31P chemical shielding as a function of bond angle: phosphorus chemical shielding surface of phosphinoborane R2PBR'2

1999 ◽  
Vol 77 (11) ◽  
pp. 1951-1961 ◽  
Author(s):  
Michael JT Ditty ◽  
William P Power
Keyword(s):  
Solid State ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Principal Components ◽  
Bond Angle ◽  
Good Description ◽  
Chemical Shielding ◽  
Orbital Theory ◽  
Shielding Tensor ◽  
Theory Calculation

The phosphorus chemical shielding surface of phosphinoborane R2PBR'2 has been investigated via molecular orbital theory calculation and experimental measurement of selected derivatives. Ab initio calculations of phosphorus chemical shielding tensors were determined for the phosphinoboranes H2PBH2 and (CH3)2PB(CH3)2. Changes in the angle from planarity, i.e., that between the P-BR'2 plane and the bisector of the RPR angle, are reflected in the orientations and magnitudes of the three principal components of the phosphorus chemical shielding tensor. To determine the validity of the calculated phosphorus chemical shielding surface, three phosphinoborane compounds with different angles from planarity were synthesized and studied by solid-state 31P NMR spectroscopy. The 31P NMR powder patterns provided experimental magnitudes of the principal components of the phosphorus chemical shielding tensor for each compound, which compared well to the calculated predictions; where orientations of these tensors could be determined experimentally, they also agreed well with the calculated results. The combined experimental and theoretical results provide a good description of the effects on changes in bond angle on phosphorus chemical shielding as the molecule is distorted from a planar to folded geometry.Key words: chemical shielding, solid-state NMR, phoshinoborane, ab initio calculations.

Characterization of phosphorus chemical shielding tensors in a phosphole tetramer: a combined experimental and theoretical study

2000 ◽  
Vol 78 (1) ◽  
pp. 118-127 ◽  
Author(s):  
Myrlene Gee ◽  
Roderick E Wasylishen ◽  
Klaus Eichele ◽  
Gang Wu ◽  
T Stanley Cameron ◽  
...  
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Nmr Spectra ◽  
Spin Echo ◽  
Relative Orientation ◽  
Chemical Shielding ◽  
Spin Pair ◽  
Shielding Tensors ◽  
Shielding Tensor ◽  
Spin Pairs

Phosphorus-31 1D NMR spectra of a stationary powder sample of a phosphole tetramer containing two phosphorus spin pairs have been obtained at 4.7 T and 9.4 T. In order to separate 31P-31P spin-spin coupling from anisotropic chemical shielding, 2D spin-echo NMR spectra have been acquired. Phosphorus-31 CPMAS NMR experiments indicate that the two spin pairs of the tetramer are equivalent and each may be treated as an isolated spin pair. Within a given spin pair, the difference between the isotropic chemical shifts of two directly bonded phosphorus nuclei is 1.7 ppm. As well, they are spin-spin coupled by both the indirect and direct interactions, 1J(31P, 31P) = -362 Hz and RDD = 1.80 kHz, respectively. The principal components and relative orientation of the two phosphorus chemical shielding tensors have been determined using the dipolar-chemical shift technique; however, since the dipolar tensor is axially symmetric, ambiguities in the chemical shielding tensor orientation relative to the molecular framework result. Using ab initio calculations and simulations of the 2D spin-echo spectra, many of these ambiguities have been resolved. The spans and skews of the phosphorus shielding tensors for all four three-coordinate phosphorus nuclei are the same within experimental error, 115 ppm and 0.70, respectively. Combined experimental and theoretical results indicate that the phosphorus shielding tensor orientations are dictated by the local environment. For both shielding tensors, the most shielded component, δ33, is approximately 78° from the P-P bond and in the phosphole ring plane. The relative orientation of the δ33 components is described by a dihedral angle of 82°, similar to the dihedral angle of approximately 76° defining the twist of the phosphole rings about the bridging P-P bond.Key words: solid-state 31P NMR, phosphorus chemical shielding tensors, phosphole tetramer, 31P—31P spin pairs, ab initio calculations.

scholarly journals Coupling Solid-State NMR with GIPAW ab Initio Calculations in Metal Hydrides and Borohydrides

2013 ◽  
Vol 117 (19) ◽  
pp. 9991-9998 ◽  
Author(s):  
Federico Franco ◽  
Marcello Baricco ◽  
Michele R. Chierotti ◽  
Roberto Gobetto ◽  
Carlo Nervi
Keyword(s):  
Solid State ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Solid State Nmr ◽  
Metal Hydrides

Nuclear magnetic shielding tensors for the carbon, nitrogen, and selenium nuclei of selenocyanates - a combined experimental and theoretical approach

2000 ◽  
Vol 78 (5) ◽  
pp. 614-625 ◽  
Author(s):  
Guy M Bernard ◽  
Klaus Eichele ◽  
Gang Wu ◽  
Christopher W Kirby ◽  
Roderick E Wasylishen
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Axially Symmetric ◽  
Paramagnetic Contribution ◽  
Shielding Tensors ◽  
The Difference ◽  
Shielding Tensor ◽  
Angle Spinning

The principal components of the carbon, nitrogen, and selenium chemical shift (CS) tensors for several solid selenocyanate salts have been determined by NMR measurements on stationary or slow magic-angle-spinning powder samples. Within experimental error, all three CS tensors are axially symmetric, consistent with the expected linear geometry of these anions. The spans (Ω) of the carbon and selenium CS tensors for the selenocyanate anion (SeCN-) are approximately 300 and 800 ppm, respectively, much less than the corresponding values for carbon diselenide (CSe2). This difference is a consequence of the difference in the CS tensor components perpendicular to the C infiniti symmetry axes in these systems. Ab initio calculations show that the orbital symmetries of these compounds are a significant factor in the shielding. For CSe2, efficient mixing of the σ and π orbitals results in a large paramagnetic contribution to the total shielding of the chemical shielding tensor components perpendicular to the molecular axis. Such mixing is less efficient for the SeCN-, resulting in a smaller paramagnetic contribution and hence in greater shielding in directions perpendicular to the molecular axis.Key words: selenocyanates, solid-state NMR, carbon shielding tensors, nitrogen shielding tensors, selenium shielding tensors, ab initio calculations.

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