Solid State Nuclear Magnetic Resonance 30 (2006) 55–59 Hardware modification of a 7 mm MAS NMR probe to a single-crystal goniometer Ga´bor Kova´cs, Ja´nos Rohonczy à Department of General and Inorganic Chemistry, Institute of Chemistry, Eo¨tvo¨s Lora´nd University, Budapest, Hungary Received 26 October 2005; received in revised form 31 January 2006 Abstract Tensorial terms of the Hamiltonian can be measured by solid-state single-crystal nuclear magnetic resonance (NMR) spectroscopy which requires a goniometer NMR probehead. Goniometer probes; however, are not standard parts of solid NMR spectrometers and are available only at a much higher price than magic-angle spinning (MAS) probeheads widely used in research. Due to requirements of MAS experiments, modern probeheads are designed for small ceramic rotors, which are 1–4 mm in diameter, to reach very high angular frequencies, so there are several older 7 mm MAS probeheads used rarely todays in NMR laboratories. In this paper, a simple method is presented how to rebuild step-by-step a 7 mm Bruker MAS probehead to be suitable for single-crystal spectroscopy. In the second part 31 P chemical shift tensors of Na 4 P 2 O 7  10H 2 O are determined to demonstrate the functionality of the rebuilt probehead. r 2006 Elsevier Inc. All rights reserved. Keywords: NMR; Single crystal; MAS probe; ASICS; Goniometer; Sodium pyrophosphate; Home-built probehead; Nuclear magnetic resonance; 31-P NMR; Crystal orientation 1. Introduction Several magnetic interactions are known in the nuclear magnetic resonance (NMR) spectroscopy, thus many tensorial terms appear in the Hamiltonian. Most important ones are chemical shielding, dipolar and quadrupolar coupling. In solid state, the intermolecular distances and orientations are fixed and NMR spectra become sensitive of crystal orientation. In single crystals, macroscopic orientation correlates directly with molecular orientation. This makes it possible to determine not only the isotropic average but all components of tensors. Knowing these values may give further details on microscopic structure, bonds in solid state, etc. Theoretical calculations also provide primarily tensorial components and they are averaged mathematically later in NMR spectra simula- tions. In testing the accuracy of mathematical methods comparing of tensorial elements directly is a better way than comparing simulated isotropic spectra. As these NMR experiments require large single crystals that in many cases hardly available, other methods have been developed to determine anisotropy components. Principal values of chemical shielding and partial informa- tion on orientation can be obtained analyzing rotational sidebands in magic-angle spinning (MAS) experiments or using two-dimensional methods [1–4]. All techniques using powder samples; however, can supply only relative information on tensor orientations, i.e. orientation between shielding tensors of different nuclei. To determine orienta- tion relative to the crystal lattice the most straightforward way is still to use solid-state single-crystal spectroscopy. In such an experiment, several NMR spectra need to be recorded of one single crystal, knowing the direction of the crystal axes in the laboratory frame for each spectrum. The experiment requires a goniometer NMR probehead for exact orientation of the crystal. Goniometer probes; however, are not standard parts of solid NMR spectro- meters and are available only at a much higher price than MAS probeheads widely used in research today or they must be constructed at home [5–7]. In this technical paper, a simple method to rebuild a 7 mm Bruker MAS probehead to be suitable for single-crystal spectroscopy is presented. ARTICLE IN PRESS www.elsevier.com/locate/ssnmr 0926-2040/$ - see front matter r 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.ssnmr.2006.02.002 à Corresponding author. Fax: +36 1 372 2909. E-mail address: rohonczy@para.chem.elte.hu (J. Rohonczy).