Dalton Transactions PAPER Cite this: Dalton Trans., 2016, 45, 12846 Received 27th April 2016, Accepted 22nd July 2016 DOI: 10.1039/c6dt01643j www.rsc.org/dalton π-Stacking attraction vs. electrostatic repulsion: competing supramolecular interactions in a tpphz-bridged Ru(II)/Au(III) complex† Dieter Sorsche, a Markus Schaub, a Frank W. Heinemann, b Johannes Habermehl, a Susanne Kuhri, c Dirk Guldi, d Julien Guthmuller e and Sven Rau* a The synthesis and characterization of a mixed metal ruthenium(II)/gold(III) complex bridged by tetrapyrido- phenazine (tpphz) are described. It is isostructural and isoelectronic to the well-known photocatalysts with palladium(II) or platinum(II). Concentration dependent 1 H-NMR spectroscopy and XRD studies show that the electrostatic repulsion between the gold(III) moieties exceeds the attractive π-stacking interaction. Theoretical calculations based on the new structural data confirm an increased positive charge on the bridging ligand as well as significantly altered orbital symmetry as compared to the previously investigated palladium(II) complex. This is the first example of a tpphz ruthenium(II) complex where π-stacking is com- pletely inhibited. The detailed investigation of the solid-state structure showed for the first time in bi- metallic tpphz bridged complexes no significant torsion within the bridging ligand itself. Although catalytic performance for proton reduction by gold(III) is naturally not observed, its photochemical decomposition in colloidal gold particles could be shown by TEM and DLS. Introduction Recent studies on the photocatalytic hydrogen evolution using photochemical molecular devices (PMD) based on tpphz- bridged dinuclear ruthenium/d 8 metal catalysts (tpphz = tetra- pyrido[3,2-a:2′,3′-c:3″,2″-h:2′′′,3′′′-j ]phenazine) have shown that π-stacking interactions between the large aromatic scaffold of the bridge significantly influence the catalytic activity. 1–3 Tack- ling this issue, it was shown that the activity of a tpphz-bridged ruthenium/palladium catalyst could be enhanced by the addition of an electron-rich organic π-system, i.e. pyrene or anthracene, as they build π-stacked assemblies with the catalyst complex and therefore inhibit dimerization. 4,5 In this study, a solid-state structure of the [(tbbpy) 2 Ru(tpphz)PdCl 2 ] 2+ catalyst with a polyoxometallate (POM) as the counter-ion has been reported. A bending of the tpphz towards the POM indicated that electrostatic interactions between the positively charged ruthenium(II) and palladium(II) centers and the four-fold anionic cluster play a significant role in the intermolecular assembly. However, theoretical calculations on the electron transfer processes during catalysis were based on a planar model of the dinuclear PMD. 3,6,7 Therefore, it was highly desir- able to obtain further model structures. Generally, replacing the catalyst metal by gold(III) adds an additional charge to the system while retaining the coordination environment and, hence, provides an isostructural and isoelectronic model complex with respect to the literature known photocatalysts (Scheme 1). Square-planar phenanthroline gold(III) complexes have been shown to be potent intercalators in DNA, which in combination with the chromophore gives rise to potential appli- cations in photodynamic therapy. 8–12 The heterodinuclear complex containing a photoreductive ruthenium chromophore and gold(III) can be further envisaged as a precursor for the for- mation of gold(0) particles or clusters by visible light. Results and discussion Synthesis Bis(4,4′-di-tert-butyl-2,2′-bipyridine-κ 2 N 1 ,N 1′ ) ruthenium(2+) [(tetra- pyrido[3,2-a:2′,3′-c:3″,2″-h:2′′′,3′′′-j ]phenazine-κN 4 ,κN 5 ) hexa- † Electronic supplementary information (ESI) available: Concentration depen- dent 1 H-NMR spectra, DLS results, and TEM images, ESP maps, and calculated excited states. CCDC 1452865 and 1452866. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6dt01643j a Institute for Inorganic Chemistry I, Ulm University, Albert-Einstein-Allee 11, D-89081 Ulm, Germany. E-mail: sven.rau@uni-ulm.de b Institute of Inorganic and General Chemistry, Egerlandstr. 1, D-91058 Erlangen, Germany c Institute of Energy and Climate Research, Electrochemical Process Engineering (IEK-3), Wilhelm-Johnen-Straße, D-52428 Jülich, Germany d Friedrich-Alexander-Universität Erlangen/Nürnberg, Department Chemie und Pharmazie, Lehrstuhl für Physikalische Chemie I, Egerlandstraße 3, D-91058 Erlangen, Germany e Faculty of Applied Physics and Mathematics, Gdansk University of Technology, Narutowicza 11/12, 80-233 Gdansk, Poland 12846 | Dalton Trans. , 2016, 45, 12846–12853 This journal is © The Royal Society of Chemistry 2016 Published on 22 July 2016. Downloaded by Universitat Erlangen Nurnberg on 03/01/2018 13:59:50. View Article Online View Journal | View Issue