A VARIABLE-TEMPERATURE STUDY OF RU-3(CO)(12) IN THE SOLID-STATE AND THE GENERATION OF ALTERNATIVE CRYSTAL-STRUCTURES

The molecular and crystal structure of Ru-3(CO)(12) has been reinvesti gated on single-crystal X-ray diffraction data collected at 100 and 15 0 K. Thermal motion analysis on high-order diffraction data have been used to characterize the motion about equilibrium positions of the mol ecule as a whole and of groups of atoms. It has been shown that, while the molecule undergoes an almost isotropic rigid-body librational and translational motion, the three Ru(CO)(4) units undergo different lib rational motions about the axes passing between each Ru atom and bisec ting the opposite Ru-Ru bond. Packing potential energy calculations an d computer graphics have been used to show that the most favoured pack ing motion the experimental crystal is based on interlocking between t etracarbonyl units formed by two pairs of CO ligands at right angles a long a Ru-Ru edge. Starting from the structure of Ru-3(CO)(12), altern ative crystal arrangements have been generated and compared with the e xperimental crystal structure in terms of packing efficiency and cohes ive energy.