Vibrational spectroscopy at high pressures. The crystal structure of Re(CO)5I, the vibrational spectra of the manganese and rhenium pentacarbonyl chlorides and iodides, and their behaviour under high pressure

Abstract

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, ν₆, ν(Re—I) and E, ν₂₀, δ(CReC) was observed and helps to confirm that part of the assignment.