An improved synthetic method has been found for the preparation of the pentamethylcyclopentadienyl rhenium dicarbonyldihalide complexes. From the reaction of (η5-C5Me5)Re(CO)3 with Br2 or I2 in THF-H2O a mixture of cis and trans isomers of (η5-C5Me5)Re(CO)2X2 X = Br and I is formed. On the other hand, the reaction of [(η5-C5Me5)Re(CO)3C1][SbC16] in water gives the cis-(η5-C5Me5)Re(CO)2C12 complex. The solid IR spectra of the dicarbonyldihalide complexes are recorded and an assignment of the normal modes in terms of local symmetry is suggested by comparison with those observed in analogous molecules. A normal coordinate analysis performed using a modified general valence force field and considering simplified models, confirms most of the experimental assignments. The set of valence force constants reflects the structure of the isomers under study.