In addition, Zr12-oleate has a band with the highest wavenumber, 1597 cm -1 . Typically the wavelength difference between ν as (COO) and ν s (COO) is used as a diagnostic tool to distinguish between chelating (∆ν < 110 cm -1 ), bridging (∆ν = 140 -190 cm -1 ) or mondentate (∆ν = 200-320 cm -1 ) binding modes. This is an empirical rule-of-thumb and in case of multiple bands it is difficult to assign the paired ν s (COO). With these limitations in mind, we tentatively calculate ∆ν = 190 cm -1 for the band at 1597 cm -1 , and assign it to the ligands that bridge the two clusters. More importantly, the same ν as (COO) pattern of Zr12oleate is retrieved for all the Zr12 clusters (see also Figure ). Furthermore, the ν as (COO) pattern of Zr6-methylheptanoate is quasi identical to that of Zr6-methylbutanoate. This is an exciting observation since it provides a very fast method to distinguish between the Zr6 and Zr12 clusters.