The formation of closely packed fullerene structures in η2-coordination Ni0(Me3P)3(η2-fullerene) complexes of C60 and C70

Abstract

New reduction method for preparation of coordination fullerene complexes is developed. NiII(Me3P)2Cl2 reduction with sodium amalgam in N,N′-dimethylformamide produces reduction products whose interaction with fullerenes C60 and C70 produces coordination complexes which have been crystallized as Ni(Me3P)3(η2-C60) (1) and Ni(Me3P)3(η2-C70) (2) by slow mixing with n-hexane. Due to small size of the Me3P ligands at nickel atoms complexes have dense packing of fullerene units in a crystal with 3D hexagonal arrangement of C60 and 18 short interfullerene C⋅⋅⋅C contacts for each C60 in 1, and the C70 layers with four fullerene neighbors and 13 short interfullerene C⋅⋅⋅C contacts for each C70 in 2. Nickel atom is coordinated to the 6-6 bond of C60 in 1 or the bond adjacent to two hexagons of C70 in 2 with essential elongation of these bonds in comparison with the average values. The length of the NiC(fullerene) bonds is 2.015–2.055(8) Å. The Me3P ligands coordinate asymmetrically to the nickel atoms in 2 with two short (2.195(2) Å) and one longer (2.278(2) Å) NiP bond. According to the optical data, 1 and 2 are molecular complexes containing Ni0 in the electron configuration d10 and neutral fullerenes. Nevertheless, low-energy charge transfer (CT) bands observed at 748 nm (1) and 884 nm (2) are associated with the metal-to-fullerene CT to show the existence of closely lying excited ionic states.