Titanium/Yttrium Mixed Metal Nitride Clusterfullerene TiY2N@C80: Synthesis, Isolation, and Effect of the Group-III Metal

Titanium/yttrium mixed metal nitride clusterfullerene (MMNCF) TiY2N@C-80 has been successfully synthesized, representing the first Ti-containing non-scandium MMNCF. TiY2N@C-80 has been isolated by multistep HPLC and characterized by various spectroscopies in combination with DFT computations. The electronic absorption property of TiY2N@C-80 was characterized by UV-vis-NIR spectroscopy, indicating the resemblance to that of TiSc2@C-80 with broad shoulder absorptions. The optical band gap of TiY2N@C-80 (1.39 eV) is very close to that of TiSc2N@C-80 (1.43 eV) but much smaller than that of Y3N@C-80 (I-h, 1.58 eV). Such a resemblance of the overall absorption feature of TiY2N@C-80 to TiSc2N@C-80 suggests that TiY2N@C-80 has a similar electronic configuration to that of TiSc2N@C-80, that is, (TiY2N)(6+)@C-80(6-). FTIR spectroscopic study and DFT calculations accomplish the assignment of the C-80:I-h isomer to the cage structure of TiY2N@C-80, with the C-1 conformer being the lowest energy structure, which is different from the C-s conformer assigned to TiSc2N@C-80. The electrochemical properties of TiY2N@C80 were investigated by cyclic voltammetry, revealing the reversible first oxidation and first reduction step with E-1/2 at 0.00 and -1.13 V, respectively, both of which are more negative than those of TiSc2N@C-80, while the electrochemical energy gap of TiY2N@C80 (1.11 V) is almost the same as that of TiSc2N@C-80 (1.10 V). Contrary to the reversible first reduction step, the second and third reduction steps of TiY2N@C-80 are irreversible, and this redox behavior is dramatically different from that of TiSc2N@C80, which shows three reversible reduction steps, indicating the strong influence of the encaged group-III metal (Y or Sc) on the electronic properties of TiM2N@C-80 (M = Y, Sc).