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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

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Publication details

The article was received on 24 Jul 2018, accepted on 05 Oct 2018 and first published on 08 Oct 2018


Article type: Edge Article
DOI: 10.1039/C8SC03258K
Citation: Chem. Sci., 2018, Advance Article
  • Open access: Creative Commons BY-NC license
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    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., 2018, Advance Article , DOI: 10.1039/C8SC03258K

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