The Existence of a Designer Al=Al Double Bond in the LiAl₂H₄⁻ Cluster Formed by Electronic Transmutation

Abstract

The Al=Al double bond is elusive in chemistry. Herein we report the results obtained via combined photoelectron spectroscopy and ab initio studies of the LiAl H cluster that confirm the formation of a conventional Al=Al double bond. Comprehensive searches for the most stable structures of the LiAl H cluster have shown that the global minimum isomer I possesses a geometric structure which resembles that of Si H , demonstrating a successful example of the transmutation of Al atoms into Si atoms by electron donation. Theoretical simulations of the photoelectron spectrum discovered the coexistence of two isomers in the ion beam, including the one with the Al=Al double bond.

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

“…For example, the LiAlH 4 and LiBH 4 salts are currently commerciallya vailable, and they can be viewed as SiH 4 and CH 4 analogues. We think the large-scale synthesis of Li n Al n H 2n + 2 ,L i n B n H 2n + 2 and Li n Al n H 2n can come true soons ince Li 2 Al 3 H 8 À [8] and LiAl 2 H 4 À [9] are observed in the gas phase through the recombination of the plasma generated from the laser vaporization of LiAlH 4 powder.…”

“…A stable neutral compound with an Al=Al double bond was synthesized by Inoue and co‐workers using bulky ligands very recently . For the gas phase study, the designed ion is LiAl 2 H 4 − , which was generated and characterized with the same methods as Li 2 Al 3 H 8 − . The measured anion photoelectron spectrum of LiAl 2 H 4 − is presented in Figure A, and three EBE bands were observed (X, X′ and X“), among which X belongs to the global minimum Isomer I, X′ and X” belong to the second lowest lying Isomer II (Figure B).…”

“…As table neutralc ompound with an Al=Al double bond was synthesized by Inoue and co-workers using bulky ligands very recently. [46] For the gas phase study,t he designed ion is LiAl 2 H 4 À , [9] which was generated and characterizedw ith the same methods as Li 2 Al 3 H 8 À .T he measured anion photoelectron spectrum of LiAl 2 H 4 À is presented in Figure 6A,a nd three EBE bands were observed (X, X' and X"), among which X belongs to the globalm inimum Isomer I, X' and X" belong to the second lowest lying IsomerII( Figure 6B). The next question is whether the Al=Al double bond exists in the global minimum structure IsomerI?A dNDP analysis showni nF igure 6C presentst wo 2c-2e s-AlÀHb onds (ON = 2.00 j e j), two 3c-2e s-Li-H-Al bonds (ON = 1.97 j e j)( these four bonds are analogoust ot he s-SiÀHb onds in Si 2 H 4 ), one s-3c-2e Al-Li-Al bond (ON = 1.99 j e j)( an analogue of the s-SiÀSi bond in Si 2 H 4 ), and one p-AlÀAl bond (ON = 2.00 j e j)( an analogue of the p-SiÀSi bond in Si 2 H 4 ).…”

“…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.…”