Obtaining accurate chemical shifts for all magnetic nuclei (¹H, ¹³C, ¹⁷O, and ²⁷Al) in tris(2,4-pentanedionato-O,O′)aluminium(III) — A solid-state NMR case study

Abstract

We report a complete set of high-resolution solid-state NMR spectra for all magnetic nuclei (1H, 13C, 17O, and 27Al) in the α-form of tris(2,4-pentanedionato-O,O′)aluminium(III), α-Al(acac)3. These high-resolution NMR spectra were obtained by using a host of solid-state NMR techniques: standard cross-polarization under the magic-angle spinning (CPMAS) method for 13C, 1-D homonuclear decoupling using the windowed DUMBO sequence for 1H, double-rotation (DOR) for 17O and 27Al, and multiple-quantum MAS for 27Al. Some experiments were performed at multiple magnetic fields. We show that the isotropic chemical shifts obtained for 1H, 13C, 17O, and 27Al nuclei in α-Al(acac)3 are highly resolved and accurate, regardless of the nature of the targeted nuclear spins (i.e., spin-1/2 or quadrupolar) and, as such, can be treated equally in comparison with computational chemical shifts obtained from a gauge-including projector-augmented wave (GIPAW) plane-wave pseudopotential DFT method.

Solid‐State 17O NMR Spectroscopy of Paramagnetic Coordination Compounds

“…As seen in Figure 1, the static solid‐state 17 O NMR spectrum for [V([ 17 O 2 ]acac) 3 ] exhibits signals centered at around −1300 ppm and spanning over 1800 ppm. These spectral features are drastically different from those obtained for the diamagnetic analogue [Al([ 17 O 2 ]acac) 3 ], which has the 17 O NMR signal at 270 ppm with a spectral span of only 400 ppm at 21.1 T 20. For [V([ 17 O 2 ]acac) 3 ], we were able to obtain a very fast MAS 17 O NMR spectrum in which all six crystallographically non‐equivalent oxygen sites21 are resolved.…”

“…In comparison, the isotropic 17 O chemical shifts for the six oxygen atoms in the diamagnetic Al([ 17 O 2 ]acac) 3 differ by only 5 ppm. [20] K 3 V([ 17 O 4 ]oxalate) 3 ·3H 2 O is an interesting compound in which both direct chelating (O1, O2, O3) and non-bonding (O4, O5, O6) oxygen atoms are present. [22] As seen from Figure 1, the 17 O NMR signals from O1-O3 are found around −1200 ppm whereas those from O4-O6 appear at 350 ppm.…”

“…The 17 O isotropic shifts among the six directly bonded oxygen atoms differ by more than 500 ppm. In comparison, the isotropic 17 O chemical shifts for the six oxygen atoms in the diamagnetic [Al([ 17 O 2 ]acac) 3 ] differ by only 5 ppm 20. K 3 [V([ 17 O 4 ]oxalate) 3 ]⋅3 H 2 O is an interesting compound in which both direct chelating (O1, O2, O3) and non‐bonding (O4, O5, O6) oxygen atoms are present 22.…”

Ultra-high resolution 17O solid-state NMR spectroscopy of biomolecules: A comprehensive spectral analysis of monosodium L-glutamate·monohydrate

“…In particular, recent demonstrations on 17 O DOR spectroscopy have reported ultra-high spectral resolution with linewidths of <1 ppm). [15][16][17][18][19][20][21] It is worth noting that high-resolution 17 O NMR MQMAS and DOR have also been reported for many important inorganic materials. 5,[22][23][24] In comparison to inorganic materials, there are three major complications for 17 O solid-state NMR on bio/organic molecules: (1) the abundance of hydrogen in bio/organic molecules gives rise to significant dipolar broadening unless high power 1 H-decoupling is applied; (2) the quadrupole interaction is generally larger (7- 33 was used.…”

Solid-state 17O NMR study of α-d-glucose: exploring new frontiers in isotopic labeling, sensitivity enhancement, and NMR crystallography

“…Ideally, one should utilize all available magnetically-active nuclei in a molecular system as a general approach of "NMR crystallography". 74 Now, what are the reasons for the 17 O-H•••Cldimers are 3.6 and 13.5 kcal mol -1 , respectively. 75 While hydrogen-bonding effects on 17 O NMR parameters are well known for carbonyl compounds, [76][77][78][79][80][81][82][83][84][85][86] data on hydroxyl and ether functional groups are scarce in the literature.…”