Fig. 9. Comparison of the CO stretch vibrations of all homoleptic hexacarbonyl complexes known to date. Literature values taken from^13,47 and references therein; E_u/A_2u/T_1u vibrations are IR active (black squares), A_1g and E_g vibrations are Raman active (blue stars and green triangles) note: the methods of measurement of these data differ (e.g. solution/solid state IR); a detailed table can therefore be found in the S.I.‡.