Unusually Short Be−Be Distances with and without a Bond in Be₂F₂and in the Molecular Discuses Be₂B₈and Be₂B₇⁻

Abstract

Quantum-chemical calculations at the CCSD(T)/cc-pVTZ level of theory show that beryllium subfluoride, Be2 F2 , has a bond dissociation energy of De =76.9 kcal mol(-1) , which sets a record for the strongest Be-Be bond. The synthesis of this molecule should thus be possible in a low-temperature matrix. The discus-shaped species Be2 B8 and Be2 B7 (-) possess the shortest Be-Be distance for a molecule in the electronic ground state, but there is no Be-Be bond. The cyclic species Be2 B8 and Be2 B7 (-) exhibit double aromaticity with 6σ and 6π electrons, which strongly bind the Be2 fragment to the boron atoms. The very short interatomic distance between the beryllium atoms is due to the Be-B σ and π bonds, which operate like spokes in a wheel pressing the beryllium atoms together. The formation of the Be-B bonds has effectively removed the electronic charge of the valence space between the beryllium atoms. Along the Be-Be axis, there are two cage critical points adjacent to a ring critical point at the midpoint, but there is no bond critical point and no bond path.

A Very Short Be–Be Distance but No Bond: Synthesis and Bonding Analysis of Ng–Be2O2–Ng′ (Ng, Ng′=Ne, Ar, Kr, Xe)

“…A stable molecule that possesses a shorter interatomic distance than a double bond without chemical bonding is, to our knowledge, unprecedented. Such a possibility was recently reported by two of us in a theoretical study of the experimentally still unknown discus‐shaped species Be 2 B 8 and Be 2 B 7 − , which were calculated with Be−Be distances between 1.901–1.910 Å . The observed compounds Ng−Be 2 O 2 −Ng′ have much shorter Be−Be distances.…”

“…Table shows that the bond order P(Be−Be) has a value of 0.08 in all complexes Ng−Be 2 O 2 −Ng′. This is much smaller than in diatomic Be 2 which has a calculated equilibrium distance of 2.534 Å (experimentally 2.453 Å) but a bond order of 0.38 . The very polar Be−O bonds in the complexes Ng−Be 2 O 2 −Ng′ have a uniform bond order of P(Be−O)=0.54.…”

Dynamic Mg2B8 Cluster: A Nanoscale Compass

“…To locate the global minimum (GM) of Mg 2 B 8 , we performed global searches using the Coalescence Kick (CK) algorithm . Our choice of the present system benefits from two prior computational studies on relevant binary clusters, although dynamic fluxionality is either not recognized or not possible in those systems . For the Mg 2 B 8 cluster in this work, a total of 3000 stationary points were probed on the potential energy surface in the CK global searches.…”

“…It is 0.23 eV higher in energy at single‐point CCSD(T), suggesting that the GM is reasonably well‐defined. The energetics of C s versus D 8 h isomers in Mg 2 B 8 and its isovalent Be 2 B 8 species is an interesting issue, which leads to the favorable C s structure for Mg 2 B 8 but not for Be 2 B 8 (Figure ), the latter cluster being thus nonfluxional.…”

Boron Nanowheels with Axles Containing Noble Gas Atoms: Viable Noble Gas Bound M©B10−Clusters (M=Nb, Ta)

“…They include [Ta 2 B 6 ] −/0 , M 2 B n ( n =6–10; M=Sc, Ti, V), and Fe 2 B n ( n =6–9) . Recently, Frenking and co‐workers noted that Be 2 B 7 − and Be 2 B 8 clusters also adopt inverse sandwich‐like geometries. However, Ng‐supported inverse sandwiches are unprecedented.…”