Measurement of quadrupolar coupling constants, shielding tensor elements and the relative orientation of quadrupolar and shielding tensor principal axis systems for rubidium-87 and rubidium-85 nuclei in rubidium salts by solid-state NMR

Abstract

The spin lattice relaxation time, T , , quadrupolar coupling constant, and chemical shielding tensor elements of several for IH's. Typical relaxation times for 87Rb are in the range of 100-300 ms and 50-300 ms for 85Rb. The Q , values are in the range of 7-14 MHz for 85Rb and 3-1 1 MHz for 87Rb. A program was created to numerically simulate and fit experimental powder patterns for the &/2 central transition, where the principal axis systems (PAS) of the shielding and quadrupole tensors are not coincident. The analysis shows that having both nuclides available with significantly different quadrupole coupling constants makes the general line-shape problem more tractable. That is, the 85Rb data provides an excellent visualization of chemically different rubidium atoms when there are significant differences in the value of Q , . Such data would be difficult to extract from the corresponding 87Rb line shapes due to the smaller value of Q , . The 87Rb nuclide, however, because of its smaller value of Qa, provides an excellent opportunity to observe the consequences of the noncoincident PAS frames between the shielding and quadrupole tensors.rubidium salts have been surveyed at the frequency 130.88 MHz for 9, ' 7Rb and 38.64 MHz for 85Rb, i.e. 9.4T, or 400 MHz IntroductionRubidium has two stable isotopes, 85Rb (I = 5 / 2 ) and 87Rb (I = 3/2), which are amenable to the NMR experiment. The natural abundances of these nuclides are 72.8% and 27.2% for 85Rb and 87Rb, respectively. Typically, only the *1/2 central transition is observed in solid-state rubidium NMR. The other transitions are very broad, and the quadrupole coupling constant is sufficiently large to prevent excitation of these transitions. The moderate

Quadrupole Coupling and Anisotropic Shielding from Single-Crystal NMR of the Central Transition for Quadrupolar Nuclei.87Rb NMR of RbClO4and Rb2SO4

“…We here report small or intermediate quadrupole couplings (5,6) or (ii) the single-crystal 87 Rb NMR studies for RbClO 4 and Rb 2 SO 4 , highly distorted lineshape for the central transition when in particular for comparison of the parameters for the two larger quadrupolar couplings are operative (7,8). However, tensorial interactions with the corresponding values deterfor most quadrupolar nuclei, the CSA is a quite small interacmined recently from static and MAS NMR (2,3,7,8), tion and, unfortunately, the effect of the CSA on the spectral which showed some discrepancies. Combining the results of appearance can easily be eliminated or drastically reduced by MAS even at fairly low spinning speeds.…”

“…The present work demonstrates that, for half-integer quadpowders have shown that the magnitudes of the two tensorial rupolar nuclei, the quadrupole-coupling and CSA tensors interactions as well as their relative orientation may be obmay conveniently be determined from single-crystal NMR tained from the lineshape of the central transition (1)(2)(3) or of the central transition for very small CSAs. 87 Rb (I Å 3 2 ) from a spectrum of all transitions (4).…”

“…More importantly, it quadrupole-coupling constants as large as C Q Å 11. 5 MHz has recently been demonstrated that these parameters can be and 87 Rb CSAs between approximately Éd s É Å 10 and 145 determined with high accuracy and with improved spectral ppm have been reported for rubidium salts (2,3,7,8, sensitivity and resolution employing magic-angle spinning 13, 14). Thus, the determination of the two interactions from (MAS) of polycrystalline powders (5).…”

An Investigation of Lanthanum Coordination Compounds by Using Solid‐State 139La NMR Spectroscopy and Relativistic Density Functional Theory

“…d 33 , and the relative orientation of EFG and chemical-shift tensors may also influence the 139 La NMR lineshape. [45,46] The EFG tensor is described by the nuclear quadrupolar coupling constant, C Q = eQV ZZ h À1 , where e is the elementary charge, Q is the nuclear quadrupole moment, and h is the Planck constant, and the asymmetry parameter, ), which is restricted to values between À1 and + 1. [47] The relative orientation of the EFG and chemical-shift tensors is defined by the Euler angles-a, b, and g-and thus a total of eight parameters describe the NMR spectra, theoretical examples of which are presented in Figure 1 Typical experimental 139 La NMR spectra of solid lanthanum(iii) coordination compounds at applied magnetic fields of 11.75 and 17.60 T can be found in Figures 2-5.…”

The Zintl Phase Cs7NaSi8 – From NMR Signal Line Shape Analysis and Quantum Mechanical Calculations to Chemical Bonding

“…Sites of general symmetry do not obey these constraints resulting in more complex line shapes. [39] The relative orientation of both PAS is described by Euler angles α, β, and γ. We refer to the right handed rotation as R(αβγ) = R z (γ) R y (β) R z (α).…”