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

Fluoridoborate (BF 4 − ) 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(BF 4 ) 2 (M = Ca 2+ , Sr 2+ , Ba 2+ , Cd 2+ ), by means of nuclear magnetic resonance spectroscopy (NMR). We measured the temperature dependence of static 19 F NMR spectra and spin‐lattice relaxation and determined the values of activation energies for the thermally‐activated reorientations for the BF 4 − tetrahedra. We draw a comparison with systems with similar geometries, such as the well‐studied complex metal borohydrides.