Planar Hypercoordinate Carbons in Alkali Metal Decorated CE₃²⁻ and CE₂²⁻ Dianions

Abstract

After exploring the potential energy surfaces of M m CE 2 p (E=SÀ Te, M=LiÀ Cs, m = 2, 3 and p = m-2) and M n CE 3 q (E=SÀ Te, M=LiÀ Cs, n = 1, 2, q = n-2) combinations, we introduce 38 new global minima containing a planar hypercoordinate carbon atom (24 with a planar tetracoordinate carbon and 14 with a planar pentacoordinate carbon). These exotic clusters result from the decoration of V-shaped CE 2 2À and Y-shaped CE 3 2À dianions, respectively, with alkali counterions. All these 38 systems fulfill the geometrical and electronic criteria to be considered as true planar hypercoordinate carbon systems. Chemical bonding analyses indicate that carbon is covalently bonded to chalcogens and ionically connected to alkali metals.

Why an integrated approach between search algorithms and chemical intuition is necessary?

“…It is important to note that AUTOMATON is a program that uses a probabilistic cellular automated method to generate the initial population, which then evolves through genetic operations. This method has been designed to identify the global minimum, assessing its efficiency in different systems, 41 with recent application to design global minima with planar hypercoordinate carbons, [49][50][51][52] organic dications, 53 deltahedral Zintl clusters, 54 among others. 55,56 Our initial search yielded 1450 different geometries.…”

Strong carbon – noble gas covalent bond and fluxionality in hypercoordinate compounds

“…20 These compounds, in conjunction with those hypercoordinated carbon systems, have been studied extensively because of the breaking of the traditional rules that indicate that carbon should form four covalent bonds in a tetrahedral arrangement. [21][22][23][24][25][26][27][28][29] However, to the authors' knowledge, no systematic study of hypercoordinated carbon compounds containing C-Ng s-bonds has been reported to date. The only hypercoordinated compound containing a noble gas atom was reported by Olah and coworkers, who predicted the structure and dissociation in the CH 4 2+ and He components.…”

Revisiting the potential-energy surface of CnBe3n+2H2n+22+ (n = 2–4) clusters: are planar pentacoordinate carbon structures the global minima?

“…The literature reports numerous ptC, 51 ppC, and only 15 planar hexacoordinate carbon (phC) GM structures. 14,[16][17][18][19][20] However, the effectiveness of search algorithms diminishes with the system size due to the exponential increase in the number of minima to visit. Besides, the search process often requires computationally expensive local optimization methods, such as density functional theory (DFT) or ab initio.…”

“…Our group implemented and used the AUTO-MATON program, 21 an evolutive algorithm, to identify many GM with p-hyp-Cs (ptCs, ppCs, and phCs). 7,9,10,18,19,22,23 Other frequently used programs are the CALYPSO (Crystal structure AnaLYsis by Particle Swarm Optimization) package [24][25][26] and the coalescence kick (CK) stochastic method implementations. 27,28 In addition to identifying the GM and other relevant isomers, it is essential to analyze the kinetic stability and whether the p-hyp-Cs species maintain their chemical identity in the oligomers they form.…”