The electronic structure of potassium intercalated Tm@C82

We present studies of the electronic structure of the potassium intercalated endohedral monometallofullerene Tm@C82 using photoemission spectroscopy. Upon intercalation we find evidence for at least two additional stable phases: an intermediate phase K3Tm@C82 which forms a face centered molecular crystal and a final compound K6Tm@C82 with a body centered structure. From valence band photoemission we observe that upon intercalation the unoccupied states are subsequently filled with potassium 4s electrons ending up with a charge transfer of eight electrons on the C82 cage. The valency of the Tm ions does not change to values bigger than two upon the intercalation process. For none of the intermediate potassium concentations metallic phases are observed.