Characterization of a new hexasodium diphosphopentamolybdate hydrate, Na-6[P2Mo5O23]center dot 7H(2)O, by Na-23 MQMAS NMR spectroscopy and X-ray powder diffraction

A novel hexasodium disphosphopentamolybdate hydrate, Na-6[P2Mo5O23]. 7H(2)O , has been identified using X-ray powder diffraction, H-1, Na-23, and P-31 magic-angle spinning (MAS) NMR, and Na-23 multiple-quantum (MQ) MAS Nh IR. Powder XRD reveals that the hydrate belongs to the triclinic spacegroup P ( 1) over bar with cell dimensions a = 10.090(3) Angstrom, b = 15.348(5) Angs trom, c = 8.460(4) Angstrom, alpha = 101.45(6)degrees, beta = 103.09(2)degr ees, gamma = 90.71(5)degrees, and Z = 2. The number of water molecules of c rystallization has been determined on the basis of a quantitative evaluatio n of the H-1 MAS NMR spectrum, the crystallographic unit cell volume, and a hydrogen content analysis. The Na-23 MQMAS NMR spectra of Na-6[P2Mo5O23]. 7H(2)O, obtained at three different magnetic fields, clearly resolve resona nces from six different sodium sites and allow a determination of the secon d-order quadrupolar effect parameters and isotropic chemical shifts for the individual resonances. These data are used to determine the quadrupole cou pling parameters (C-Q and eta(Q)) from simulations of the complex line shap es of the central transitions, observed in Na-23 MAS NMR spectra at the thr ee magnetic fields. This analysis illustrates the advantages of combining M QMAS and MAS NMR at moderate and high magnetic fields for a precise determi nation of quadrupole coupling parameters and isotropic chemical shifts for multiple sodium sites in inorganic systems. P-31 MAS NMR demonstrates the p resence of two distinct P sites in the asymmetric unit of Na-6[P(2)Mo(5)O23 ]. 7H(2)O while the P-31 chemical shielding anisotropy parameters, determin ed for this hydrate and for Na-6[P(2)Mo(5)O23]. 13H(2)O, show that these tw o hydrates can easily he distinguished using P-31 MAS NMR.