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Inorganic Chemistry

Star of David catenane shines with both Ir and Zn

Helical, chiral compound first with 2 types of metals

by Leigh Krietsch Boerner
January 8, 2021 | A version of this story appeared in Volume 99, Issue 2


The crystal structure of the Ir-bound catenane.
Credit: J. Am. Chem. Soc.
X-ray crystal structure of one version of the catenane with a hexafluorophosphate ion (peach) bound in the central cavity. C = orange or blue; N = dark blue; O = red; Ir = crimson; Zn = white.

What’s big, star-shaped, and stands out as the first catenane made with two types of metals? A star of David circular helicate complex containing both iridium and zinc. Synthesized by David Leigh and coworkers of the University of Manchester, the compound may lead to new types of photoactive catalysts and sensors (J. Am. Chem. Soc. 2020, DOI: 10.1021/jacs.0c12038). This new complex combines three things for the first time, Leigh says. The molecule can bind anions very tightly in the central cavity close to the Ir atoms, the compound is chiral, and it has interesting photochemical properties. The researchers built the Ir(III)-containing catenane structure stepwise by first strategically binding Ir to phenyl pyridine ligands, Leigh says. Unlike other metals, which tend to pop on and off ligands quickly, the Ir stays bound. Leigh and coworkers separated this mix of chiral diastereomers, stitched together the star of David structure with Zn, and joined the free ends of the ligands via ring-closing metathesis. The group was able to then remove the Zn atoms, leaving these coordination sites available for other metals. By substituting other metals in these binding pockets, scientists can potentially make circular helicates with metals that are otherwise impossible to synthesize there, Leigh says.


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