Varying the Alkali-Metal Radii in (K_xRb_1–x)_n[GaH₂]_n (0 ≤ x ≤ 1) Reorients a Stable Polyethylene-Structured [GaH₂]_n^n– Anionic Chain

Abstract

The stability of a negatively charged polyethylene-structured [GaH2]n(n-) cluster ion was investigated by varying the K(+)/Rb(+) ratio in ((K(x)Rb(1-x))n[GaH2]n (0 ≤ x ≤ 1). Neutron, X-ray, and IR spectroscopies were used to characterize the new phases. Between the limiting compositions Kn[GaH2]n and Rbn[GaH2]n, the [GaH2]n(n-) chains remained almost identical, indicating a stable specie. For rubidium-rich samples up to a potassium content corresponding to (K0.5Rb0.5)n[GaH2]n, two phases coexist in the samples, RbGaH2 and (K0.5Rb0.5)n[GaH2]n, with a ratio mirroring the relative alkali-ion content. The two phases have a different alignment of the [GaH2]n(n-) chains. For potassium-rich samples beyond (K0.5Rb0.5)n[GaH2]n, the samples were single-phased. The unit cell volume of the new (K0.5Rb0.5)n[GaH2]n structure type shrinks according to Vegard's law as smaller K(+) ions substitute for larger Rb(+) ions. The [GaH2]n(n-) chains remained, however, almost identical. IR spectra from the different phases were very similar, exhibited stretching, scissoring, and rocking modes similar to those in ordinary polyethylene, but shifted to lower frequencies, reflecting weaker Ga-H bonds. The existence of stable Kn[GaH2]n and Rbn[GaH2]n, would help to dehydrogenate KGaH4 and RbGaH4 upon heating. If this could be transferred to lighter alanates and borohydrides, it could be possible to develop more functional hydrogen-storage systems.

Electronic Transmutation (ET): Chemically Turning One Element into Another

“…Germanium hydrides (germanes), even though not in a large scale, have been synthesized and shown hydrocarbon‐like structures . The ET of gallium into germanium enjoys fruitful experimental discoveries . Powders of gallium hydride (gallane)‐containing compounds, such as Cs 10 H[(Ga 3 H 8 ) 3− ] 3 , (K x Rb 1− x ) n [(GaH 2 ) ‐ ] n , Rb 8 [Ga(GaH 3 ) 4 5− ] and Rb n [(GaH 2 ) − ] n have been synthesized and characterized by X‐ray diffraction, where K, Rb and Cs are used as the electron donors.…”

“…In Cs 10 H[(Ga 3 H 8 ) 3− ] 3 , both ET and the Zintl–Klemm concept are utilized to design the compound, and the (Ga 3 H 8 ) 3− kernel is isostructural to propane and Ge 3 H 8 . In (K x Rb 1− x ) n [(GaH 2 ) − ] n and Rb n [(GaH 2 ) − ] n , the [(GaH 2 ) − ] n polyanions feature polyethylene structures, and in Rb 8 [Ga(GaH 3 ) 4 5− ], the Ga(GaH 3 ) 4 5− kernel has similar structure as neopentane. In all these examples, each of the Ga atoms obtain one negative charge for the electronic transmutation.…”

“…[49] The ET of gallium into germanium enjoys fruitful experimentald iscoveries. [10][11][12] Powders of gallium hydride (gallane)-containing compounds, such as Cs 10 H[(Ga 3 H 8 ) 3À ] 3 , (K x Rb 1Àx ) n [(GaH 2 ) -] n ,R b 8 [Ga(GaH 3 ) 4 5À ]a nd Rb n [(GaH 2 ) À ] n have been synthesized and characterized by X-ray diffraction, where K, Rb and Cs are used as the electrond onors. In Cs 10 H[(Ga 3 H 8 ) 3À ] 3 , [10] both ET and the Zintl-Klemm concept [50] are utilized to design the compound, and the (Ga 3 H 8 ) 3À kernel is isostructural to propanea nd Ge 3 H 8 .I n( K x Rb 1Àx ) n [(GaH 2 ) À ] n [11] and Rb n [(GaH 2 ) À ] n , [12] the [(GaH 2 ) À ] n polyanions feature polyethylene structures, and in Rb 8 [Ga(GaH 3 ) 4 5À ], [12] the Ga(GaH 3 ) 4 5À kernel has similars tructure as neopentane.…”

“…The similarities between the transmutated element Z and the targeted element Z+1 could range from the chemical bonding they possess to the geometries of the compounds they form, so that many key features that were thought only belong to element Z+1 can now belong to element Z. Alchemists once spent great efforts in transmutating common elements into precious others, which now we know is not possible merely with chemistry, but based on ET, the element Z can now be chemically “turned into” element Z+1. After the proposal of the ET concept, a plethora of successful examples, including the transmutation of Groups 13, 14, and 15 elements into Group 14, 15, and 16 elements, have been reported . In this Minireview, we will summarize these examples on both the theoretical and experimental fronts, and outlook for wider applications and future research directions of this new concept.…”

“…After the proposal of the ET concept, ap lethora of successful examples, including the transmutation of Groups 13, 14, and 15 elements into Group 14,15, and 16 elements, have been reported. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] In this Minireview,w ewill summarize these exam-ples on both the theoretical and experimental fronts, and outlook for wider applicationsa nd future research directions of this new concept.…”