Experimentally Established Benchmark Calculations of ³¹P NMR Quantities

Abstract

The accuracy of different density function theory functionals and the MP2 approximation in 31P NMR calculations has been evaluated for ten phosphorous containing molecules in which the phosphorous atoms are not involved in intermolecular interactions. The obtained absolute chemical shielding tensors are compared to experimental ones. The dependence of the numerical values on the size of basis sets has been inspected from the 6‐311G(2d,p) to the pcSseg‐3 basis sets. General recommendations on the most reliable functionals and the smallest possible size of a basis set have been reported. For example, the use of the M06 L functional should be avoided. For five polycrystalline samples, the conformation of molecules has been identified with a high precision. These structures have been used to determine the reference values of the absolute chemical shielding for the TPSSh, B3LYP, and ωB97XD functionals and different basis sets. As reported in the supporting information, these structures can be used to determine the reference value of the absolute chemical shielding for any approximation of interest.

1,3,5-Triaza-7-Phosphaadamantane (PTA) as a 31P NMR Probe for Organometallic Transition Metal Complexes in Solution

“…This value is easy to measure but not to calculate. Recently, the reference values of the absolute chemical shielding, σ ref ( 31 P), have been reported for a number of approximations [ 34 ]. PTA was among the used model compounds.…”

“…The values of σ ref ( 31 P) calculated under the w B97XD/Def2QZVP and w B97XD/Def2TZVP approximations using PTA as the reference compound are σ ref ( w B97XD/Def2QZVP) = 308 ppm and σ ref ( w B97XD/Def2TZVP) = 306 ppm; these values are valid under the PCM approximations as well ( Table S1, Supplementary Materials ). The expected margin of error is ±5 and ±9 ppm, respectively [ 34 ]. In this paper, the calculated isotropic values of the absolute chemical shielding were converted into the isotropic chemical shifts to compare the calculated values with experimental data, δ iso = (σ ref − σ iso ).…”

“…31 P NMR chemical shift may depend on the conformation of the attached groups [ 25 ]. This effect is absent for rigid molecules, such as 1,3,5-triaza-7-phosphaadamantane (PTA, Figure 1 ) and 2,8,9-trioxa-1-phosphadamantane [ 34 ]. PTA is especially useful as an NMR probe because its phosphorus atom is chemically inert.…”

“…PTA is especially useful as an NMR probe because its phosphorus atom is chemically inert. Its 31 P NMR chemical shift in the crystalline phase can be reproduced correctly in single molecule Density Functional Theory (DFT) calculations [ 34 ] without the need to use the gauge-including projector augmented wave (GIPAW) approach [ 35 , 36 ]. In acidic solution, PTA would be protonated at one of its nitrogen atoms.…”

Solid State NMR for Nonexperts: An Overview of Simple but General Practical Methods

“…Therefore, δ( 31 P) is known, but the corresponding σ( 31 P) cannot be calculated, so σ ref ( 31 P) remains unknown. For 31 P this problem has been solved recently [34]. The values of δ( 31 P) were measured for a number of solids in which δ( 31 P) was not influenced by noncovalent interactions, Figure 4.…”