Abstract
We have explored the chemical space of BAl4Mg−/0/+ for the first time and theoretically characterized several isomers with interesting bonding patterns. We have used chemical intuition and a cluster building method based on the tabu-search algorithm implemented in the Python program for aggregation and reaction (PyAR) to obtain the maximum number of possible stationary points. The global minimum geometries for the anion (1a) and cation (1c) contain a planar tetracoordinate boron (ptB) atom, whereas the global minimum geometry for the neutral (1n) exhibits a planar pentacoordinate boron (ppB) atom. The low-lying isomers of the anion (2a) and cation (3c) also contain a ppB atom. The low-lying isomer of the neutral (2n) exhibits a ptB atom. Ab initio molecular dynamics simulations carried out at 298 K for 2000 fs suggest that all isomers are kinetically stable, except the cation 3c. Simulations carried out at low temperatures (100 and 200 K) for 2000 fs predict that even 3c is kinetically stable, which contains a ppB atom. Various bonding analyses (NBO, AdNDP, AIM, etc.) are carried out for these six different geometries of BAl4Mg−/0/+ to understand the bonding patterns. Based on these results, we conclude that ptB/ppB scenarios are prevalent in these systems. Compared to the carbon counter-part, CAl4Mg−, here the anion (BAl4Mg−) obeys the 18 valence electron rule, as B has one electron fewer than C. However, the neutral and cation species break the rule with 17 and 16 valence electrons, respectively. The electron affinity (EA) of BAl4Mg is slightly higher (2.15 eV) than the electron affinity of CAl4Mg (2.05 eV). Based on the EA value, it is believed that these molecules can be identified in the gas phase. All the ptB/ppB isomers exhibit π/σ double aromaticity. Energy decomposition analysis predicts that the interaction between BAl4−/0/+ and Mg is ionic in all these six systems.
Highlights
IntroductionFrom the time that the concept of planar tetracoordinate carbon (ptC) emerged [1,2], it was extended to its group elements (Si, Ge, Sn, etc.) [3,4,5,6,7,8,9,10] and to other elements such as B [11,12,13,14,15,16,17], Al [18,19], N [20,21,22], P [23], O [24], and lately even to the
There are two main reasons why experimentalists [5,6,26,27,28,29,30,31,32,33] and theoreticians [2,34,35,36,37,38,39,40,41,42,43] have put a great deal of effort into studying these special class of molecules: (i) planar tetracoordinate carbon (ptC) is a fundamental deviation from the conventional ideas of tetrahedral tetracoordinate carbon [44,45]; (ii) no two structural isomers behave in the same way chemically
ZPVEcorrected relative energies obtained at the ωB97XD/6-311++G(2d,2p) and UωB97XD/6-311++G(2d,2p) levels are given for each geometry
Summary
From the time that the concept of planar tetracoordinate carbon (ptC) emerged [1,2], it was extended to its group elements (Si, Ge, Sn, etc.) [3,4,5,6,7,8,9,10] and to other elements such as B [11,12,13,14,15,16,17], Al [18,19], N [20,21,22], P [23], O [24], and lately even to the. (i) ptC is a fundamental deviation from the conventional ideas of tetrahedral tetracoordinate carbon [44,45]; (ii) no two structural isomers behave in the same way chemically. Making this new class of molecules enhances our existing understanding about chemical bonding, and one could potentially make new materials. The idea of planar tetracoordinate boron (ptB) arrived as a byproduct of stabilizing the ptC itself. ZPVE-corrected relative energies are given in kcal mol−1
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