PREPARATION, VIBRATIONAL-SPECTRA, AND NOR MAL-COORDINATE ANALYSIS OF BROMO-IODO-RHENATES(IV), [REBRNI6-N](2-), N=0-6

The IR and Raman spectra of the ten bromo-iodo-rhenates(IV) [ReBrnI6-n ](2-), n = 0-6, including the geometrical isomers for n = 2,3,4, have been recorded at 80 K. The vibrational spectra are completely assigned according to point groups O-h, D-4h, C-4v, C-3v, and C-2v, as support ed by normal coordinate analyses based on a general valence force fiel d. Due to the different trans-influences Br < I in asymmetric axes Br' -Re-I', the Re-I' bonds are strengthened and the Re-Br' bonds are weak ened, as indicated by valence force constants, for Re-I' on average 8, 5% higher and for Os-Br' 8,3% lower, as compared with the values calcu lated for symmetric I-Re-I and Br-Re-Br axes, respectively.