Structures and phase transitions of (BrCH2CH2NH3)2CdBr4 and (BrCH2CH2CH2NH3)2CdBr4 as investigated by 81Br NQR, DTA, and single-crystal X-ray diffraction

The crystal structures of (BrCH2CH2NH3)2CdBr4 (1) and (BrCH2CH2CH2NH3)2CdBr4 (2) have been determined at T = 113 K: orthorhombic, Pbcn, a = 843.8(4), b = 775.4(4), c = 2339.6(11) pm, Z = 4 for 1; orthorhombic, Pbcn, a = 858.7(3), b = 783.6(2), c = 2519.4(7) pm, Z = 4 for 2. Both crystals are isomorphic, showing distinctive layered perovskite-related structures, in which the cations orient their aliphatic parts toward each other in their cation layers and connect to the infinite anion layers with their ammonium parts through N–H · · · Br hydrogen bonds. 81Br NQR and differential thermal analysis measurements for both compounds revealed the existence of successive phase transitions as seen in n-(CH3CH2CH2NH3)2CdBr4 (3). These phase transitions appear to be induced by the activated motions of the cations. The changes in the hydrogen bonding schemes resulting from the motions of the cations lead to the different phases of the respective crystals.

Static and Dynamic Structures of InBrx (x = 1.4, 1.5, 1.75, and 2) Studied by 81Br NQR and 115In NMR

Structure and bonding properties of InBrx(In5Br7, In2Br3, In4Br7 and InBr2)were studied by 81Br and 115In NQR, and 115In NMR. The ethane-like [Br3InII-InIIBr3]2 anion was confirmed in In5Br7 or In2Br3 by 81Br NQR and the anion was characterized by the high quadrupole coupling constant at the 115In site (e2 Qq/h ≈ 350 MHz). On the other hand, In4Br7 showed successive phase transitions and was characterized as [InI]5[InIIIBr4]2[InIIIBr6] by means of 81Br NQR and 115In NMR below 370 K. A disordered structure at the cationic sublattice was supposed at Phase I above 370 K. NMR signals assigned to the InI could not be detected for the powdered sample, however, all quadrupole coupling constants ( e2Qq/h) and chemical shifts (δiso) could be determined using a single crystal. The InI sites show relatively large e2Qq/h and also show larger distribution of the chemical shift suggesting a diversity of the InI coordination similar to the isoelectronic main group elements such as SnII or SbIII .

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

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

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.