Molecules in clusters: the case of planar LiBeBCNOF built from a triangular form LiOB and a linear four-center species FBeCN

TL;DR

This study combines high-level quantum chemistry calculations to analyze the structure of a cluster molecule, revealing how its components interact and confirming previous DFT-based predictions of its lowest-energy isomer.

Contribution

It provides detailed CCSD and RHF calculations of the cluster's fragments, offering new insights into their geometries and interactions, and validates DFT results with more accurate methods.

Findings

LiOB is accurately characterized as a triangular molecule.

FBeCN is confirmed to be linear in isolation.

Interaction causes FBeCN to become bent within the cluster.

Abstract

Krueger some years ago proposed a cluster LiBeBCNOF, now called periodane. His ground-state isomer proposal has recently been refined by Bera et al. using DFT. Here, we take the approach of molecules in such a cluster as starting point. We first study therefore the triangular molecule LiOB by coupled cluster theory (CCSD) and thereby specify accurately its equilibrium geometry in free space. The second fragment we consider is FBeCN, but treated now by restricted Hartree-Fock (RHF) theory. This four-center species is found to be linear, and the bond lengths are obtained from both RHF and CCSD calculations. Finally, we bring these two entities together and find that while LiOB remains largely intact, FBeCN becomes bent by the interaction with LiOB. Hartree-Fock and CCSD theories then predict precisely the same lowest isomer found by Bera et al. solely on the basis of DFT.