title: True boundary for the formation of homoleptic transition-metal hydride complexes.
abstract: Despite many exploratory studies over the past several decades, the presently known transition metals that form homoleptic transition-metal hydride complexes are limited to the Groups 7-12. Here we present evidence for the formation of Mg3 CrH8 , containing the first Group 6 hydride complex [CrH7 ](5-) . Our theoretical calculations reveal that pentagonal-bipyramidal H coordination allows the formation of σ-bonds between H and Cr. The results are strongly supported by neutron diffraction and IR spectroscopic measurements. Given that the Group 3-5 elements favor ionic/metallic bonding with H, along with the current results, the true boundary for the formation of homoleptic transition-metal hydride complexes should be between Group 5 and 6. As the H coordination number generally tends to increase with decreasing atomic number of transition metals, the revised boundary suggests high potential for further discovery of hydrogen-rich materials that are of both technological and fundamental interest.
authors.affiliation: Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan).
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Takagi
authors.forename: Yuki
authors.initials: Y
authors.lastname: Iijima
authors.forename: Toyoto
authors.initials: T
authors.lastname: Sato
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Saitoh
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Ikeda
authors.forename: Toshiya
authors.initials: T
authors.lastname: Otomo
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Miwa
authors.forename: Tamio
authors.initials: T
authors.lastname: Ikeshoji
authors.forename: Katsutoshi
authors.initials: K
authors.lastname: Aoki
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Orimo
keywords: chromium; hydride ligands; hydrides; structure elucidations; transition metals