Deuterium NMR Study of Unstable Phenomena and Water Molecular Dynamics in Samarium Nitrate Hexahydrate Crystal

Abstract

Deuterium NMR spectra, spin-lattice relaxation time T 1 , and differential thermal analysis (DTA) were measured for Sm(NO 3 ) 3 ‚6D 2 O. The magnetization recovery can be divided into two components. From deuterium NMR spectra and T 1 , the short and the long components of T 1 were found to be mainly dominated by the 180°flip of the crystallization and the coordinated water molecules, respectively. For the nonannealed sample, the reproducibility of T 1 was observed. The influence of the instability was not seen in the long component of T 1 . The results of the long component of T 1 gave the activation energy E a ) 20 kJ mol -1 and the correlation time at infinite temperature τ c0 ) 7.8 × 10 -12 s for the 180°flip of the coordinated water molecule. The motion of the crystallization water at low temperatures can be explained by the 180°flip in the asymmetric double minimum potential. τ c0 ) 1.2 × 10 -12 s, E a ) 16 kJ mol -1 , and the energy difference in the potential wells ∆E ) 2.0 kJ mol -1 were obtained for the 180°flip of the crystallization water from the short component of T 1 . The potential wells for the 180°flip of the crystallization water changed gradually in phase II and approached the symmetric wells with increasing temperature. For the annealed sample, the drastic change of T 1 was observed in phases II and III. Both the long and the short components of T 1 did not show the reproducibility. These unstable phenomena are interpreted in terms of the metastable state due to the change of the hydrogen bond between the crystallization and the coordinated waters by annealing.

Deuterium Solid-State NMR Study of the Dynamic Behavior of Deuterons and Water Molecules in Solid D3PW12O40

“…The mobility of Brønsted sites in acidic zeolites has been well characterized by 1 H MAS NMR, 7,8 2 H wide-line solidstate NMR, 9,10 and impedance spectroscopy, 11 whereas information about the dynamics of both protons and water in HPAs still remains scarce. Qualitative results about the rate of proton migration 8,[12][13][14][15] and dynamics of water in H 3 PW 12 O 40 ‚nH 2 O 16 at temperatures below 373 K were reported, whereas quantitative information was reported only for water internal rotation in hexahydrate of HPA at 302-328 K 17 and for proton migration in anhydrous HPA at temperatures as high as 373 K. 18 Deuterium solid-state NMR ( 2 H NMR) spectroscopy has been shown many times to be a powerful technique to characterize the Brønsted acid sites and to probe the dynamics of protons and water in zeolites, 9,10,[19][20][21] intercalated in clay minerals, 22 in crystalline hydrates, 23,24 in cement systems, 25 on the surface of MCM-41, 26 in VPI-5 molecular sieve, 27 and in HPAs. 16,28 2 H NMR is one of the experimental techniques providing information on the characteristics of the motional behavior of water molecules in solids.…”

“…Deuterium solid-state NMR ( 2 H NMR) spectroscopy has been shown many times to be a powerful technique to characterize the Brønsted acid sites and to probe the dynamics of protons and water in zeolites, ,,− intercalated in clay minerals, in crystalline hydrates, , in cement systems, on the surface of MCM-41, in VPI-5 molecular sieve, and in HPAs. , 2 H NMR is one of the experimental techniques providing information on the characteristics of the motional behavior of water molecules in solids. The line shape for 2 H NMR, being completely defined by intramolecular quadrupole interaction, − is especially sensitive to the mode of molecular motion and to its rate; , spin−lattice relaxation time is also dependent on the rate and mode of motion.…”

Massive enhancement of persistent spectral hole-burning in the R-lines of NaMgAl(oxalate)3·9H2O:Cr(III) by partial deuteration

“…The present system shows the opposite effect and hence cannot be accounted for by the standard tunneling model. It is well documented that water molecules of crystallization can undergo rapid 180°flip motions at room temperature and activation barriers of 10-60 kJ/mol have been measured by solid state NMR spectroscopy [18,19]. The 180°flip motion may thus provide an explanation for the enormous increase in the holeburning efficiency and the appearance of sharp anti-holes upon partial deuteration.…”

Molecular Dynamics in Paramagnetic Materials as Studied by Magic-Angle Spinning 2H NMR Spectra

“…11,12 The simulation method for the 2 H NMR broadline spectrum of paramagnetic compounds obtained by these pulse sequences has been developed for the study of molecular dynamics in paramagnetic compounds. 2,[13][14][15][16][17][18][19] 2 H magic-angle spinning (MAS) NMR spectra with spinning sidebands have also been shown to be sensitive to molecular motions with the rates, 10 2 s -1 e k e 10 3 s -1 and 10 7 s -1 e k e 10 9 s -1 , which are almost undetectable in the 2 H NMR broadline spectra. [25][26][27] Therefore, information of molecular motions in a wide dynamic range can be obtaind by the combined use of 2 H NMR MAS and broadline spectra.…”