In Situ Infrared and Raman Analysis of Structural Changes of (C₆₀Pd₃)_n Coordination Polymer under Elevated Pressure

Structural changes of a fullerene-palladium (C₆₀Pd₃) coordination polymer under increased pressure conditions were monitored via in situ infrared and Raman spectroscopy. The body-centered cubic structure of the fullerene-based coordination polymer could be transferred to the amorphous (C₆₀)_n homofullerene polymeric phase under a mild pressure of ∼4.5 GPa. This phase was formed by C₆₀Pd₃ under considerably milder pressure conditions than C₆₀ polymerization that required higher pressure. Analogous investigations performed with C₆₀[η²-Pd(PPh₃)₂] complex did not form the (C₆₀)_n homofullerene polymeric phase. The transformation of C₆₀Pd₃ to an amorphous homofullerene polymer phase was possibly because of the formation of metallic palladium nanocrystals and a local pressure increase, resulting in the formation of (C₆₀)_n. Additional theoretical calculations showed that pressure strongly influenced the bonding of fullerene moieties in the presence of palladium clusters. This effect was particularly significant in the case of C₆₀ moiety linked through palladium atoms.