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Chemists triple down on metal helicates

Combining a multidentate ligand with various metals leads to triple-stranded complexes with potentially useful magnetic properties

by Stephen K. Ritter
October 9, 2017 | A version of this story appeared in Volume 95, Issue 40

Credit: Inorg. Chem.
A diagram shows formation of an iron-zinc-copper triple helicate complex.
Credit: Inorg. Chem.

Chemists have come far in using metal-assisted self-assembly of organic building blocks to construct molecules with three-dimensional architectures. For example, a team led by supramolecular chemistry specialists Pradyut Ghosh of the Indian Association for the Cultivation of Science and Christoph A. Schalley of Free University of Berlin has been matching various metal salts with a multidentate ligand it developed that is made up of a 2,2'-bipyridine core flanked by triazolyl-pyridine groups. This combination leads to formation of unusual trimetallic triple-stranded helicate complexes, (L3M3)6+, where L is the ligand and M is Fe, Co, Ni, Cu, or Zn or a combination of two of the metals. In continuing the work, the team has now systematically used electrospray ionization mass spectrometry to study the formation mechanism and thermodynamic stabilities of the helicates when mixtures of metals are used. The researchers have found that some metals outcompete others for binding sites, leading some of the helicates to be interconverted into others. In one case, they observed formation of (L3FeZnCu)6+ (shown), the first example of such a complex containing three different metals. However, this trinuclear species only appears as an intermediate on the way to (L3Cu3)6+, which is the most stable isolable helicate (Inorg. Chem. 2017, DOI: 10.1021/acs.inorgchem.7b01980). Ghosh and Schalley say the magnetic properties of the trimetallic helicates will be of interest for developing smart materials, in particular for the versions having a combination of diamagnetic and paramagnetic metals.


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