Chemistry

The ternary fulleride, Rb[Formula: see text]Cs[Formula: see text]C[Formula: see text], is the most expanded member of the family of face-centered cubic (fcc) structured superconducting fullerides ever accessed with superconductivity surviving at ambient pressure closest to the Mott insulator boundary. Here, we study the evolution of its structural and electronic properties with temperature. At ambient temperature, Rb[Formula: see text]Cs[Formula: see text]C[Formula: see text] lies in the Mott–Jahn–Teller (MJT) insulating part of the phase diagram. High-resolution synchrotron X-ray diffraction shows that its structure remains strictly cubic at all temperatures, but the transition to the metallic state at [Formula: see text] 50 K — evident in the evolution of the magnetic susceptibility with temperature — is accompanied by a lattice collapse, [Formula: see text]V/V0 of [Formula: see text]. Bulk superconductivity then emerges on further cooling with a T[Formula: see text] of 25.9 K. Th...

Abstract: The synthesis of novel, monocationic iridiumACHTUNGTRENUNG(III) photosensitisers (Ir-PSs) with the general formula [IrIII(C^N)2(N^N)]+ (C^N: cyclometallating phenylpyridine ligand, N^N: neutral bidentate ligand) is described. The structures obtained were examined by cyclic voltammetry, UV/Vis and photoluminescence spectroscopy and X-ray analysis. All iridium complexes were tested for their ability as photosensitisers to promote homogeneously catalysed hydrogen generation from water. In the presence of [HNEt3]- ACHTUNGTRENUNG[HFe3(CO)11] as a water-reduction catalyst (WRC) and triethylamine as a sacrificial reductant (SR), seven of the new iridium complexes showed activity. [Ir(6-iPr-bpy)ACHTUNGTRENUNG(ppy)2]PF6 (bpy: 2,2’-bipyridine, ppy: 2-phenylpyridine) turned out to be the most efficient photosensitiser. This complex was also tested in combination with other WRCs based on rhodium, platinum, cobalt and manganese. In all cases, significant hydrogen evolution took place. Maximum turnover numbers of 4550 for this Ir-PS and 2770 for the Fe WRC generated in situ from [HNEt3]ACHTUNGTRENUNG[HFe3(CO)11] and trisACHTUNGTRENUNG[3,5-bis(trifluoromethyl)phenyl]- phosphine was obtained. These are the highest overall efficiencies for any Ir/ Fe water-reduction system reported to date. The incident photon to hydrogen yield reaches 16.4% with the best system. Keywords: hydrogen · iridium · iron · photochemistry · photosensitizers · water splitting [a] F. Grtner, Dr. S. Losse, A. Boddien, Dr. G. Anilkumar, Dr. H. Junge, Dr. T. Schulz, Dr. N. Marquet, Dr. A. Spannenberg, Prof. Dr. M. Beller Leibniz-Institut fr Katalyse e.V. Albert-Einstein-Straße 29a, 18059 Rostock (Germany) Fax: (+49) 381-1281-5000 E-mail: [email protected] [b] Dr. D. Cozzula, Prof. Dr. S. Gladiali Universit di Sassari, Dipartimento di Chimica Via Vienna 2, 07100 Sassari (Italy) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201100235. Figure 1. Reaction principle of a water-reduction cascade with an iridium photosensitiser (Ir-PS), a water-reduction catalyst (WRC) and a sacrificial reductant (SR).  2011