Molecular and crystal structures of decamethylruthenocene (η5-C5Me5)2Ru in the temperature range 153-300 K:: Thermal motion in a crystal according to X-ray diffraction data

The crystal structure of decamethylruthenocene (eta(5)-C5Me5)(2)Ru (1) is investigated by X-ray diffraction. It is demonstrated that the compound studied crystallizes in two polymorphic modifications, namely, modification Ia with space group P2(l)/m (Z=2) in the temperature range 153-300 K and modification Ib with space group P2(l)/n (Z = 4) at 203 K. No temperature phase transition between the modifications is found. In crystal la, the molecule occupies a special position in the mirror plane. In crystal Ib, the molecule is located in the general position. The cyclic ligands eta(5)-C5Me5, (Cp*) are aligned parallel to each other and adopt an eclipsed conformation. The bond lengths in compounds la and Ib are identical. Analysis of the anisotropic displacement parameters of the atoms indicates that molecules la and Ib are not structurally rigid and that the Cp* rings involved in these molecules can execute independent librations. In the temperature range 153-300 K, the Cp*(1) ligand in molecule la is statically disordered over two positions. The barrier heights B-5 for rotation of the Cp* ligands are estimated both from the root-mean-square amplitudes of librations <phi(2)> and with the use of the atom-atom potential method. (C) 2003 MAIK "Nauka/Interperiodica".