The chemistry of electrons in actinide complexes and materials is still poorly understood and represents a serious challenge and opportunity for experiment and theory. The study of the electron density distribution of the ground state of such systems through X-ray diffraction represents a unique opportunity to quantitatively investigate different chemical bonding interactions at once, but was considered "almost impossible" on heavy-atom systems, until very recently. Here, we present a combined experimental and theoretical investigation of the electron density distribution in UCL4 crystals and comparison with the previously reported spin density distribution from polarized neutron diffraction. All approaches provide a consistent picture in terms of electron and spin density distribution, and chemical bond characterization. More importantly, the synergy between experiments and quantum-mechanical calculations allows to highlight the remarkable sensitivity of X-ray diffraction to electrons in materials.
Keywords: 5 f electrons; Actinides; Quantum theory of atoms in molecules; Uranium; X-ray diffraction.
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