# Metal Exchange in Thioguanosine Coordination Polymers of Gold (I) and Silver (I)

## TL;DR

Gold and silver ions form helical polymers with 6-thioguanosine, and these polymers can exchange metals over time, forming new structures.

## Contribution

The discovery that homopolymers of gold and silver with 6-thioguanosine can exchange metals to form heterometallic polymers.

## Key findings

- The composition of the heterometallic polymer matches the mole fractions of the metals in the solution.
- Metal-ligand bonds are labile, allowing metal exchange in about 5 hours at room temperature.
- Heterometallic polymers form helical structures with complex supramolecular behavior.

## Abstract

Heterometallic coordination polymers of Au(I) and Ag(I) with 6‐thioguanosine, poly([AuxAg1-x(6-tG)]
), have been prepared and were observed to form hydrogels. We find that the composition of the heterometallic polymer is proportional to the mole fractions of the metals in the preparation solution. Optical absorption spectra show single peaks for λ>300
nm which can be interpolated in a linear manner between x =0.0
and x =1.0
consistent with the formation of a heterometallic polymer rather than a mixture of homopolymers. However photoluminescence and circular dichroism spectra are sensitive to the supramolecular structure of the polymers and show more complex behaviour. Atomic force microscopy indicated that the molecular chains of the Au homopolymer entwine to form strands that are predominantly right‐hand helices. The Ag homopolymer has previously been shown to form left‐hand helices. Intermediate compositions have more complex structures because of the competition between the left and right‐handed preferences of the homopolymers. Finally, we have shown that the metal‐ligand bonds are labile on a timescale of about 5 h at ambient temperature (about 293 K). Mixtures of homopolymers transform to the corresponding heterometallic coordination polymer by metal exchange as judged by optical absorption, photoluminescence and circular dichroism spectra.

Gold(I) and silver (I) ions react with 6‐thioguanosine to form helical coordination polymers with metal‐sulfur chains. These polymers have a helical structure and show strong circular dichroism and photoluminescence. Mixtures of metal ions result in heterometallic coordination polymers. Further, mixtures of homopolymers will exchange metal ions over about 5 h to produce the corresponding heterometallic polymer at equilibrium.