# Molecular Dynamics in Tetrafluoridoborate Salts of Divalent Metals Studied by Nuclear Magnetic Resonance Spectroscopy

## TL;DR

This study uses NMR to investigate molecular motion in tetrafluoridoborate salts of divalent metals, comparing their dynamics to similar compounds.

## Contribution

Quantitative activation energies for BF4− reorientations in M(BF4)2 salts are determined and compared to borohydrides.

## Key findings

- Activation energies for BF4− reorientations were measured in Ca(BF4)2, Sr(BF4)2, Ba(BF4)2, and Cd(BF4)2.
- Dynamics in tetrafluoridoborate salts were compared to those in borohydride systems with similar tetrahedral geometries.
- Temperature-dependent NMR data revealed thermally activated motions of BF4− ions in these salts.

## Abstract

Fluoridoborate (BF4
−) salts are linchpins across synthesis and catalysis, key constituents of ionic liquids, and promising electrolytes and additives in next‐generation multivalent rechargeable batteries. Despite this reach, quantitative links between crystal chemistry and anion motion remain scarce. Here, we present a molecular dynamics study of four such salts, namely M(BF4)2 (M = Ca2+, Sr2+, Ba2+, Cd2+), by means of nuclear magnetic resonance spectroscopy (NMR). We measured the temperature dependence of static 19F NMR spectra and spin‐lattice relaxation and determined the values of activation energies for the thermally‐activated reorientations for the BF4
− tetrahedra. We draw a comparison with systems with similar geometries, such as the well‐studied complex metal borohydrides.

We studied molecular dynamics in four tetrafluoridoborate salts by means of nuclear magnetic resonance. Characteristical motions in these systems are thermally‐activated reorientations of BF4
− ions. We determine the activation energies for these processes and compare the dynamics with those in borohydride systems that share the tetrahedral geometry of the anions.© 2026 WILEY‐VCH GmbH