# On the preparation and NMR spectroscopic characterization of potassium aluminium tetrahydride KAlH4

## TL;DR

This study synthesized high-purity potassium aluminium tetrahydride using mechanochemistry and characterized it with detailed NMR spectroscopy, providing precise isotropic chemical shifts and quadrupole coupling data.

## Contribution

It presents a straightforward NMR spectroscopic method for characterizing complex aluminium hydrides and similar materials with half-integer nuclei.

## Key findings

- High phase purity of KAlH4 achieved via mechanochemical synthesis
- Precise NMR parameters for 27Al and 39K at room temperature
- Method applicable to other complex aluminium hydrides

## Abstract

Potassium aluminium tetrahydride KAlH4 of high phase purity (space group Pnma (62)) was synthesized via a mechanochemical route. The thus obtained material was studied by 27Al and 39K MAS NMR spectroscopy. For both nuclei precise data for the isotropic chemical shift and the quadrupole coupling at T=295 K were derived (27Al: delta_iso=(107.6+-0.2) ppm, C_Q = (1.29+-0.02) MHz and eta = 0.64+-0.02; 39K: delta_iso=(6.1+-0.2) ppm, C_Q = (0.562+-0.005) MHz and eta = 0.74+-0.02). The straightforward NMR spectroscopic approach applied here should also work for other complex aluminium hydrides and for many other materials containing half-integer nuclei experiencing small to medium-sized quadrupole couplings.