title: Formation of novel transition metal hydride complexes with ninefold hydrogen coordination.
abstract: Ninefold coordination of hydrogen is very rare, and has been observed in two different hydride complexes comprising rhenium and technetium. Herein, based on a theoretical/experimental approach, we present evidence for the formation of ninefold H- coordination hydride complexes of molybdenum ([MoH9]3-), tungsten ([WH9]3-), niobium ([NbH9]4-) and tantalum ([TaH9]4-) in novel complex transition-metal hydrides, Li5MoH11, Li5WH11, Li6NbH11and Li6TaH11, respectively. All of the synthesized materials are insulated with band gaps of approximately 4 eV, but contain a sufficient amount of hydrogen to cause the H 1s-derived states to reach the Fermi level. Such hydrogen-rich materials might be of interest for high-critical-temperature superconductivity if the gaps close under compression. Furthermore, the hydride complexes exhibit significant rotational motions associated with anharmonic librations at room temperature, which are often discussed in relation to the translational diffusion of cations in alkali-metal dodecahydro-closo-dodecaborates and strongly point to the emergence of a fast lithium conduction even at room temperature.
authors.affiliation: Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Takagi
authors.affiliation: Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Iijima
authors.affiliation: Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
authors.forename: Toyoto
authors.initials: T
authors.lastname: Sato
authors.affiliation: Quantum Beam Science Research Directorate, National Institute for Quantum and Radiological Science and Technology, Hyogo 679-5148, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Saitoh
authors.affiliation: Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba 305-0801, Japan.
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Ikeda
authors.affiliation: Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba 305-0801, Japan.
authors.forename: Toshiya
authors.initials: T
authors.lastname: Otomo
authors.affiliation: Toyota Central R&D Laboratories, Inc., Nagakute 480-1192, Japan.
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Miwa
authors.affiliation: Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
authors.forename: Tamio
authors.initials: T
authors.lastname: Ikeshoji
authors.affiliation: Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.|WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
authors.forename: Shin-Ichi
authors.initials: SI
authors.lastname: Orimo