Solid State Nuclear Magnetic Resonance, 1 (1992) 205-210 Elsevier Science Publishers B.V., Amsterdam 205 Magic-angle-spinning 31 P NMR spectra of solid dihydrogen phosphates Comparison of ordered and dynamically disordered compounds Claudia M. Lagier a, Alejandro C. Olivieri a, David C. Apperlcy b and Robin K. Harris b a Departamento de Quimica Analitica, Facultad de Ciencias Bioquimicas y Farmaceuticas, Uniccrsidad Nacional de Rosario, Suipacha 531, Rosario 2000, Argentina b Department of Chemistry and Industrial Research Laboratories, University of Durham, South Road, Durham D1l1 3LE, UK (Received 14 August 1992; accepted 19 August 1992) Abstract High-resolution 31p NMR spectra are reported for several dihydrogen phosphates in the solid state. Shielding tensor components were retrieved by analysis of the sideband intensities. The results, together with previously published data, can be grouped according to the presence and type of proton exchange occurring in the crystals. Static MH zP04 samples (M = Na, Li) show a shielding anisotropy .dO" of - 120 ppm. In the case of M = Cs (one static P-OH bond and two oxygens attached to "half' hydrogens on the average) .dO" is smaller ( - 75 ppm) and can be understood in terms of the accepted, proton-exchange model. For highly disordered samples (M = K, NH 4 , Rb), where all four oxygens have nearby hydrogens with 50% occupancy, .dO" is even smaller (- 30 ppm) but not zero. In the last-mentioned cases, 31 P NMR information suggests that local P0 4 environments may not have the symmetry that could be expected on the basis of the known crystal structures. Keywords: magic-angle-spinning NMR; dihydrogen phosphates; shielding tensors; crystallographic disorder; spinning side- band analysis Introduction The interpretation of 31 P NMR chemical shifts in terms of structural features is of continuing interest [1,2]. Several scientific areas are con- nected with the study of 31 P NMR parameters, from industrially important polyphosphates to model biological compounds. From the structural point of view, interest has been focussed on the Correspondence to: Dr. A.c. Olivieri, Departamento de Quim- ica Analitica, Facultad de Ciencias Bioquimicas y Farmaceuti- cas, Universidad Nacional de Rosario, Suipacha 531, Rosario 2000, Argentina. relation between the 31 P shielding tensor compo- nents in P0 4 groups and P-O bond lengths, via the existence of P-O ..-bonding [3-7]. As is known, tensor components span - 200 ppm, and contain more valuable information than their isotropic counterparts, which are confined to a restricted range of - 20 ppm. Several empirical correlations have been attempted between P-O bond distances and 31 P shielding tensors [4-7]. Attention has been also paid to bond-angle ef- fects [6] and- to the type of groups bonded to the oxygen atoms, that is, whether a given phosphate group belongs to one of the following types: pol-, (RO)POj-, (RO)2POZ or (RO)3 PO, where R = H, alkyl, or another P0 4 unit [7]. In 0926-20-l0/92/S05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved