In:
Canadian Journal of Chemistry, Canadian Science Publishing, Vol. 77, No. 11 ( 1999-11-01), p. 1813-1820
Abstract:
Deuterium and nitrogen-15 NMR spectroscopy has been used to measure the 2 H quadrupolar coupling and 15 N chemical shift tensors in solid hydroxylammonium chloride, NH 3 OH + Cl - , (HAC). In addition, the NH 3 and OH dynamics have been investigated by variable temperature 2 H line shapes and T 1 measurements. The Arrhenius activation energy for NH 3 rotation is 22.5 ± 1.8 kJ/mol with a pre-exponential factor of 8 ± 3 × 10 12 s -1 from line shapes and 21.3 ± 2 kJ/mol with an infinite temperature correlation time, τ inf, , of 5.0 ± 0.4 × 10 -14 s from the T 1 analysis. The latter value corresponds to a pre-exponential factor of 6.7 ± 0.5 × 10 12 s -1 , if a three-site exchange is assumed. There was no evidence for OH reorientation up to 405 K, indicating a rather strong OH···Cl hydrogen bond. Previously reported inconsistencies between crystal structure and molecular orbital derived N-O bond lengths are cleared up by performing geometry optimizations with large basis sets and taking electron correlation into account. The internal rotational potential for the isolated HA cation is calculated to be 5.8 kJ/mol at the MP2/6-31G** level, with the trans geometry preferred. Calculations that employ the neutron diffraction geometry and include the Cl - anions that surround the HA + cation yield an upper limit for the activation energy for NH 3 group rotation of 62 kJ/mol. Analysis of the deuterium spectrum and T 1 data yield nuclear quadrupolar coupling constants of 160 ± 5 kHz and 194 ± 5 kHz (η = 0.50 ± 0.05) for the ND 3 and OD deuterons, respectively. Density functional calculations of the deuterium and nitrogen-14 nuclear quadrupolar coupling constants at the B3LYP level show that it is necessary to include the influence of the surrounding chloride anions. We have also shown that it is possible to obtain accurate proton chemical shifts from the deuterium MAS spectrum of solid HAC-d 4 .Key words: solid state NMR, molecular dynamics, nitrogen 15 chemical shift anisotropy.
Type of Medium:
Online Resource
ISSN:
0008-4042
,
1480-3291
Language:
English
Publisher:
Canadian Science Publishing
Publication Date:
1999
detail.hit.zdb_id:
2988-9
detail.hit.zdb_id:
1482256-8
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