Dynamic three-dimensional structures of a metal–organic framework captured with femtosecond serial crystallography

Novel crystalline materials consisting of organic, inorganic or organometallic building blocks have emerged as promising materials with wide applications [1-5]. Of great importance is to characterize not only the static structures of those materials grown in single crystals but also the conversion of their structures in response to external stimuli [6, 7]. Femtosecond time-resolved crystallography has the potential to probe real-time dynamics of such structural conversions but has not yet been realized for chemical reactions in crystals made of small-molecule building blocks. Here, we apply time-resolved serial femtosecond crystallography (TR-SFX), a powerful technique for visualizing protein structural dynamics, to a metal–organic framework consisting of Fe-porphyrins and Zr6 nodes and elucidate the real-time structural dynamics initiated by the ligand photodissociation. The time-resolved electron density maps from the TR-SFX data unveil trifurcating structural pathways: (i) coherent oscillatory movements of Zr and Fe atoms, assigned to an optical phonon mode of 0.18 THz, (ii) a transient structure with Fe-porphyrin and Zr6 node undergoing doming and disordering movements, respectively, and (iii) a vibrationally hot structure with isotropic structural disorder, which is rarely observed in protein crystals. These findings demonstrate the feasibility of TR-SFX measurement on chemical systems.