Calculation of NMR parameters in ionic solids by an improved self-consistent embedded cluster method

Abstract

A new embedded cluster method (extended embedded ion method = EEIM) for the calculation of NMR properties in non-conducting crystals is presented. It is similar to the Embedded Ion Method (EIM) (ref. 1) in the way of embedding the quantum chemically treated part in an exact, self-consistent Madelung potential, but requires no empirical parameters. The method is put in relation to already existing cluster models which are classified in a brief review. The influence of the cluster boundary and the cluster charge is investigated, which leads to a better understanding of deficiencies in EIM. A recipe for an improved semi-automated cluster setup is proposed which allows the treatment of crystals composed of highly charged ions and covalent networks. EIM and EEIM results for (19)F and (31)P shielding tensors in NaF and in four different magnesium phosphates are compared with experimental values from solid state MAS NMR, some of which are measured here for the first time. The quantum part of the clusters is treated at hybrid DFT level (mPW1PW) with atomic basis sets up to 6-311G(3df,3pd). The improved agreement of EEIM allows new signal assignments for the different P-sites in Mg(2)P(4)O(12), alpha-Mg(2)P(2)O(7) and MgP(4)O(11). Conversion equations of the type sigma = A + Bdelta between calculated absolute magnetic shieldings sigma and the corresponding experimental chemical shifts delta are obtained independently from linear regressions of plots of isotropically averaged sigma versus delta values on 19 (31)P signals of small molecules.

Computational 19F NMR. 1. General features

“…Some early computational work (aimed at benchmarking and validation) included F 2 as test molecule, which proved to be challenging [26][27][28]. Interest in modeling 19 F shifts has steadily continued, and several papers have appeared in the last decade aimed at general structural issues, solution chemistry and physical organic chemistry, [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] solid-state issues (especially the prediction of chemical shift tensors), [47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] J-couplings [65][66][67][68][69][70][71][72]…”

Density functional investigation of intermolecular effects on 13C NMR chemical-shielding tensors modeled with molecular clusters

“…43 Cluster models have associated problems, the most prominent among these being the extent and termination of the cluster. 44 Clusters must be designed to reflect the lattice structure around the NMR-active nucleus. This is often done by judiciously selecting several nearby molecules which are believed to influence the local electronic environment strongly.…”

Spin–orbit effects on the 119Sn magnetic-shielding tensor in solids: a ZORA/DFT investigation

“…37 Predicted isotropic 119 Sn chemical shifts in tin-containing solids calculated with plane-wave DFT techniques employing relativistic pseudopotentials at the ZORA level (without the SO component) are in good agreement with isotropic chemical shifts, although the calculated values do deviate by up to 200 ppm from experiment in some cases. 29,31,[46][47][48][49][50][51][52][53][54][55] The effect of hybrid functionals on computed magnetic shielding is also assessed. 16 In this study, we present calculations of the principal components of 119 Sn magneticshielding tensors for tin sites with different oxidation states and different co-ordination environments.…”