Reversible Self-Assembly of Water-Soluble Gold(I) Complexes

The reaction of the gold polymers containing bipyridyl and terpyridyl units, [Au(C≡CC15H10N3)]n and [Au(C≡CC10H7N2)]n, with the water-soluble phosphines 1,3,5-triaza-7-phosphatricyclo[3.3.1.13.7]decane and 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane gives rise to the formation of four gold(I) alkynyl complexes that self-assemble in water (H2O) and dimethyl sulfoxide (DMSO), through different intermolecular interactions, with an impact on the observed luminescence displayed by the supramolecular assemblies. A detailed analysis carried out by NMR studies performed in different DMSO/deuterated H2O mixtures indicates the presence of two different assembly modes in the aggregates: (i) chain assemblies, which are based mainly on aurophilic interactions, and (ii) stacked assemblies, which are based on Au···π and π···π interactions. These different supramolecular environments can also be detected by their intrinsic optical properties (differences in absorption and emission spectra) and are predicted by the changes in the relative binding energy from density functional theory calculations carried out in DMSO and H2O. Small-angle X-ray scattering (SAXS) experiments performed in the same mixture of solvents are in agreement with the formation of aggregates in all cases. The aromatic units chosen, bipyridine and terpyridine, allow the use of external stimuli to reversibly change the aggregation state of the supramolecular assemblies. Interaction with the Zn2+ cation is observed to disassemble the aggregates, while encapsulating agents competing for Zn2+ complexation revert the process to the aggregation stage, as verified by SAXS and NMR. The adaptive nature of the supramolecular assemblies to the metal-ion content is accompanied by significant changes in the absorption and emission spectra, signaling the aggregation state and also the content on Zn2+. © 2017 American Chemical Society.
The authors are grateful to the Ministry of Economy, Industry and Competitiveness of Spain (AEI/FEDER, UE Projects CTQ2016-76120-P, CTQ2015-65040-P, and CTQ2015-70117-R). This work was also supported by the Associated Laboratory for Sustainable Chemistry, Clean Processes and Technologies, LAQV, which is financed by national funds from FCT/MEC (UID/QUI/50006/2013) and cofinanced by the ERDF under the PT2020 Partnership Agreement (POCI-01-0145-FEDER-007265). The IQAC NMR Facility 500 MHz spectrometer and cryoprobe were funded by the CSIC13-4E-2076 MINECO-FEDER grant. SAXS experiments were performed at the NCD-BL11 beamline of the ALBA Synchrotron Light Facility in collaboration with the ALBA staff. A.J.M. thanks the FCT for a postdoctoral grant (SFRH/ BPD/69210/2010). This research was supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme (to R.G.). We also thank L. Gimeńez and I. Brea for their help on the synthesis of the ligands.