Normal coordinate analyses for the 24 mixed halogenohexaborates B6XnY6-n2-, n = 1—5, Χ ≠ Y = Cl, Br, I, including the pairs of geometric isomers for n = 2, 3, 4 have been performed, based on a general valence force field. Using the bond lengths and force constants for the homoleptic species B6X62-, which with respect to the B6 cage are weighted standardized, the calculated frequencies are in good agreement with observed IR and Raman bands. The boronhalogen stretching vibrations for symmetric molecular axes correspond with the Ra(IR) bands of the homoleptic compounds: ClB6Cl 327 (515), BrB6Br 207 (430), IB6I 152 (394) cm-1. As a characteristic feature the mixed halogeno clusters exhibit bands with nearly averaged frequencies from asymmetrical axes: ClB6Br 261 (487), ClB6I 227 (473), BrB6I 178 (409) cm-1. This complete vibrational coupling is confirmed by properly balanced potential energy distribution on BX and BY bonds. There is a slight influence of the different substituents on the internal modes of the B6 cage (pseudo-Oh), observed in the sequence A1g>T1u> Eg>T2g in the region 1220-740 cm-1. The bands are shifted about 100 cm-1 with increasing mass of halogen, broadened by boron isotopomers (max. 60 cm-1), and degenerate vibrations are split by lowered point and site symmetry up to 100 cm-1.