  We present the single-crystalline x-ray diffraction study on the Ba4Ru3O10
consisting of the corner-shared Ru3O12 trimers. The crystal structure is
re-determined from 78 to 300 K across an antiferromagnetic transition at 105 K.
The orthorhombic symmetry (Cmca, space group No. 64) is preserved at all
temperatures measured. This structure presents exceptionally long Ru-O
distances characterized by a significant distribution within the Ru3O12 trimer.
A bond valence sum calculation suggests that the charge disproportionation
within the Ru3O12 trimer emerges even at room temperature, which we ascribe to
molecular orbital formation in the Ru3O12 trimer, as supported by recent
theoretical calculations. Based on the analyzed crystal structure, the
electronic states and the nature of the phase transition at 105 K are
discussed.

Strongly Correlated Electrons