Synthesis and Characterisation of Helicate and Mesocate Forms of a Double-Stranded Diruthenium(ii) Complex of a Di(terpyridine) Ligand
Kate L. Flint A , J. Grant Collins B , Siobhan J. Bradley C , Trevor A. Smith C , Christopher J. Sumby A and F. Richard Keene A DA Department of Chemistry, School of Physical Sciences, The University of Adelaide, Adelaide, SA 5005, Australia.
B School of Physical, Environmental and Mathematical Sciences, UNSW Canberra, Australian Defence Force Academy, Canberra, ACT 2600, Australia.
C ARC Centre of Excellence in Exciton Science, School of Chemistry, The University of Melbourne, Vic. 3010, Australia.
D Corresponding author. Email: richard.keene@adelaide.edu.au
Australian Journal of Chemistry 72(10) 762-768 https://doi.org/10.1071/CH19220
Submitted: 13 May 2019 Accepted: 30 May 2019 Published: 1 July 2019
Abstract
A diruthenium(ii) complex involving the di(terpyridine) ligand 1,2-bis{5-(5″-methyl-2,2′:6′,2″-terpyridinyl)}ethane was synthesised by heating an equimolar ratio of RuCl3 and the ligand under reflux conditions in ethylene glycol for 3 days, realising double-stranded helicate and mesocate forms which were chromatographically separated. The two species were obtained in relatively low yield (each ~7–9 %) from the reaction mixture. X-Ray structural studies revealed differences in the cavity sizes of the two structures, with the helicate structure having a significantly smaller cavity. Furthermore, the helicate and mesocate forms pack with notably different arrangements of the structures with the helicate having large solvent and anion filled pores. 1D/2D NMR studies revealed rigidity in the mesocate structure relative to that of the helicate, such that the –CH2CH2– signal was split in the former and appeared as a singlet in the latter. In a manner analogous to the behaviour of the parent [Ru(tpy)2]2+ coordination moiety (tpy = 2,2′:6′,2″-terpyridine), photophysical studies indicated that both the helicate and mesocate forms were non-emissive at ~610 nm at room temperature, but at 77 K in n-butyronitrile, both isomers showed emission at ~610 nm (λex 472 nm). However, the temporal emission characteristics were very different: time-resolved studies showed the emission of the helicate species decayed with a dominant emission lifetime of ~10 μs (similar to the emissive properties of free [Ru(tpy)2]2+ under the same conditions), whereas for the mesocate the emission lifetime was at least three orders of magnitude lower (~4 ns).
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