Two crystalline modifications of RuO4

RuO4 was prepared by oxidation of elemental ruthenium. Two different modifications were obtained and investigated by X-ray single crystal diffraction. RuO4-I has cubic symmetry image, and two independent tetrahedral molecules are present in the unit cell. Within the standard uncertainties in both molecules the distances Ru–O are 1.695 Å. The second modification, RuO4-II, is monoclinic image and isotypic with OsO4. There is one independent molecule in the unit cell, which shows distances Ru–O of 1.697 and 1.701 Å, respectively.