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, Li6NbH11 and 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.

Stabilization and electronic topological transition of hydrogen-rich metal Li5MoH11 under high pressures from first-principles predictions

“…Li + , H − , and the ninefold-hydrogen-coordinated [MoH 9 ] . The structure was also predicted in theory to exhibit an insulator–metal transition under compression 21 . As for Li 5 MoH 11 , it was revealed that the P6 3 cm structure transforms into the Cc and Pc structures at 5 GPa and 94 GPa, respectively 21 .…”

“…The structure was also predicted in theory to exhibit an insulator–metal transition under compression 21 . As for Li 5 MoH 11 , it was revealed that the P6 3 cm structure transforms into the Cc and Pc structures at 5 GPa and 94 GPa, respectively 21 . Not long ago an experimental study utilizing high-pressure synchrotron x-ray diffraction (XRD) cast doubt on the ambiguity in structural determination of this ternary compound.…”

“…However, the ternary hydride Li 5 MoH 11 does not at all exhibit high-temperature superconductivity under high pressure, only with its maximum of 6.5 K at 160 GPa belonging to the high-pressure phase 20 . Li 5 MoH 11 being one of the family of the hydrogen-rich metals Li 5 MH 11 , where M = Mo, W, Nb, and Ta 21 , adopts a hexagonal structure with the P6 3 cm space group at ambient pressure, which is constructed via the ionic bonds of i . e .…”

New Phase in Fluid Hydrogen at Room Temperature

“…Another important thing to understand about the properties of H 2 is to comprehend the effects of H 2 on its surroundings. For example, hydrogenation of various metals [10][11][12] , and their metal hydrides [13][14][15] have been studied even under high pressure. High pressure accelerates hydrogenation, which can lead to results in a short time.…”

Hydrogen‐Release Reaction of a Complex Transition Metal Hydride with Covalently Bound Hydrogen and Hydride Ions

“…Although complex anions composed of non‐transition metals and hydrogen such as [BH 4 ] − have been known, the transition metals allow the formation of a greater variety of complex anions. The variety of transition metal hydride complexes is fundamentally interesting and has the potential in a wide range of applications due to their connection to other desirable material properties, such as superconductivity and their ability to store hydrogen . For these reasons, complex transition metal hydrides have been continually studied.…”