Ist ⁹¹Zr-Festkörper-Kernresonanzspektroskopie praktikabel?

Abstract

Herrn Prof. W . Müller-Warmuth zum 65. Geburtstag gewidmet Is solid state 91 Zr NMR feasible? 91Zr solid state NMR spectra have been observed for samples possessing different zirconium local-site environments (e.g. phosphates, fluorides). Depending on the quadrupole coupling, different NMR experiments have been utilized. In case of weak quadrupole coupling, magic angle spinning (MAS) is suitable. Otherwise, spin echo techniques are necessary to overcome "acoustic ringing" and receiver dead-time limitations. Using the step echo method, the detection of the very broad 91Zr signals is not limited by non-uniform spectral excitation. The obtained 91Zr chemical shifts range from -246 ppm to 208 ppm, the quadrupole coupling frequencies from 50 kHz to 2.7 MHz.

Solid-State 91Zr NMR of Bis(cyclopentadienyl)dichlorozirconium(IV)

“…The difference in isotropic shifts between powdered Cp 2 ZrCl 2 and the same sample dissolved in CH 2 Cl 2 (i.e., δ iso ) 0.0 ppm) can be attributed to solvent effects and/or crystal packing. The SIMPSON and MAS envelope simulations (Figure 4b,c) yield C Q ) 6.35 (10) MHz, which is comparable to some of the relatively smaller C Q ( 91 Zr) values measured previously by Hartmann and Scheler in various zirconates, 15 and η Q ) 0.3 (1). There are actually two distinct Cp 2 ZrCl 2 molecules in the unit cell with magnetically non-equivalent 91 Zr nuclei; 37 however, their structures are alike, and the values of C Q , η Q , and δ iso are expected to be very similar.…”

“…Due to both the broadening of solid-state NMR powder patterns by the second-order quadrupolar interaction and the generally poor receptivity of 91 Zr, many of these spectra require the acquisition of hundreds of thousands of transients to obtain a reasonable signal-to-noise (S/N) ratio. Further, if the 91 Zr quadrupolar interaction is large, the breadth of the 91 Zr spectrum exceeds excitation bandwidths at standard magnetic field strengths (i.e., 9.4−14.1 T); thus, in some cases it is necessary to collect spectra that are 50−600 kHz wide in a stepwise manner (in frequency offset increments), which is a very time-consuming process. , In addition, many of the spectra acquired by stepped-echo techniques lack the definition (i.e., S/N ratio and spectral resolution) required to obtain accurate chemical shielding and quadrupolar parameters from spectral analysis.…”

“…Further, if the 91 Zr quadrupolar interaction is large, the breadth of the 91 Zr spectrum exceeds excitation bandwidths at standard magnetic field strengths (i.e., 9.4-14.1 T); thus, in some cases it is necessary to collect spectra that are 50-600 kHz wide in a stepwise manner (in frequency offset increments), which is a very time-consuming process. 14,15 In addition, many of the spectra acquired by stepped-echo techniques lack the definition (i.e., S/N ratio and spectral resolution) required to obtain accurate chemical shielding and quadrupolar parameters from spectral analysis.…”

Multinuclear NMR study of silica fiberglass modified with zirconia

“…Only a few 91 Zr NMR studies in materials have so far been reported in the literature [24,[28][29][30][87][88][89][90][91][92][93][94][95]. Most recent research fully utilizes advantages of performing 91 Zr NMR experiments at ultrahigh magnetic fields, some examples include microporous and layered zirconium phosphates [28,96] and metallocene catalysts [97].…”

Solid-State 91Zr NMR Spectroscopy Studies of Zirconocene Olefin Polymerization Catalyst Precursors

“…Previous studies have been limited to extended systems such as zirconium oxides, phosphates, silicates, and halides. [59][60][61][62][63][64][65][66][67][68][69][70][71][72] Our previous work on Cp 2 ZrCl 2 remains the only example of a molecular system studied by 91 Zr SSNMR. 54 Therefore, it is of importance to initially characterize model zirconocene compounds in order to correlate the structural features of metallocenes with the NMR interaction tensor parameters obtained from experimental NMR spectra.…”