Fulleride-metal η 5 sandwich and multi-decker sandwich complexes: A DFT prediction.

The (C 60 CN) - formed by the reaction of CN - with fullerene shows high electron rich character, very similar to C 60 ˙ - , and it behaves as a large anion. Similar to Cp - , the bulky anion, (C 60 CN) - , acts as a strong η 5 ligand towards transition metal centers. Previous studies on η 5 coordination of fullerene cage are reported for pseudo fullerenes whereas the present study deals with sandwich complexes of (C 60 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(η 5 -(C 60 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(η 5 -(C 60 CN) - ) 2 ] compared to ferrocene. The energy of dissociation (ΔE) of the ligand (C 60 CN) - from [Fe(η 5 -(C 60 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 (C 60 CN) - ligand behaved as one of the bulkiest ligands in the chemistry of sandwich complexes. Further, the coordinating ability of the dianion, (C 60 (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.