Molecular Structure and Magnetic and Optical Properties of Endometallonitridofullerene Sc3 N@Ih -C80 in Neutral, Radical Anion, and Dimeric Anionic Forms.

Abstract

A series of compounds with Sc3 N@Ih -C80 in the neutral, monomeric, and dimeric anion states have been prepared in the crystalline form and their molecular structures and optical and magnetic properties have been studied. The neutral Sc3 N@Ih -C80 ⋅3 C6 H4 Cl2 (1) and (Sc3 N@Ih -C80 )3 (TPC)2 ⋅5 C6 H4 Cl2 (2, TPC=triptycene) compounds both crystallized in a high-symmetry trigonal structure. The reduction of Sc3 N@Ih -C80 to the radical anion resulted in dimerization to form diamagnetic singly bonded (Sc3 N@Ih -C80 - )2 dimers. In contrast to {[2.2.2]cryptand(Na+ )}2 (Sc3 N@Ih -C80 - )2 ⋅2.5 C6 H4 Cl2 (3) with strongly disordered components, we synthesized new dimeric phases {[2.2.2]cryptand- (K+ )}2 (Sc3 N@Ih -C80 - )2 ⋅2 C6 H4 Cl2 (4) and {[2.2.2]cryptand- (Cs+ )}2 (Sc3 N@Ih -C80 - )2 ⋅2 C6 H4 Cl2 (5) in which only one major dimer orientation was found. The thermal stability of the (Sc3 N@Ih -C80 - )2 dimers was studied by EPR analysis of 3 to show their dissociation in the 400-460 K range producing monomeric Sc3 N@Ih -C80 .- radical anions. This species shows an EPR signal with a hyperfine splitting of 5.8 mT. The energy of the intercage C-C bond was estimated to be 234±7 kJ mol-1 , the highest value among negatively charged fullerene dimers. The EPR spectra of crystalline (Bu3 MeP+ )3 (Sc3 N@Ih -C80 .- )3 ⋅C6 H4 Cl2 (6) are presented for the first time. The salt shows an asymmetric EPR signal, which could be fitted by three lines. Two lines were attributed to Sc3 N@Ih -C80 .- . Hyperfine splitting is manifested above 180 K due to the hyperfine interaction of the electron spin with the three scandium atoms (a total of 22 lines with an average splitting of 5.32 mT are observed at 220 K). Furthermore, each of the 22 lines is additionally split into six lines with an average separation of 0.82 mT. The large splitting indicates intrinsic charge and spin density transfer from the fullerene cage to the Sc3 N cluster. Both the monomeric and dimeric Sc3 N@Ih -C80 - anions show an intrinsic shift of the IR bands attributed to the Sc3 N cluster and new bands corresponding to these species appear in the NIR range of their UV/Vis/NIR spectra, which allows these anions to be distinguished from neutral species.