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1Author    Hiromitsu Terao, Masao Hashimoto\, Tsutomu Okuda, Alarich WeissRequires cookie*
 Title    Phase Transitions and Crystal Structure of Dimethylammonium Tribromomercurate(II), (CH 3 ) 2 NH 2 HgBr 3 , as Studied by 81 Br NQR and Single Crystal X-ray Diffraction  
 Abstract    The temperature dependence of the 81 Br NQR frequencies of the title compound has revealed the presence of three phases (I, II and III, in the order of decreasing temperature): T cl (II -1) = (318 ± 10) K and T c2 (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 (/. 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, ß = 104.10(1)°, Z= 8, R = 0.076. The crystal has two crystallographically independent cations (CH 3) 2 NH 2 + and an infinite chain of anions almost in the c-direction. The anion chain is considered to consist of a HgBr 2 molecule and two different HgBr 4 2 ~ anions which are interconnected via weak intermolecular Hg-Br bonds. The splitting patterns of the 8 'Br 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 81 Br NQR lines show anomalous temperature coefficients, attributable probably to thermal motions of cations. 
  Reference    Z. Naturforsch. 53a, 559—567 (1998); received January 26 1998 
  Published    1998 
  Keywords    (CH 3 ) 2 NH 2 HgBr 3, X-Ray Analysis, NQR, Phase Transition, Crystal Structure 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0559.pdf 
 Identifier    ZNA-1998-53a-0559 
 Volume    53