Mapping the complete bonding network in KBH4 using the combined power of powder diffraction and maximum entropy method

Abstract The combined power of the maximum entropy method (MEM) and synchrotron powder X-ray diffraction (SPXRD) is exerted to accurately reconstruct the electron density distribution (EDD) of the hydrogen storage material, KBH 4 . Its crystal structure features thermally activated disorder among the BH 4 - moieties, and weak secondary bonding effects occupy a key role in determining the energetic barrier for this dynamical effect. The MEM reconstruction is meticulously optimised and inspected for errors, in what may be envisaged as a general manual for this kind of studies. The successful outcome constitutes an experimental EDD of cutting-edge quality, from which atomic charges and the complete bonding network are mapped by topological descriptors. Remarkably, the chemical insights even extend to the delicate interplay of closed-shell bonding in excellent correspondence with ab initio and two-channel MEM calculations. For the current class of functional materials, access to such subtle electronic features is essential for the fundamental understanding of hydrogen desorption pathways.