NMR Studies of NaH

Abstract

Hydrogen and 23 Na NMR were used to probe diffusive motions of the ions in several NaH powders. In three NaH samples, the H resonance is a superposition of broad and narrow components, reflecting the presence of relatively immobile and mobile H, respectively. The fraction of mobile H grows from 23 to 250 °C; this pattern has been observed previously in other ionic hydrides. By 300 °C, the formerly broad hydrogen component has itself motionally narrowed. In these samples, the observation of a smaller amount of 23 Na line narrowing by 300 °C indicates that only the H − ions are mobile at 300 °C, leaving 23 Na− 23 Na dipole interactions unaveraged. A deep minimum in the hydrogen rotating-frame relaxation time T 1ρ is observed near 325 °C, as expected from the onset of motional averaging. In a fourth sample, the entire H line is narrowed already by 150 °C. In this sample, the 23 Na is also partially narrowed at this temperature and by 175−225 °C, further narrowing of the 23 Na resonance indicates that now both ions are in rapid motion. In all the samples, the spin−lattice relaxation times T 1 for hydrogen and sodium decrease monotonically with temperature, in qualitative accord with relaxation by physical diffusion of spin magnetization to relaxation centers.

Extrinsic Proton NMR Studies of Mg(OH)2 and Ca(OH)2

“…The temperature-induced 1 H NMR spectra and the two-component spectra have been observed for MgH 2 [3], LiBH 4 [4], NaMgH 3 [5], NaH [6], and the KH 2 PO 4 family [7,8].…”

“…Ionic conduction facilitated by lattice defects also causes the narrowing of the NMR spectra [2]. The development of a narrow NMR spectrum superposed with a broad NMR spectrum has been observed for some hydrates [3][4][5][6], hydrogen-bonded compounds [7,8], and nanocrystalline Li compounds [9][10][11]. The broad component is assigned to immobile ions with dipole-dipole couplings on a rigid lattice, while the narrow component is assigned to mobile ions decoupled from the matrix of each material.…”

1H NMR Studies of MgH2

“…The dominant contribution of the linewidth of the broad component in the coarse-bm MgH 2 sample is dipolar broadening from homonuclear interaction ( 1 H-1 H) on a rigid lattice [2,4]. Then, the larger linewidth of the present sample than that of the coarse-bm sample indicates that the present sample forms more inhmogeneous rigid lattice than the coarse-bm sample.…”

Formation of Frustrated Lewis Pairs in Ptx‐Loaded Zeolite NaY

“…Thus,a saresult of the high nuclear spin value of 23 Na (I = 3/2 > 1), the nuclear quadruple interaction, which is represented by the electric field gradient around the nucleus, should be involved in the spin Hamiltonian. [20] This phenomenon is attributed to the reduction of the electric field gradient anisotropy around the sodium nuclei because of the hydride ions bonded to them. [20] This phenomenon is attributed to the reduction of the electric field gradient anisotropy around the sodium nuclei because of the hydride ions bonded to them.…”