31P MAS NMR and DFT study of crystalline phosphate matrices

Laura Martel,Attila Kovács,Karin Popa,Damien Bregiroux,Thibault Charpentier

doi:10.1016/j.ssnmr.2019.101638

Abstract

We present the study of the phosphorus local environment by using 31P MAS NMR in a series of seven double monophosphates MIIMIV(PO4)2 (MII and MIV being divalent and tetravalent cations, respectively) of yavapaiite and low-yavapaiite type crystal structures. Solid-state and cluster DFT calculations were found to be efficient for predicting the 31P isotropic chemical shift and chemical shift anisotropy. To achieve this performance, however, a proper computational optimisation of the experimental structural data was required. From the three optimisation methods tested, the full optimisation provided the best reference structure for the calculation of the NMR parameters of the studied phosphates. Also, a better prediction of the chemical shifts was possible by using a correction to the GIPAW calculated shielding.

Highlights

Crystalline phosphates have aroused a lot of interest in the research community due to their numerous useful properties as ionic conductors[1], catalysts and ion exchangers[2] or luminescent materials and UV-emitting X-ray phosphors[3,4,5,6,7]
We show the optimisation effects on the experimental crystalline structures and how the NMR parameters can be predicted by means of solid-state and molecular quantum chemical codes utilizing density functional theory (DFT)
We studied here the local P environment in a series of crystalline phosphates by combing

Summary

Introduction

Crystalline phosphates have aroused a lot of interest in the research community due to their numerous useful properties as ionic conductors[1], catalysts and ion exchangers[2] or luminescent materials and UV-emitting X-ray phosphors[3,4,5,6,7]. Our present aim is to analyse the local structure around the P atom in such diamagnetic phosphates via density functional theory (DFT) calculations This knowledge can serve as basis for the understanding of the more complex NMR shifts of phosphates containing actinide or rare-earth cations. As the NMR signals,[28,29] are influenced by the paramagnetic interactions,[30,31,32] the use of the cluster model can successfully help in the prediction of the paramagnetic shifts as shown in our recent study[33] on the LaxEu1-xPO4 series in which an LaPO4 cluster was make This approach was applied by other authors in lithium batteries and is very promising.[34]

Methods

Results

Conclusion