Satellite-Transition MAS NMR of Spin I = 3/2, 5/2, 7/2 and 9/2 Nuclei: Sensitivity, Resolution and Practical Implementation

The satellite-transition MAS (STMAS) experiment offers an alternative approach to established methods such as dynamic angle spinning (DAS), double rotation (DOR), and multiple-quantum MAS (MQMAS) for obtaining high-resolution NMR spectra of half-integer quadrupolar nuclei. Unlike the multiple-quantum experiment, STMAS involves two-dimensional correlation of purely single-quantum coherences; satellite transitions in t(1) (or F-1) and the central transition in t(2) (or F-2). To date, STMAS has primarily been demonstrated for nuclei with spin quantum numbers I = 3/2 and, to a lesser extent, I > 5/2. However, many chemically relevant nuclei possess I > 3/2, such as O-17 and Al-27 (both I = 5/2), Co-59 (I = 7/2), and Nb-93 (I = 9/2). Here, we discuss the application of STMAS to nuclei with spin quantum numbers from I = 3/2 to 9/2. First, we consider the practical implementation of the STMAS experiment using Rb-87(I = 3/2)NMR as an example. We then extend the discussion to include nuclei with higher spin quantum numbers, demonstrating Al-27, Sc-45 (I = 7 /2), Co-59, and Nb-93 STMAS experiments on both crystalline and amorphous samples. We also consider the possibility of experiments involving satellite transitions other than m(I) = 1/2 <-> +/- 3/2 and, using Nb-93 NMR, demonstrate the correlation of all single-quantum satellite transitions up to and including m(I) = +/-7/2 <->+/- 9/2. The absolute chemical shift scaling factors in these experiments are discussed, as are the implications for isotropic resolution. (C) 2002 Elsevier Science (USA).