Rice-ball structures of iron–benzene clusters, Fe4–(C6H6)m, m ⩽ 3. A density functional study

Abstract Geometrical rice-ball structures of the Fe 4 cluster with capped adsorbed benzene molecules for neutral, anion, and cation species, Fe 4 –(C 6 H 6 ) m ( m  ⩽ 3), are studied by means of all-electron calculations done with the BPW91 approach of density functional theory jointly with 6-311++G(2d, 2p) basis sets. Electronic properties like ionization energies and electron affinities as well as binding energies are estimated and are in good agreement with recently reported experimental results. The computed IR spectra for these species show vibrational bands near those of the isolated benzene molecule and some forbidden IR modes of this ligand become IR active in Fe 4 –(C 6 H 6 ) m ( m  ⩽ 3). The metal-benzene bonding issue was studied through the contour plots of molecular orbitals, showing signatures of metal–carbon bonding, originated from the 3d electrons of Fe 4 and the 2pπ electrons of benzene.