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

Heterometallic coordination polymers of Au(I) and Ag(I) with 6-thioguanosine, poly( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mo>[</mml:mo> <mml:msub><mml:mi>Au</mml:mi> <mml:mi>x</mml:mi></mml:msub> <mml:msub><mml:mi>Ag</mml:mi> <mml:mrow><mml:mn>1</mml:mn> <mml:mo>-</mml:mo> <mml:mi>x</mml:mi></mml:mrow> </mml:msub> <mml:mrow><mml:mo>(</mml:mo> <mml:mn>6</mml:mn></mml:mrow> <mml:mo>-</mml:mo> <mml:mrow><mml:mi>tG</mml:mi> <mml:mo>)</mml:mo></mml:mrow> <mml:mo>]</mml:mo></mml:mrow> <mml:annotation>${[{\rm{Au}}_{\rm{x}} {\rm{Ag}}_{1 - x} {\rm{(6}} - {\rm{tG)}}]}$</mml:annotation> </mml:semantics> </mml:math> ), 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>λ</mml:mi> <mml:mo>></mml:mo> <mml:mn>300</mml:mn></mml:mrow> <mml:annotation>${\lambda \char62 300}$</mml:annotation> </mml:semantics> </mml:math> nm which can be interpolated in a linear manner between x <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mo>=</mml:mo> <mml:mn>0</mml:mn> <mml:mo>.</mml:mo> <mml:mn>0</mml:mn></mml:mrow> <mml:annotation>${ = 0.0}$</mml:annotation> </mml:semantics> </mml:math> and x <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mo>=</mml:mo> <mml:mn>1</mml:mn> <mml:mo>.</mml:mo> <mml:mn>0</mml:mn></mml:mrow> <mml:annotation>${ = 1.0}$</mml:annotation> </mml:semantics> </mml:math> 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.