Quantum chemical study of atomic structure evolution of co _x/C₆₀ (x ≤ 2.8) composites

The main features of the local atomic structure of novel Co _x/C₆₀ (x ≤ 2.8) complex mixtures were studied using the ab initio B3LYP/6-31G* method for a set of low- and high-energy Co _n(C₆₀)_m (n = 1, 2, m = 2, 3) clusters in low and intermediate spin states. For the n = 1 isomers the spin state S = 1/2 is energetically preferable, whereas the low-energy isomers of n = 2 have an intermediate spin state of S = 1. The η² (6-6 edge of C ₆₀) type of cobalt ion coordination is preferable for both the n = 1 and n = 2 cases. The η² (coordination with a 6-5 edge) and even the η⁵ (C₅ fragment) types can serve as low- and high-energy intermediates for the cobalt ions migration around the C ₆₀ cage. Formation of cobalt dimers can be the final stage of evolution of Co_x/C₆₀ atomic structure approaching the equilibrium atomic geometry.