H-1-AL-27 HETERONUCLEAR DIPOLAR COUPLINGS AND INTERNUCLEAR DISTANCES IN ALUMINA - SEDOR AND REDOR AL-27 STUDY

Double-resonance spin-echo NMR techniques (SEDOR and REDOR) are used to study heteronuclear connectivities in two aluminas, gibbsite and super5. In gibbsite (SEDOR), we describe a new procedure which allows one to estimate average internuclear distances when the 'isolated pair approximation' does not hold. In super5, a comparative examination of REDOR responses with one pulse and cross-polarization excitation results in obtaining structural information concerning the surroundings of four-, five- and six-coordinated Al sites and in discriminating between surface, intermediate and bulk species.