Planar pentacoordinate zinc group elements, (M = Zn, Cd, Hg) were computationally found to be at a global minimum in Li5M+ clusters. The stability of these clusters is due to the presence of multicentric bonds. The central element (Zn, Cd, Hg) in each cluster features a negative oxidation state owing to the in-plane electron donation by the Li5 + framework. A similar global minimum planar pentacoordinate structure is found in Na5Zn+ and Na5Cd+ clusters.

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Planar hypercoordinate structures are gaining immense attention due to the shift from common paradigm. Herein, our high level ab initio calculations predict that planar pentacoordinate aluminium and gallium centres in Cu5Al2+ and Cu5Ga2+ clusters are global minima in their singlet ground states. These clusters are thermodynamically and kinetically very stable. Detailed electronic structure analyses reveal the presence of σ-aromaticity which is the driving force for the stability of the planar form.

Quantum chemical calculations were carried out to investigate the nature of the bonding between a neutral Be 3 ring and noble gas atom. Electronic structure calculation for these complexes was carried out at different computational levels in association with natural bond orbital, quantum theory of atoms in molecules, electron localization function, symmetry adapted perturbation theory, and molecular electrostatic potential surface analysis of Be 3 complexes. The Be atoms in the Be 3 moiety are chemically bonded to one another, with the Be Be bond dissociation energy being $125 kJ mol À1 . The Be 3 ring interacts with the noble gases through noncovalent interactions. The binding energies of the noble gas atoms with the Be 3 ring increases with increase in their atomic number. The non-covalent interaction index, density overlap region indicator and independent gradient model analyses reveal the presence of non-covalent inter-fragment interactions in the complexes. Energy decomposition analysis reveals that dispersion plays the major role towards stabilizing these systems.

The multifaceted little Na−B bond in NaBH3‐ cluster has been the subject of many recent studies. Many proposals have been put forward for the complete understanding of the chemical bonding in NaBH3‐ cluster. However, none of the studies provided a complete picture. Herein, the missing recipe of the chemical bonding in NaBH3‐ cluster has been identified which completes the description. Our calculations reveal that the chemical bonding in NaBH3‐ cluster is more multifaceted than ever thought. Our finding suggests that the NaBH3‐ cluster features a Na−B one electron bond which is assisted by three 3‐centre‐2‐electron Na‐B−H bond. Detailed topological analyses of electron density and electron localization function at the correlated level reveal such a bonding situation. This missing 3‐centre‐2‐electron Na‐B−H bond completes the description of chemical bonding in NaBH3‐ cluster which is at‐per with the well established bonding scenario for electron deficient compounds. Similar bonding scenario is observed in KBH3−, CuBH3‐ and AuBH3− clusters, further lending support to the complete picture of bonding.

High level ab initio calculations were carried out to establish the half-sandwich structural behavior of heavier group-14 elements (Si Pb) with neutral Be 3 ring fragment and their molecular hydrogen adsorption capacity. The proposed complexes are found to be global minima on the potential energy surface after a rigorous systematic isomeric search. Quantum chemical investigation revealed that the complexes found possess high bond dissociation energy and also favorable thermodynamics of their formation. The complexes were also found to possess significant aromatic behavior. Among all the complexes, gravimetric density reaches more than the target level by US DOE in case of Be 3 Si and Be 3 Ge system which makes them potential target for molecular H 2 storage. Furthermore, the average adsorption energy, E ad for these two complexes ranges between physisorption and chemisorption process, thereby suggesting their reversible H 2 storage property.aromaticity, Be 3 ring fragment, group-14 elements, H 2 storage, half-sandwich complex | INTRODUCTIONThe origin of half-sandwich complex took place almost parallel to the discovery of ferrocene [1-4] when Fischer and Hafner carried out the synthesis of tetracarbonyl (cyclopentadienyl) vanadium complex, C 5 H 5 V(CO) 4 [5]. Since then, a number of half-sandwich complexes have been predicted and characterized so far [6][7][8][9][10][11][12][13][14][15][16]. Although the library of such complexes containing transition metals is rich, but half-sandwich complexes of main group elements are limited in the literature. Recently our group predicted the half-sandwich behavior of neutral Be 3 ring with some transition metals (Fe, Ru, Os, Zn, Cd, and Hg) [17]. The motive was to incorporate a transition metal two electron donor to neutral Be 3 ring to make the overall system aromatic. Upon complexation with the transition metals, it was found that aromaticity was induced in ring. Now will similar interaction happen with main group elements? To check this, we have chosen heavier group-14 elements (Si Pb) for this study (Scheme 1).The reason for choosing heavier group-14 elements is the presence of documented evidence of them participating in sandwich type complex formation. In 2018, Tholen et al. stabilized Ge (II) by incorporating it into borole dianion which resulted in the formation of a half sandwich complex [18]. Again, Guha et al. carried out high level ab initio calculations to predict a number of half-sandwich complexes between borole dianion and group-14 elements [19]. Further in 2020, Heitkemper and his group published the synthesis and characterization of the first neutral η5-borole complex of Si(II) [20]. The specificity of this complex is the nucleophilic reactivity which can be applied as a Si-centered donor ligand toward transition metals [20]. All of these studied complexes contain group-14 element in their +2 oxidation state as the anionic counterpart made the overall complex neutral.

Density functional calculations have been carried out to investigate the possibility of trapping of noble gas dimers by cyclo[18]carbon dimer. Parallel‐displaced conformation of the cyclo[18]carbon dimer is found to be the minimum energy structure. Noncovalent interaction is found to hold the noble gas dimers. The lighter noble gases (He, Ne) posses weaker attractive interactions while the heavier one (Ar, Kr) are held by stronger attractive interactions forming genuine bonds. Each of the noble gas atoms in turn forms noncovalent interaction with the cyclo[18]carbon monomers. The bond dissociation energy of the noble gas dimers dramatically increases inside the cyclo[18]carbon dimer. Energy decomposition analysis reveals that dispersion plays the major role toward the stabilization energy.

Planar hypercoordinate structures are gaining immense attention due to the shift from common paradigm. Herein, our high level ab initio calculations predict that planar pentacoordinate aluminium and gallium centres in Cu5Al2+ and Cu5Ga2+ clusters are global minima in their singlet ground states. These clusters are thermodynamically and kinetically very stable. Detailed electronic structure analyses reveal the presence of both σ and π aromaticity which is the driving force for the stability of the planar form.