Fulleride-metal η5 sandwich and multi-decker sandwich complexes: A DFT prediction.

Abstract

The (C60 CN)- 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, (C60 CN)- , 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 (C60 CN)- 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 -(C60 CN)- )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 -(C60 CN)- )2 ] compared to ferrocene. The energy of dissociation (ΔE) of the ligand (C60 CN)- from [Fe(η5 -(C60 CN)- )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 (C60 CN)- 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.