Solid State Nuclear Mugnetic Resonance, 1 (1992) 73-83 Elsevier Science Publishers B.V.. Amsterdam 73 Dipolar 31P NMR spectroscopy of crystalline inorganic phosphorus compounds David Lathrop, Deanna Franke, Robert Maxwell, Thomas Tepe, Robert Flesher, Zhengming Zhang and Hellmut Eckert zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA &pcrr.fmerif zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA of Chrmistry, Uric ,ersity of’ California, Sarm Barbartr. C.-l Y.?lOb, USA (Received 20 January 1992; accepted 23 January 1991) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGF Abstract The ability of the 90”-t,-180” pulse sequence to produce accurate dipole-dipole coupling information in solids is investigated. To this end, the experimental “P spin echo decays are measured for eighteen crystalline phosphides and phosphorus chalcogenides and compared with simulations, based on the known internuclear distances in these compounds. The experimental results are generally found accurate in compounds where the dominant contribution to the dipole-dipole coupling arises from nuclei in structurally inequivalent sites with large chemical shift anisotropies. For this situation, the quantum mechanical “flip-flop“ term in the dipolar Hamiltonian is suppressed and the dipole-dipole coupling is entirely heteronuclear in character. All of those compounds that do not obey this condition show accelerated spin echo decays due to a fractional contribution of the flip-flop term and possibly incomplete refocusing of chemical shift terms on the time scale of the experiment. The results confirm on an empirical basis that the spin echo NMR technique can provide accurate dipole-dipole coupling information (and thus distance distributions) in disordered solids and glasses, h’er~~rl.~: phosphides: solid state NMR; dipolar coupling zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFE Introduction Solid state NMR has proven to be a powerful tool for addressing a wide variety of structural questions in disordered materials such as glasses and ceramics. Its usefulness stems from the pres- ence of internal interactions, which reflect the local chemical environment and which produce perturbations to the main Zeeman interaction. Among the various types of local interactions, the magnetic dipole-dipole coupling is of special sig- nificance, because it is the only one that is calcu- lable from first principles on the basis of struc- Correspomknce to: Dr. H. Eckert, Department of Chemistry, University of California, Santa Barbara, Goleta. CA 93106, USA. tural data. Experimental techniques that can ac- curately extract such dipole coupling information are therefore of key interest. Previous investigations have indicated that the measurement of Hahn spin echo intensity as a function of evolution time holds considerable promise in this regard. For example, spin echo NMR has been used to examine and derive de- tailed atomic distribution models for phosphorus atoms dispersed in amorphous hydrogenated sili- con [l-31, phosphorus and fluorine in silica glass [4,5], and phosphorus atoms in a number of cova- lent non-oxidic glasses [6-121. Various scattered applications to crystalline model compounds have produced good agreement between experimental and calculated dipolar couplings in some cases [7,13,141 and dramatic disagreement in certain other cases [7,15,161. 0976-704o/Y?/sl)S.O~ 80 1981 - Elsevier Science Publishers B.V. All rights reserved