Anionic coordination complexes of C60 and C70 with cyclopentadienyl and pentamethylcyclopentadienyl molybdenum dicarbonyl.

Crystalline anionic coordination complexes (PPN(+)){CpMo(CO)2(η(2)-C60)}(-) (), (PPN(+)){CpMo(CO)2(η(2)-C70)}(-)·0.5C6H14 () and (PPN(+)){CpMo(CO)2(η(2)-C60)}(-)·C6H5CN·C6H4Cl2 () containing cyclopentadienyl (, ) and pentamethylcyclopentadienyl () molybdenum dicarbonyl η(2)-coordinated to fullerenes have been obtained by the reaction of the (PPN(+))(fullerene˙(-)) salt with the {Cp()Mo(CO)3(2)}2 dimers (PPN(+) is bis(triphenylphosphoranylidene)ammonium cation). The {CpMo(CO)2(η(2)-C60(70))}(-) anions contain neutral C60 and C70. The optical properties and geometry of the CpMo(CO)2 moieties in and are similar to those in (PPN(+)){CpMo(0)(CO)3}(-). The analysis of optical data for shows that η(2)-coordinated C60 molecules are more negatively charged in than in and . Complexes show weak EPR signals indicating that the major part of the samples is EPR silent and diamagnetic. Diamagnetism of the anions in is explained by the chemical bond formation between the initially paramagnetic CpMo(I)(CO)2 and (fullerene)˙(-) units. The DFT calculations for and support the diamagnetic singlet ground state for both complexes, in which the singlet-triplet energy gaps calculated at the M11/cc-pVTZ-PP/cc-pVDZ level of theory are about 1.27 and 0.95 eV, respectively. According to the calculations, C60 molecules are more negatively charged in than in and that can be explained by stronger back donation from the molybdenum moieties to fullerenes.