COMPARATIVE MULTINUCLEAR (CL-35, BR-79, BR-81, I-127 AND O-17) MAGNETIC-RESONANCE STUDY OF THE PERHALATE ANIONS XO(4)(-) (X=CL, BR OR I) INACETONITRILE SOLUTION

The NMR spectra (Cl-35, Br-79, Br-81, I-127 and O-17) of the tetrahedr al perhalate anions XO(4)(-) (X = Cl, Br and I) were compared for the first time in acetonitrile solution, a medium in which the resonances are relatively sharp and in which no oxygen exchange occurs. Relaxatio n studies of the quadrupolar nuclei in these solutions at 24 degrees C are reported and show that excellent spectra may be obtained at 0.1 M concentration; thus the observation of separate resonances for (ClO4- )-O-16 and (ClOO3-)-O-18-O-16 represents the first reported instance o f a Cl-35 secondary isotopic shift [(1) Delta(35)Cl(O-18,O-16) = -0.09 0 ppm]. Enrichment with O-17 of all three ions was carried out and the (1)J(I-127,O-17) coupling constant (489 Hz) has been observed for the first time. The chemical shifts and coupling constants are discussed. especially in connection with the anomalous properties of the perbrom ate ion. Halogen chemical shifts for BrO3F, IF7 and IF6+ AsF6- are rep orted for the first time.