dd Excitations in CPO-27-Ni Metal–Organic Framework: Comparison between Resonant Inelastic X-ray Scattering and UV–vis Spectroscopy

framework CPO-27-Ni by coupling resonant inelastic X-ray scattering (RIXS) and UV−vis spectroscopy, and we show that the element selectivity of RIXS is crucial to observing the full dd multiplet structure, which is not visible in UV−vis. The combination of calculations using crystal-field multiplet theory and density functional theory can reproduce the RIXS spectral features, crucially improving interpretation of the experimental data. We obtain the crystal-field splitting and magnitude of the electron−electron interactions and correct previously reported values. RIXS instruments at synchrotron radiation sources are accessible to all researchers, and the technique can be applied to a broad range of systems.