Figure : FTIR spectra of Zr12-acetate, -propionate, -hexanoate, -oleate and Zr6methylheptanoate. The weak band at 1750 cm -1 in the spectrum of Zr12-acetate is assigned to a small amount of acetic acid that is not involved in hydrogen bonding of any kind. An ester impurity is ruled out because of the absence of any signal around 4 ppm in NMR, (see Figure ).