BAl4Mg−/0/+: Global Minima with a Planar Tetracoordinate or Hypercoordinate Boron Atom

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.

Nanoclusters and nanoalloys of group 13 elements (B, Al, and Ga): benchmarking of methods and analysis of their structures and energies

“…S14, ESI †). A similar geometry involving a p/s dual aromatic planar-pentacoordinate B (ppB) was reported recently, where one of the Al is replaced by Mg. 98 BAl 4 has a kite-like structure with a planar tetra coordinate boron (ptB) at the center.…”

CB6Al0/+: Planar hexacoordinate boron (phB) in the global minimum structure

“…34 Recently, Khatun et al studied the PES of BAl 4 Mg À/0/+ systems and found that the anionic and cationic states of the system have planar tetracoordinate boron (ptB) and the neutral state has a ppB atom in the global minima. 35 The ptB and the ppB structures were reported as kinetically stable and exhibit p/s double aromaticity. In 2001, Minkin and coworkers designed BB 6 (CH) 3 and BB 6 X 2 À (X = NH and O) systems having a planar hexacoordinate boron (phB) atom at both ab initio and DFT level computations.…”

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

“…39 However, this approach is computationally quite expensive for larger elemental compositions like C 12 O 2 Mg 2 . Of course, from our previous studies of small clusters such as CAl 4 Mg −/0 64 and BAl 4 Mg −/0/+ , 65 we realized that it does not guarantee all possible low-lying isomers although global minimum can be found unequivocally.…”

“…Another strategy developed by some of the authors is to build the molecules bottom-up starting from a single atom by adding the remaining atoms sequentially searching for local minima at each stage and using those minima to grow the molecule up to the desired composition. 39 However, this approach is computationally quite expensive for larger elemental Of course, from our previous studies of small clusters such as CAl 4 Mg À/064 and BAl 4 Mg À/0/+ , 65 we realized that it does not guarantee all possible low-lying isomers although global minimum can be found unequivocally.…”