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Issue 1, 2019

Direct observation of the intermediate in an ultrafast isomerization

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Abstract

Using a combination of two-dimensional infrared (2D IR) and variable temperature Fourier transform infrared (FTIR) spectroscopies the rapid structural isomerization of a five-coordinate ruthenium complex is investigated. In methylene chloride, three exchanging isomers were observed: (1) square pyramidal equatorial, (1); (2) trigonal bipyramidal, (0); and (3) square pyramidal apical, (2). Exchange between 1 and 0 was found to be an endergonic process (ΔH = 0.84 (0.08) kcal mol−1, ΔS = 0.6 (0.4) eu) with an isomerization time constant of 4.3 (1.5) picoseconds (ps, 10−12 s). Exchange between 0 and 2 however was found to be exergonic (ΔH = −2.18 (0.06) kcal mol−1, ΔS = −5.3 (0.3) eu) and rate limiting with an isomerization time constant of 6.3 (1.6) ps. The trigonal bipyramidal complex was found to be an intermediate, with an activation barrier of 2.2 (0.2) kcal mol−1 and 2.4 (0.2) kcal mol−1 relative to the equatorial and apical square pyramidal isomers respectively. This study provides direct validation of the mechanism of Berry pseudorotation – the pairwise exchange of ligands in a five-coordinate complex – a process that was first described over fifty years ago. This study also clearly demonstrates that the rate of pseudorotation approaches the frequency of molecular vibrations.

Graphical abstract: Direct observation of the intermediate in an ultrafast isomerization

Supplementary files

Article information


Submitted
24 Jul 2018
Accepted
05 Oct 2018
First published
08 Oct 2018

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2019,10, 113-117
Article type
Edge Article

Direct observation of the intermediate in an ultrafast isomerization

Tyler M. Porter, J. Wang, Y. Li, B. Xiang, C. Salsman, J. S. Miller, W. Xiong and C. P. Kubiak, Chem. Sci., 2019, 10, 113 DOI: 10.1039/C8SC03258K

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