The role of carboxylate ligand orbitals in the breathing dynamics of a metal-organic framework by resonant X-ray emission spectroscopy

Metal-organic frameworks (MOFs) exhibit structural flexibility induced by temperature and guest adsorption, as demonstrated in the structural breathing transition in certain MOFs between narrow-pore and large-pore phases. Soft modes were suggested to entropically drive such pore breathing through enhanced vibrational dynamics at high temperatures. In this work, oxygen K-edge resonant X-ray emission spectroscopy of the MIL-53(Al) MOF was performed to selectively probe the electronic perturbation accompanying pore breathing dynamics at the ligand carboxylate site for metal – ligand interaction. It was observed that the temperature-induced vibrational dynamics involves switching occupancy between antisymmetric and symmetric configurations of the carboxylate oxygen lone pair orbitals, through which electron density around carboxylate oxygen sites is redistributed and metal – ligand interactions are tuned. In turn, water adsorption involves an additional perturbation of π orbitals not observed in the structural change solely induced by temperature.

Source: Journal of Synchrotron Radiation - February 16, 2024 Category: Physics Authors: Ugalino, R. Yamazoe, K. Miyawaki, J. Kiuchi, H. Kurahashi, N. Kosegawa, Y. Harada, Y. Tags: resonant X-ray emission spectroscopy phase transition metal-organic framework research papers Source Type: research