Hydroxylated buckminsterfullerene complexes with endohedral europium atom.

The Eu@C60(OH)30 and Eu@C60(OH)20endo-structures were predicted by the (U)DFT quantum chemical method. The arrangement of hydroxyl groups corresponds to the arrangement of chlorine atoms in (D3d)-C60Cl30 and fluorine atoms in (D5d)-C60F20. The calculated squares of the electron spin ‹Ŝ2› were reproduced with high accuracy by the addition of the spins belonging to two unpaired valence electrons and 4f7 subsystem. The total spin multiplicity of the quasi-degenerate ground state is 2·2·8. Some of its 32 components can be distinguished by the IR spectrum. The europium avoids benzoid cycles. It is located asymmetrically within the [18]trannulene cycle in the Eu@C60(OH)30 complex and between a peripheral carbon atoms of the corannulene fragments in the Eu@C60(OH)20 complex. The value ‹Ŝ2› ≈ 16.75 a. u., calculated with MS = 7/2, is key number. It allows limiting the DFT study to only one spin component out of 32 possible components. In contrast with Eu@C60(OH)30 and Eu@C60(OH)20, the Eu@C60 has two quasi-degenerate endohedral spin-tautomers. The (C3v) tautomer includes the hexagonal pyramid EuC6 formed as a result of endohedral η6-bonding of the europium with cyclohexa-1,3,5-triene fragment of buckminsterfullerene. It was obtained for the low-spin and high-spin components of the quasi-degenerate state with the total multiplicity 3·8. The (C2v) tautomer includes a triangular EuC2 fragment and was obtained for the octet spin state. The energy difference of the spin-tautomers is small, but the difference in its IR spectra is very large. [ABSTRACT FROM AUTHOR]