Cl-35 and Cl-37 magic-angle spinning NMR spectroscopy in the characterization of inorganic perchlorates

Cl-35 quadrupole coupling constants (C-Q), asymmetry parameters (eta(Q)), a nd isotropic chemical shifts (delta(iso)) have been determined for a series of inorganic perchlorates from Cl-35 magic-angle spinning (MAS) NMR spectr a at 14.1 T. Illustrative Cl-37 MAS NMR spectra are obtained and analyzed f or some of the samples. For perchlorate anions with quadrupolar couplings l ess than about 1 MHz, the Cl-35/Cl-37 NMR parameters are most precisely det ermined from the full manifold of spinning sidebands observed fur the satel lite transitions while line-shape analysis of the central transition is emp loyed for the somewhat larger quadrupolar couplings. The environments for t he individual perchlorate anions are best characterized by the quadrupole c oupling parameters (e.g., C-Q ranges from 0.3 to 3.0 MHz), while the disper sion in the isotropic Cl-35 chemical shifts is small (1029 ppm < delta(iso) < 1049 ppm) for the perchlorates studied. Due to the variation in quadrupo le coupling parameters, Cl-35 MAS NMR may conveniently be employed for iden tification 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 KClO4, RbClO4, CsClO4, (CH3)(4 )NClO4, and the anhydrous and/or hydrated farms of LiClO4, NaClO4, Mg(ClO4) (2), Ba(ClO4)(2), and Cd(ClO4)(2). The Cl-35 MAS NMR spectra of LiClO4, Mg( ClO4)(2), and Ba(ClO4)(2), for which the crystal structures are unknown, re veal that each of these salts possesses a single perchlorate site in the as yInmetric unit. The Cl-35 NMR data for Mg(ClO4)(2) and Ba(ClO4)(2) suggest that these two samples are isostructural. Relationships between the Cl-35 N MR parameters and crystal symmetries are discussed for the other perchlorat es: where crystal structure data have been reported.