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1998 (1)
1991 (1)
1Author    Motohiro Mizuno, Tetsuo Asaji, Atsushi Tachikawa, The Late, Daiyu NakamuraRequires cookie*
 Abstract    h lo r in e N Q R S p in -L a ttic e R e la x a tio n a n d E le c tro n S p in D y n a m ic s in P a r a m a g n e tic [ C o (H 20) 6] I P tC l 6| Chlorine NQR spin-lattice relaxation times T1Q were determined for [Co(H,0)6][PtCl6] at 4.2 400 K. Above ca. 350 K, T1Q decreased rapidly showing the onset of a reorientation of [PtCl6]2-. The activation energy Ea of this reorientation was determined as 125 ± 15 kJ mol ~1. With decreasing temperature, Tlfi showed a maximum at ca. 250 K. Below ca. 200 K, Tl(. is governed by the magnetic dipolar interaction between chlorines and paramagnetic Co2+ ions and is inversely proportional to the electron spin correlation time re of Co2 . Te is shown to be determined by the electron spin-lattice relaxation time Tle and the temperature independent correlation time rs for the spin-exchange between neighbouring ions above and below ca. 50 K, respectively. The temperature dependence of Tle is explained by assuming the Orbach process with an energy gap A/k of 530 + 20 K as Tle = 5 x 10~14 exp(530/T)s. ts was estimated to be 0.9 x 10"10 s. The temperature dependence of the ESR linewidth of Mn2+ impurities in single crystal was also measured, intending to study Co2+ spin dynamics. The limit of the ESR method is discussed by comparing the obtained results with those of the NQR method. 
  Reference    Z. Naturforsch. 46a, 1103 (1991); received September 17 1991 
  Published    1991 
  Keywords    Spin-lattice relaxation, NQR, ESR, Reorientation, Orbach process 
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 TEI-XML for    default:Reihe_A/46/ZNA-1991-46a-1103.pdf 
 Identifier    ZNA-1991-46a-1103 
 Volume    46 
2Author    Takahiro Ueda, Katsuyuki Shimizu, Hiroshi Ohki, Tsutomu OkudaRequires cookie*
 Title    C CP/MAS NMR Study of Motion and Local Structure of Phenethyl- ammonium Ion in [C 6 H 5 CH 2 CH 2 NH 3 ] 2 PbX 4 (X = Cl, Br, I)  
 Abstract    Ionic motion and local structure of phenethylammonium ion (C 6 H 5 CH-,CH 2 NH 3 +) in a series of phenethylammonium lead(II) halides, [C 6 H 5 CH 2 CH 2 NH 3 ] 2 PbX 4 (X = Cl, Br, I) were studied by means of 13 C cross polarization/magic angle sample spinning (CP/MAS) NMR technique. Among the three salts, remarkable differences in the spectra were observed in the signals corresponding to the phenyl carbons. The peaks from C2, C3, C5, and C6 in the phenyl group were split into three for the chloride and into two for the bromide, although in the iodide those were observed as a single peak. Coalescence of those peaks, as well as line broadening were observed on heating. This indicated that peak split brings about disorder of the orientation in the phenyl group around the C1-C4 axis, suggesting to have three and two orientations for the chloride and the bromide, respectively. Above room temperature the phenyl group undergoes chemical exchange among these orientations, and at higher temperature, reorientation with a large amplitude takes place around its axis. The apparent activation energies of the reorientation of the phenyl group for the chloride and bromide were estimated from the temperature dependence of the linewidth of the resonance peaks to be about 24 kJ mol -1 , 25 kJ mol -1 , respectively, which is similar to in the iodide (25.0 kJ mol -1). Ab initio molecular orbital energy calculation was carried out to evaluate the potential barrier of the internal rotation of the phenyl group in a free phenethylammonium ion. The intramolecular interaction was evaluated to be 13.9 kJ mol -1 from the calculation, and the intermolecular interaction results to be 10 kJmol -1 . 
  Reference    Z. Naturforsch. 53a, 983—988 (1998); received April 30 1998 
  Published    1998 
  Keywords    13 C CP/MAS NMR, Layered compound, Disorder, Reorientation, Activation energy 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0983.pdf 
 Identifier    ZNA-1998-53a-0983 
 Volume    53