Estimating internuclear distances between half-integer quadrupolar nuclei by central-transition double-quantum sideband NMR spectroscopy

We demonstrate the estimation of homonuclear dipolar couplings, and thereby internuclear distances, between half-integer spin quadrupolar nuclei by central-transition (CT) double-quantum (2Q) sideband nuclear magnetic resonance (NMR) spectroscopy. It is shown that the rotor-encoded sideband amplitudes from CT 2Q coherences in the indirect dimension of the two-dimensional NMR spectrum are sensitive probes of the magnitude of the homonuclear dipolar coupling, but are significantly less affected by other NMR parameters such as the magnitudes and orientations of the electric field gradient tensors. Experimental results of employing the R221R22?1 recoupling sequence to the 11B spin pair of bis(catecholato)diboron resulted in an estimation of the internuclear B-B distance as (169.6±3)pm, i.e., with a relative uncertainty of±2%, and in excellent agreement with the distance of 167.8pm determined by single-crystal X-ray diffraction. © 2011 Published by NRC Research Press.