Characterization of Deformational Isomerization Potential and Interconversion Dynamics with Ultrafast X-ray Solution Scattering

Natalia E. Powers-Riggs, Benedikt O. Birgisson, Sumana L. Raj, Elisa Biasin, Philipp Lenzen, Diana Bregenholt Zederkof, Morten Haubro, Dagrún K.V. Tveiten, Robert W. Hartsock, Tim B. van Driel, Kristjan Kunnus, Matthieu Chollet, Joseph S. Robinson, Silke Nelson, Ruaridh Forbes, Kristoffer Haldrup, Kasper S. Pedersen, Gianluca Levi, Asmus Ougaard Dohn, Hannes JónssonKlaus Braagaard Mo̷ller, Adi Natan*, Martin Meedom Nielsen*, Kelly J. Gaffney*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Dimeric complexes composed of d8 square planar metal centers and rigid bridging ligands provide model systems to understand the interplay between attractive dispersion forces and steric strain in order to assist the development of reliable methods to model metal dimer complexes more broadly. [Ir2 (dimen)4]2+ (dimen = para-diisocyanomenthane) presents a unique case study for such phenomena, as distortions of the optimal structure of a ligand with limited conformational flexibility counteract the attractive dispersive forces from the metal and ligand to yield a complex with two ground state deformational isomers. Here, we use ultrafast X-ray solution scattering (XSS) and optical transient absorption spectroscopy (OTAS) to reveal the nature of the equilibrium distribution and the exchange rate between the deformational isomers. The two ground state isomers have spectrally distinct electronic excitations that enable the selective excitation of one isomer or the other using a femtosecond duration pulse of visible light. We then track the dynamics of the nonequilibrium depletion of the electronic ground state population─often termed the ground state hole─with ultrafast XSS and OTAS, revealing a restoration of the ground state equilibrium in 2.3 ps. This combined experimental and theoretical study provides a critical test of various density functional approximations in the description of bridged d8-d8 metal complexes. The results show that density functional theory calculations can reproduce the primary experimental observations if dispersion interactions are added, and a hybrid functional, which includes exact exchange, is used.

Original languageEnglish
JournalJournal of the American Chemical Society
Volume146
Pages (from-to)13962−13973
ISSN0002-7863
DOIs
Publication statusPublished - 2024

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