Fulleride‐metal η 5 Sandwich and Multi‐decker Sandwich Complexes: A DFT Prediction

Abstract

The (C60CN)− formed by the reaction of CN− with fullerene shows high electron rich character, very similar to C60˙−, and it behaves as a large anion. Similar to Cp−, the bulky anion, (C60CN)−, acts as a strong η5 ligand towards transition metal centers. Previous studies on η5 coordination of fullerene cage are reported for pseudo fullerenes whereas the present study deals with sandwich complexes of (C60CN)− with Fe(II), Ru(II), Cr(II), Mo(II), and Ni(II) and multi-decker sandwich complexes of CN–fullerides with Fe(II). The structural parameters of these complexes and the corresponding Cp− complexes showed very close resemblance. Analysis of the metal-to-carbon bonding molecular orbitals showed that sandwich complex [Fe(η5-(C60CN)−)2] exhibit bonding features very similar to that of ferrocene. Also, a 6-fold decrease in the band gap energy is observed for [Fe(η5-(C60CN)−)2] compared to ferrocene. The energy of dissociation (ΔE) of the ligand (C60CN)− from [Fe(η5-(C60CN)−)2] is slightly lower than the ΔE of a Cp* ligand from a ferrocene derivative wherein each cyclopentadienyl unit is substituted with four tertiary butyl groups. The (C60CN)− ligand behaved as one of the bulkiest ligands in the chemistry of sandwich complexes. Further, the coordinating ability of the dianion, (C60(CN)2)2− is evaluated which showed strong coordination ability simultaneously with two metal centers leading to the formation of multi-decker sandwich and pearl-necklace type polymeric structures.