Transition from free rotation of C70 molecules to static disorder in the molecular C70 complex with covalently linked porphyrin dimers: {(FeIIITPP)2O}·C70

摘要

Fullerene C70 and covalently linked porphyrin (FeIIITPP)2O dimers (TPP: tetraphenylporphyrin) form molecular complex {(FeIIITPP)2O}·C70 (1). Each C70 molecule is sandwiched between two (FeIIITPP)2O dimers and is surrounded by phenyl groups of four other porphyrin dimers. At 295 K, C70 molecules freely rotate about the short axis of the molecule in the ab plane. As a result, the disordered C70 molecules form spheroids flattened at the poles. The rotation of C70 stops near 100 K, resulting in the transition from a tetragonal to a monoclinic unit cell with a four-fold increase in the unit cell volume. In monoclinic phase the C70 molecules are located on the axis which coincides with the short axis of the molecule and passes through the midpointsof two oppositely located 6-6 bonds. Since this position has higher symmetry than the own symmetry of C70, it results in statistic disorder of the C70 molecules between two orientations. It was shown that multiple Van der Waals contacts with a concave FeIIITPP macrocycle which appear below 100 K, play an important role in the ordering of C70.