TY - JOUR
T1 - Deciphering the NMR fingerprints of the disordered system with quantum chemical studies
AU - Ling, Yan
AU - Zhang, Yong
PY - 2009/5/21
Y1 - 2009/5/21
N2 - Recent developments in solid-state NMR techniques helped acquire high-resolution NMR spectra for solid systems with structural disorder. But the structural origin of the observed chemical shift nonequivalence in these systems has not been revealed. We report a quantum chemical investigation of the solid-state NMR spectrum in N,N-bis(diphenylphosphino)-N-((S)-α- methylbenzyl)amine, where eight nonequivalent 31P NMR chemical shifts were resolved with a range of 13.0 ppm. Results from using different quantum chemical methods, computational algorithms, intermolecular effects, and structures indicate that for the disordered system, geometry optimization gives the best accord with experimental NMR chemical shifts, which has a theory-versus-experiment correlation R 2 = 0.949 and SD = 1.1 ppm, or R 2 = 0.994 and SD = 0.4 ppm when the average of two unassigned NMR shifts for each molecule is used. In addition, these calculations indicate that the experimental chemical shift nonequivalence in this system is mainly a consequence of the different geometries around the phosphorus atoms due to disordered environments. The experimental 31P NMR chemical shifts are well correlated (R 2 = 0.981) with two conformation angles and one bond length, each associated with one of the three bonding interactions around the phosphorus atoms. These results will facilitate the use of quantum chemical techniques in structural characterization of disordered solids and elucidation of NMR properties.
AB - Recent developments in solid-state NMR techniques helped acquire high-resolution NMR spectra for solid systems with structural disorder. But the structural origin of the observed chemical shift nonequivalence in these systems has not been revealed. We report a quantum chemical investigation of the solid-state NMR spectrum in N,N-bis(diphenylphosphino)-N-((S)-α- methylbenzyl)amine, where eight nonequivalent 31P NMR chemical shifts were resolved with a range of 13.0 ppm. Results from using different quantum chemical methods, computational algorithms, intermolecular effects, and structures indicate that for the disordered system, geometry optimization gives the best accord with experimental NMR chemical shifts, which has a theory-versus-experiment correlation R 2 = 0.949 and SD = 1.1 ppm, or R 2 = 0.994 and SD = 0.4 ppm when the average of two unassigned NMR shifts for each molecule is used. In addition, these calculations indicate that the experimental chemical shift nonequivalence in this system is mainly a consequence of the different geometries around the phosphorus atoms due to disordered environments. The experimental 31P NMR chemical shifts are well correlated (R 2 = 0.981) with two conformation angles and one bond length, each associated with one of the three bonding interactions around the phosphorus atoms. These results will facilitate the use of quantum chemical techniques in structural characterization of disordered solids and elucidation of NMR properties.
UR - http://www.scopus.com/inward/record.url?scp=66149181901&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=66149181901&partnerID=8YFLogxK
U2 - 10.1021/jp9001324
DO - 10.1021/jp9001324
M3 - Article
C2 - 19331332
AN - SCOPUS:66149181901
SN - 1089-5639
VL - 113
SP - 5993
EP - 5997
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 20
ER -