Effect of Molecular Guest Binding on the d–d Transitions of Ni 2+ of CPO-27-Ni: A Combined UV–Vis, Resonant-Valence-to-Core X-ray Emission Spectroscopy, and Theoretical Study

DOI: 10.1021/acs.inorgchem.7b01471

Authors: Erik Gallo (University of Turin; European Synchrotron Radiation Facility (ESRF)) , Evgeny Gorelov (European XFEL GmbH) , Alexander A. Guda (International Research Center “Smart Materials”, Southern Federal University) , Aram L. Bugaev (University of Turin; International Research Center “Smart Materials”, Southern Federal) , Francesca Bonino (University of Turin) , Elisa Borfecchia (University of Turin) , Gabriele Ricchiardi (University of Turin) , Diego Gianolio (Diamond Light Source) , Sachin Chavan (University of Oslo) , Carlo Lamberti (International Research Center “Smart Materials”, Southern Federal University; University of Turin)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Inorganic Chemistry

State: Published (Approved)
Published: October 2017

Abstract: We used Ni K-edge resonant-valence-to-core X-ray emission spectroscopy (RVtC-XES, also referred to as direct RIXS), an element-selective bulk-sensitive synchrotron-based technique, to investigate the electronic structure of the CPO-27-Ni metal–organic framework (MOF) upon molecular adsorption of significant molecular probes: H2O, CO, H2S, and NO. We compare RVtC-XES with UV–vis spectroscopy, and we show that the element selectivity of RVtC-XES is of strategic significance to observe the full set of d–d excitations in Ni2+, which are partially overshadowed by the low-energy π–π* transitions of the Ni ligands in standard diffuse-reflectance UV–vis experiments. Our combined RVtC-XES/UV–vis approach provides access to the whole set of d–d excitations, allowing us a complete discussion of the changes undergone by the electronic configuration of the Ni2+ sites hosted within the MOF upon molecular adsorption. The experimental data have been interpreted by multiplet ligand-field theory calculations based on Wannier orbitals. This study represents a step further in understanding the ability of the CPO-27-Ni MOFs in molecular sorption and separation applications.

Subject Areas: Chemistry

Facility: ESRF