Hybrid layered double perovskite (HLDP) halides comprise hexa-coordinated 1+ and 3+ metals in the octahedral sites within a perovskite layer and organic amine cations between the layers. Progress on such materials has hitherto been limited to compounds containing main group 3+ ions isoelectronic with Pb II (such as Sb III and Bi III ). Here, we report eight HLDP halides from the A2M I M III X8 family, where A = para-phenylenediammonium (PPDA), 1,4-butanediammonium (1,4-BDA) or 1,3propanediammonium (1,3-PDA); M I = Cu or Ag; M III = Ru or Mo; X = Cl or Br. The optical band gaps, which lie in the range 1.55 eV to 2.05 eV, are tunable according to the layer composition, but are largely independent of the spacer. Magnetic measurements carried out for (PPDA)2Ag I Ru III Cl8 and (PPDA)2Ag I Mo III Cl8 show no obvious evidence of a magnetic ordering transition. While the t2g 3 Mo III compound displays Curie-Weiss behavior for a spin-only d 3 ion, the t2g 5 Ru III compound displays marked deviations from the Kotani theory. ASSOCIATED CONTENT Supporting InformationSynthesis and characterization, scXRD refinement details, key bond lengths and bond angles, hydrogen bond interactions, power x-ray diffraction patterns, x-ray photoelectron spectra (XPS), scanning electron microscope (SEM) images, additional single-crystal x-ray structures, octahedral tilting Accession CodesCCDC (2122532 -2122540) contain the supplement crystallographic data for this paper which can be obtained free of charge via www.ccdc.cam.ac.uk

Nanocomposites formed by carboxyl-functionalized MoS2 nanotubes with poly­(diallyldimethylammonium chloride) (PDDA, described as P)-modified single-walled carbon nanotubes (SWCNT) and borocarbonitride nanotubes (BCNNT) have been prepared by a solution-phase flocculation of 1D nanotubes. The nanocomposites show higher photocatalytic and electrocatalytic HER activities compare to the individual constituents, where the H2 yield improves with the MoS2 nanotube proportion. The maximum H2 evolution rate achieved is 7475 μmol g–1 h–1 in the nanocomposite of MoS2–P.SWCNT with a MoS2–P.SWCNT proportion of 3:1, whereas the corresponding physical mixture exhibits only 3112 μmol g–1 h–1. The MoS2–P.SWCNT (3:1) nanocomposite also shows superior electrocatalytic H2 evolution with an onset potential of 80 mV (vs RHE). The MoS2–P.BCNNT composite exhibits a somewhat lower H2 evolution rate. Electrostatic stacking of 1D MoS2 nanotubes with SWCNT/BCNNT appears to be a valuable strategy for HER and related catalytic reactions.

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Halide double perovskites are a promising class of semiconducting materials for applications in solar cells and other optoelectronic devices. Recently, there has been a surge of interest in these materials...

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