pulsed experiments. 59Co NQR spin-lattice relaxation times T1Q of 0.54 ms at 194 K and 4.8 s at 77 K for H have been observed.

On the Symmetry of SbIIIBr63− and SbVBr6− Ions in the (NH4)4SbIIISbVBr12 Crystal. A Study of 81Br NQR Zeeman Effect

Abstract The single-crystal Zeeman effect was investigated for the 81Br NQR lines in the mixed-valence compound (NH4)4SbIIISbvBr12 at room temperature. Comparing with the results of X-ray analysis, it was concluded that the SbIIIBr63− ions possess D2d symmetry and the SbvBr6− ions possess D4h (nearly Oh) symmetry.

81Br NQR and 119Sn Mössbauer Spectra for SnBr3− Anions

Abstract The structures of the SnBr3− anions in MSnBr3 (M=(CH3)2NH2, (CH3)3NH) and MSnBr3·H2O (M=K, NH4) were deduced by means of 81Br NQR spectroscopy. The former compounds have three 81Br NQR lines in the frequency range 73–80 MHz at 77 K, indicating the presence of pyramidal SnBr3− anions. The anion structure of the latter hydrate, on the other hand, was presumed to be square-pyramid with one terminal and two bridging Br atoms, because two of the 81Br NQR frequencies were considerably low compared with that of the terminal atom. Phase transitions were observed for the latter hydrates. Associated with these, drastic increases of the NQR frequencies were observed only for the bridging atoms, suggesting significant changes in the bridging network.

Nuclear quadrupole resonances of α-(CH 3) 2 TeX 2 (X=Cl, Br, I) and (CH 3) 2 TeI 4

NQR spectra were observed for α-(CH 3) 2 TeX 2 (X=Cl, Br, I) and (CH 3) 2 TeI 4 at various temperatures. The two 81Br NQR lines were observed above 110 K in α-(CH 3) 2TeBr 2. The characteristic temperature dependence of the 127I NQR line in α-(CH 3) 2 TeI. can be explained by the 3c—4e bond of the linear ITeI group. The positive temperatures dependence of the lowest 127I NQR line in (CH 3) 2TeI 4 is discussed on the basis of the electron population calculated from Townes—Dailey treatment.