Probing the stability of the M2(Benzene)3 M = Fe, Co, and Ni structures upon electron attachment (deletion) and solvated iron clusters by benzene molecules: Fe2(Benzene)4

Abstract

Rice-ball (RB) and multiple decker sandwich (MDS) structures of clusters containing transition metal atoms and benzene (Bz) molecules, [M2Bz3]±1 M = Fe, Co, and Ni were studied by means of density functional theory all-electron calculations including dispersion correction as in the BPW91-D2 method. A RB geometry was identified for the ground state (GS) of neutral Fe2Bz3. However, consistent with reported experimental results, RB and MDS structures may occur for the Fe2Bz3− ion. The RB and MDS isomers of Co2Bz3 are degenerate; they have comparable ionization energies; this finding is in agreement with the experimental results, where two isomers were identified also. Experiment and theory suggest that the Co2Bz3− ion has similar geometry, MDS, as the neutral parent. RB and MDS motifs are degenerate for both Ni2Bz3 and Ni2Bz3+. A RB form is predicted for Ni2Bz3−. In the GS of Fe2Bz4 one benzene molecule was found in the outer region of the RB Fe2Bz3 subcluster; it presents a binding energy (D0) of 4.6 kcal/mol, being originated from weak van der Waals forces. Thus, bridging the internal ligands, the fourth molecule has solvent behavior in the singlet Fe2Bz4 GS. Likewise, 3 + 1 MDS isomers of Fe2Bz4 were found at higher energies, ≈ 13.1 kcal/mol, from the GS. In Fe2Bz4−, the RB motif yields the GS with a D0 of 6.7 kcal/mol for the solvent unit. Having a D0 of 9.0 kcal/mol for such moiety the MDS Fe2Bz4− ion is near in energy (3.6 kcal/mol) to the Fe2Bz4− GS. The GS has an electron affinity (EA) of 0.40 eV. Notably, the MDS isomer has a larger EA (0.83 eV). The outer molecule in the 3 + 1 RB GS is stabilized by a network of dipole Cδ−–Hδ+–Cδ− interactions, formed between the external (internal) hydrogen atoms and the π-electrons of the internal (external) benzene rings. Dipole C–Hintδ+–Cextδ− interactions predominate in the 3 + 1 MDS isomers.