35Cl and (37)Cl Magic-Angle Spinning NMR Spectroscopy in the Characterization of Inorganic Perchlorates

35Cl quadrupole coupling constants (C(Q)), asymmetry parameters (eta(Q)), and isotropic chemical shifts (delta(iso)) have been determined for a series of inorganic perchlorates from (35)Cl magic-angle spinning (MAS) NMR spectra at 14.1 T. Illustrative (37)Cl MAS NMR spectra are obtained and analyzed for some of the samples. For perchlorate anions with quadrupolar couplings less than about 1 MHz, the (35)Cl/(37)Cl NMR parameters are most precisely determined from the full manifold of spinning sidebands observed for the satellite transitions while line-shape analysis of the central transition is employed for the somewhat larger quadrupolar couplings. The environments for the individual perchlorate anions are best characterized by the quadrupole coupling parameters (e.g., C(Q) ranges from 0.3 to 3.0 MHz), while the dispersion in the isotropic (35)Cl chemical shifts is small (1029 ppm < delta(iso) < 1049 ppm) for the perchlorates studied. Due to the variation in quadrupole coupling parameters, (35)Cl MAS NMR may conveniently be employed for identification of anhydrous and hydrated phases of perchlorates, in studies of phase transitions, hydration reactions, and the composition of mixed phases. The perchlorates studied include anhydrous KClO(4), RbClO(4), CsClO(4), (CH(3))(4)NClO(4), and the anhydrous and/or hydrated forms of LiClO(4), NaClO(4), Mg(ClO(4))(2), Ba(ClO(4))(2), and Cd(ClO(4))(2). The (35)Cl MAS NMR spectra of LiClO(4), Mg(ClO(4))(2), and Ba(ClO(4))(2), for which the crystal structures are unknown, reveal that each of these salts possesses a single perchlorate site in the asymmetric unit. The (35)Cl NMR data for Mg(ClO(4))(2) and Ba(ClO(4))(2) suggest that these two samples are isostructural. Relationships between the (35)Cl NMR parameters and crystal symmetries are discussed for the other perchlorates where crystal structure data have been reported.