VIBRATIONAL SPECTROSCOPY AT HIGH-PRESSURES .55. THE CRYSTAL-STRUCTURE OF RE(CO)5I, THE VIBRATIONAL-SPECTRA OF THE MANGANESE AND RHENIUM PENTACARBONYL CHLORIDES AND IODIDES, AND THEIR BEHAVIOR UNDER HIGH-PRESSURE

The crystal structure of Re(CO)5I has been determined. The unit-cell symmetry is Cmcm, Z = 4, and differs from the Pnma symmetry of the corresponding chloride and bromide. Low-temperature far-IR and Raman data are reported for M(CO)5X, (M = Mn, Re; X = Cl, I), and assigned by reference to the established assignments of the bromides. Neither Re(CO)5Br nor Re(CO)5I shows a phase change upon compression to 43 kbar, but all the modes harden with increase of pressure. A pressure-induced crossover between A1, nu-6, nu-(Re-I) and E, nu-20, delta-(CReC) was observed and helps to confirm that part of the assignment.