O MAS NMR Reveals - ACS Publications - American Chemical Society

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High-Field 17O MAS NMR Reveals 1J(17O-127I) with its Sign and the NMR Crystallography of the Scheelite Structures for NaIO4 and KIO4 Hans J. Jakobsen,*,† Henrik Bildsøe,† Michael Brorson,‡ Gang Wu,*,§ Peter L. Gor’kov,∥ Zhehong Gan,∥ and Ivan Hung∥ †

Danish Instrument Centre for Solid-State NMR Spectroscopy, Interdisciplinary Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark ‡ Haldor Topsøe A/S, Nymøllevej 55, DK-2800 Lyngby, Denmark § Department of Chemistry, Queen’s University, Kingston, Ontario, Canada K7L 3N6 ∥ National High Magnetic Field Laboratory, 1860 East Paul Dirac Drive, Tallahassee, Florida 32310, United States ABSTRACT: High-field, ambient-temperature (AT) 17O MAS NMR spectra of the tetraoxoanion IO4− in NaIO4 and KIO4 exhibit unusual line-shape features for the central transition (CT), which so far have not been observed in any second-order broadened line shape for the CT of a quadrupolar nucleus. These features are caused by an unusually large isotropic 1J(17O-127I) spin coupling (∼500 Hz) and appear like “teeth-on-a-saw”. This study reports interesting results obtained from optimized fitting of the spectra using our recently described XSTARS software. The results include determination of a positive sign for 1 17 J( O-127I) (= +500 Hz), an unusual observation in solid-state NMR. NMR crystallography shows a very precise correlation between extraordinary small changes for the 17O asymmetry parameter (ηQ) and changes for a tetrahedral O−I−O angle upon distortion from an ideal tetrahedron. Similarly, the spectral analysis shows that the NMR crystallography requires the principal axes Vzz(17O) and δzz(17O) of the PAS for these tensors are both almost along the I−O bond. All the experimental data are in excellent agreement with our ADF and CASTEP calculations.

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relaxation and/or self-decoupling. High-magnetic fields and high-resolution techniques, such as MQMAS, DAS, and DOR, have been used to reduce or remove the quadrupolar broadening, and variable temperatures are often needed to change the molecular dynamics and its line broadening effect in order to reveal the relatively small scalar J couplings.2−4 A list of references to recent determinations of such 1J(X-Y) indirect coupling constants, using the specialized solid-state NMR pulse-sequences of MQMAS, DAS, and DOR, can be found in ref 4. During these investigations, we have been asked by several inorganic chemists to perform related 17O MAS NMR studies for other tetraoxoanion salts. A series of tetraoxoanions for the perhalides [i.e., perchlorates (ClO4−), perbromates (BrO4−), and periodates (IO4−)], immediately came to mind. However, it is known that the ClO4− ion does not exchange its oxygen atoms to a measurable extent with water over long periods of time at elevated temperatures and high acidities.5,6 This fact was actually fully confirmed in the early stages of our 17O MAS NMR studies by unsuccessful attempts to 17O-enrich the ClO4− ion in KClO4, according to our standard procedure using 10%

INTRODUCTION NMR crystallography, as related to high-resolution solid-state NMR of powder samples, has evolved into an extremely important box of tools for structural and dynamic studies within chemistry, materials, and biochemistry during the past few decades.1 In this respect, 17O appears to be a quite useful quadrupolar nucleus because of the straightforward measurements of its isotropic/anisotropic chemical shifts, quadrupolar coupling parameters, and in some cases even J(17O-Y) spin couplings, but primarily due to the widespread occurrence of oxygen in nature. 17O is a spin I = 5/2 nucleus, however, of very low natural abundance, but many compounds can fairly easily be 17O-enriched to an appropriate level for solid-state NMR measurements. In a recent series of solid-state variabletemperature (VT) 17O MAS NMR investigations of some tetraoxometal anions2−4 (WO42−,2,3 ReO4−,4 and MnO4−,3) salts with different monovalent cations (e.g., K+,2−4 Cs+,2,3 and NH4+,4), we determined the first detailed dynamics, thermodynamics, and 17O spectral parameters in such systems.2−4 Highresolution 17O MAS NMR obtained at low-temperatures has allowed direct observation of one-bond indirect 1J(17O-187Re) spin couplings in two perrhenates.4 This observation is among the only few measurements of indirect spin couplings between two quadrupolar nuclei that are often obscured by large quadrupolar broadening and dynamic broadening effects like © 2015 American Chemical Society

Received: April 18, 2015 Revised: June 1, 2015 Published: June 2, 2015 14434

DOI: 10.1021/acs.jpcc.5b03721 J. Phys. Chem. C 2015, 119, 14434−14442

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The Journal of Physical Chemistry C

(23 °C) (i.e., at an actual sample temperature of ∼50 °C), based on the temperature calibration performed at the NHMFL for the 3.2 mm Revolution NMR MAS systems using Pb(NO3)2.14 Most importantly, a high-temperature 17O MAS NMR experiment performed at 80 °C for the NaIO4 and KIO4 samples, with the aim to observe any effects on the line shape and resolution, showed no change at all compared to the AT experiment. All 17O MAS NMR spectra acquired on this spectrometer used standard single-pulse excitation at 112.8 MHz, which focused on the central part of the spectrum [i.e., the 17O Central Transition (CT)]. 17O chemical shifts were referenced to the 17O resonance of an external sample of ordinary H2O. A 90° flip-angle pw(90)liquid = 5.0 μs was obtained for the 17O resonance of ordinary H2O while a value of pw = 1.2 μs, which corresponds to a liquid 22° flip-angle (or a solids 65° flip angle) for the rf field strength of 50 kHz, was used for the MAS experiments. This one-pulse excitation was used for the solid-state MAS experiments along with a relaxation delay of 10 s for both samples. The employed spinning frequencies (νr) for the final spectra are shown in the figure captions with an estimated stability Δνr < ± 2 Hz for both samples. The magic angle θ = 54.736° was adjusted to the highest possible precision (Δθ < ± 0.003°) by 23Na MAS NMR using a sample of NaNO3 at 219.7 MHz, as described elsewhere.15 Bruker 900 MHz Avance II 21.1 T Spectrometer. In order to further separate the spinning sidebands, 17O MAS NMR spectra were also recorded at the slightly higher 21.1 T field of the Bruker 900 MHz Avance II spectrometer at the National Ultrahigh-Field NMR Facility for Solids with a high spinning frequency νr ∼ 31 kHz, using 2.5 mm o.d. Bruker MAS rotors. This was done to confirm the spectral parameters determined at 19.6 T from spectral simulations (in particular the 17O chemical shift anisotropy (CSA) parameters due to the decreased intensity of the first order ssbs caused by the higher νr). The 17O MAS NMR experiments acquired on this spectrometer, equipped with a standard narrow-bore (52 mm i.d.) magnet, were obtained at 122.0 MHz using a Bruker broadband X-{1H} double-resonance MAS probe. The AT 31 kHz MAS for the 2.5 mm rotor induced a sample heating of ∼40 °C, according to the temperature calibration for the 2.5 mm MAS probe, so the actual sample temperature is ∼63 °C. Again 17O chemical shifts were referenced to the 17O resonance of an external sample of ordinary H2O. A 90° flip-angle pw(90)liquid = 2.0 μs was obtained for the 17O resonance of ordinary H2O while a value of pw = 0.67 μs, corresponding to a liquid 30° flip-angle (or a solids 90° flip angle) for the rf field strength of 125 kHz, was used for the first pulse in a standard solid-state spin−echo 90°−180° MAS experiments used on this spectrometer. The few experiments acquired on this spectrometer were performed mainly to confirm the magnitude of the 17O quadrupole coupling and CSA parameters determined at 19.6 T. The determination of the 17O CSA parameters at 19.6 T are based on the relative intensities between the centerband for the central transition (CT) and its associated first- and second-order spinning sidebands (ssbs) as observed from optimized fits of the experimental spectra. For this reason, the 17O MAS NMR spectra acquired at 21.1 T used a much higher spinning frequency νr ∼ 31 kHz in order to confirm the expected increase in the relative intensity ratios between the CT centerband and its first few ssbs. Spectral Analysis. All 17O AT MAS NMR spectra have been analyzed in terms of the 17O and 127I spectral parameters

O-enriched H2O at 100 °C for other tetraoxoanions,2−4 since no 17O resonance was observed from 17O MAS NMR experiments of the isolated KClO4 samples. On the other hand, it is known, at least qualitatively, that the reactivity of oxygen exchange with water increases in the series ClO3− < BrO3− < IO3−.5 Thus, this study reports some exciting 17O MAS NMR results for two periodates following successful 17Oenrichments of NaIO4 and KIO4 by our standard procedure used recently.2−4 These results include: (i) the first direct observation at ambient-temperature (AT) of a 1J(17O-Me) indirect spin coupling between two quadrupolar nuclei in solid tetraoxoanions (where Me is either a metal or metalloid/ nonmetal), (ii) the determination of an unusually large magnitude for 1J(17O-127I), but most importantly its opposite sign compared to our most recent results for 1J(17O-Me) spin couplings between 17O and a true metal (Me),4 and (iii) first of all the NMR crystallography revealed for the IO4− anion resulting from in-depth simulations of the acquired experimental 17O AT MAS NMR spectra. All experimental 17O spectral parameters are determined from optimized fits to these spectra using our recently developed XSTARS software, which includes all solid-state NMR interactions (including the direct dipolar D(X-Y) and indirect J(X-Y) spin coupling), and finally the relative tensor orientations for the two (X and Y) quadrupolar nuclei.4 XSTARS is an extended version of the most recently updated standard version of STARS.3 The determined J-coupling constant including its sign, chemical shift, and quadrupolar coupling parameters are all in excellent agreement with ADF (Amsterdam density functional)7−10 and CASTEP11 calculations that we performed for the corresponding parameters based on refined single-crystal XRD structures for NaIO412 and KIO4.13 17

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EXPERIMENTAL SECTION Materials and Synthesis. Standard samples of NaIO4 and KIO4 are commercially available. They were purchased from Aldrich and used without further purification. 17O-enrichments of the samples were achieved by 17O-exchange in sealed glass ampules, each containing a 10% 17O-enriched H2O solution of the sample and kept at a temperature of 90−100 °C for 7 days according to the procedure used for 17O-enrichment of our other tetraoxoanion salts.3,4 The 10% 17O-enriched H2O used for the 17O-exchange was purchased from CortecNet, France. Solid-State MAS NMR Spectroscopy. 17O MAS NMR experiments were performed at the National High Magnetic Field Lab (NHMFL), Florida State University (FSU), Tallahassee, and at the National Ultrahigh-Field NMR Facility for Solids, Ottawa, Ontario, Canada, on two different high-field spectrometers. Bruker DRX-830 Narrow-Bore 19.6 T Spectrometer. 17O MAS NMR spectra intended to retrieve the 17O spectral parameters from precise spectral simulations were acquired using the Bruker DRX-830 narrow-bore 19.6 T spectrometer at the NHMFL. This spectrometer is equipped with a special Magnex narrow-bore (31 mm i.d.) magnet and a NHMFL designed and home-built extremely narrow-bore (31 mm o.d.) double-resonance X-{1H} broadband MAS probe for 3.2 mm o.d. rotors (i.e., the magnet shim coil was removed). The samples were spun at νr ∼ 18 kHz using a 3.2 mm o.d. MAS rotor/stator module from Revolution NMR. All experiments were performed using ambient-temperature (AT) nitrogen gas for the air-bearing and drive gas. The effect of heating the sample by MAS at 18 kHz is estimated to be ∼25 °C above AT 14435

DOI: 10.1021/acs.jpcc.5b03721 J. Phys. Chem. C 2015, 119, 14434−14442

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RESULTS AND DISCUSSION NaIO4, 10% 17O-Enriched Sample. The experimental single-pulse 19.6 T (112.8 MHz) 17O MAS NMR spectrum for the ∼10% 17O-enriched sample of NaIO4 is displayed in Figure 1a for the central spectral region (for a spectral width of 150

and for parameters which describe the combined interactions between the 17O and 127I quadrupolar nuclei [e.g., the direct dipolar 1D(17O-127I) and indirect scalar 1J(17O-127I) couplings] using our recently developed XSTARS software presented in detail elsewhere.4 This new XSTARS software is an extension of our standard16 and updated3 STARS simulation/iterative fitting software. The XSTARS software has, similar to the updated STARS version,3 been incorporated into the Varian VnmrJ software running on a Linux RedHat PC. All spectra were processed using a 28656 crystallite file generated with the Zaremba-Conroy-Wolfsberg (ZCW) algorithm.17−19 For the quadrupole coupling and chemical shift parameters, we employ the original conventions16 which still apply for STARS and XSTARS, in other words CQ = eQVzz /h

ηQ = (Vyy − Vxx )/Vzz

(1)

δσ = δiso − δzz

ησ = (δxx − δyy )/δσ

(2)

δiso = (1/3)(δxx + δyy + δzz) = (1/3)Tr(δ)

(3)

δJ = Jzz − Jiso

(4)

ηJ = (Jyy − Jxx )/δJ

Jiso = (1/3)(Jxx + Jyy + Jzz ) = (1/3)Tr(J )

Article

(5)

with the convention |λzz − (1/3)Tr(λ)| ≥ |λ xx − (1/3)Tr(λ)| ≥ |λ yy − (1/3)Tr(λ)|

Figure 1. 112.8 MHz (19.6 T) experimental and simulated 17O MAS NMR spectra of NaIO4 obtained for a spinning frequency νr = 18.55 kHz at AT and presented on a ppm scale corresponding to a total width of the spectra on a frequency scale of 150 kHz. The experimental spectrum was acquired using 18063 scans for about 2 days and 2 h for a relaxation delay of 10 s employing the flip angle conditions described in the Experimental Section for this spectrometer as noted in the section on “Spectral Analysis”. We point out that all experimental and simulated spectra in Figures 1−5 were processed using a 28656 crystallite file generated with the Zaremba-ConroyWolfsberg (ZCW) algorithm.17−19 (a) Expansion for the centerband region of the experimental spectrum according to the two scales mentioned above. (b) Optimized simulation, including the 17O CT and all STs, of the experimental spectrum in (a) and shown on the same frequency scales as in (a). (c) Corresponding simulation for the CT only. (d) Corresponding simulation of the two outer STs for the 17 O spin I = 5/2 nucleus. Addition of the simulations in (c) and (d) corresponds to the simulated spectrum in (b). All simulated spectra used the optimized parameters listed in row 1 of Table 1.

(6)

for the principal elements (λαα = Vαα, δαα) of the quadrupole and chemical shift tensors. The orientation of a tensor relative to a molecular coordinate system is described by the three Euler angles (ψ, χ, ξ) which correspond to positive rotations of the tensor principal axis system around z(ψ), the new y(χ), and the final z(ξ) axis. ADF and CASTEP Calculations. Computations of NMR tensors were performed using the Amsterdam density functional (ADF) software package.7−10 The Vosko-Wilk-Nausir (VWN) exchange-correlation functional20 was used for the local density approximation (LDA), and the Perdew−Burke− Ernzerhof (PBE) exchange-correlation functional21 was used for the generalized gradient approximation (GGA). Standard Slater type-orbital (STO) basis sets with triple-ζ quality plus polarization functions (TZ2P) were used for all of the atoms. The spin orbital relativistic effect was incorporated in all calculations via the zero order regular approximation (ZORA).22−25 Plane-wave pseudopotential DFT calculations of the NMR tensors were performed using Materials Studio CASTEP software version 4.4 (Accelrys).11 The Perdew− Burke−Ernzerhof (PBE) functionals21 were employed in all calculations in the generalized gradient approximation (GGA) for the exchange correlation energy. On-the-fly pseudo potentials were used with a plane wave basis set cutoff energy of 550 eV. The Monkhorst−Pack26 k-space grid sizes were 5 × 5 × 2 (7 k-points used) and 4 × 4 × 2 (4 k-points used) for NaIO4 and KIO4, respectively. The reported crystal structures of NaIO4 (ICSD 14287)12 and KIO4 (ICSD 83376)13 were used as already mentioned in the Experimental Section. In the above calculations, computed 17O magnetic shielding values (σ in ppm) were converted to chemical shifts (δ in ppm) by using δ = 287.5 ppm − σ.27

kHz) and using a spinning frequency νr = 18.55 kHz. In addition to the intense centerband for the CT, quite intense first- and second-order ssbs are observed for the CT, due to a large 17O CSA, along with several ssbs arising from the 17O satellite transitions (STs). Optimized XSTARS fitting is performed for both the CT and STs and the resulting final fitted/simulated spectrum is shown in Figure 1b, while the corresponding optimized 17O/127I spectral parameters are summarized in Table 1. We note that for the simulation of this 19.6 T (112.8 MHz) 17O MAS NMR spectrum, we used an 127 I NMR resonance frequency ν(127I) = 166.4 MHz and the 127 I quadrupole coupling parameters CQ = 42.2 MHz and ηQ = 0.0 reported earlier for NaIO4.28 In order to identify the origin of the individual ssbs in the experimental/simulated 17O MAS NMR spectra in Figure 1 (panels a and b), simulated 17O MAS 14436

DOI: 10.1021/acs.jpcc.5b03721 J. Phys. Chem. C 2015, 119, 14434−14442

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Table 1. 17O Quadrupole Coupling (CQ, ηQ), Chemical Shift Parameters (δσ, ησ, δiso), Effective Dipolar Coupling D′(17O-127I) = D − δJ/2, Isotropic Coupling J = 1J(17O-127I), and Its Anisotropy δJ, Determined from 17O MAS NMR Spectra of NaIO4 and KIO4 at ATa sample experiment NaIO4/19.6 T NaIO4/21.1 T KIO4/19.6 T KIO4/21.1 T

temp (°C)

CQ (MHz)

ηQb

δσ (ppm)

ησ

δiso (ppm)

Jc (Hz)

D′ (Hz)

δJ (Hz)

∼ ∼ ∼ ∼

11.19 11.17 10.87 10.89

0.066 0.062 0.032 0.030

155 140 148 147

0.20 0d 0.20 0d

250 251 243 243

500 502 506 504

−532 −528 −417 −442

−110 −118 −366 −316

AT, AT, AT, AT,

50 63 50 63

a The δiso values (relative to H217O) have an error limit of ±0.5 ppm. The error limits for CQ and ηQ are ±0.02 MHz and ±0.005b, respectively. The error limits for δσ and ησ are ±10 ppm and ±0.05, respectively, for the 19.6 T data and about ±15 ppm for δσ determined at 21.1 T. The error limits for J = 1J(17O-127I) determined at both 19.6 and 21.1 T are only ±5 Hz. However, the error limits for D′ and δJ are generally much larger (∼ ±100 Hz) and could be even larger for the analyzed 21.1 T spectra. The Euler angles describing the tensor orientation for the 17O quadrupole and CSA principal axis systems (PAS) relative to our definition of the molecular frame system are discussed in the text. It is observed that for the two sensitive angles to the fitting process, β(Q) and β(δσ), it is only the difference β(Q) − β(δσ) which influences the optimized fitting. Thus, β(Q) = 0 is fixed and β(δσ) is the only Euler angle being allowed to vary, resulting in difference values β(Q) − β(δσ) = −12° ± 3° in all optimizations of the 19.6 T spectra. bSee text and Figure 6, which prove the extraordinary low error limit (±0.005) for these ηQ values. cSee text for the reasons why a positive sign is deduced for J = 1J(17O-127I). dThe two ησ = 0 values in Table 1 for the two spectra acquired at 21.1 T (122.0 MHz) are fixed during the optimization processes because of the much higher spinning frequency (νr ∼ 31 kHz) employed. This makes the small value ησ = 0.20 determined for νr ∼ 18 kHz at 19.6 T a very uncertain parameter to determine for νr ∼ 31 kHz at 21.1 T.

coupling (127I being a spin I = 5/2 nucleus). As illustrated by the two spectra in Figure 2 (panels a and b), the expected “sixpeak” splitting patterns on the flanks for both of the two “horns”, due to the indirect scalar 1J(17O-127I) coupling, appear as “seven-peak” patterns including the shoulders observed in the outer-region of the patterns for the two “horns” in the experimental as well as in the simulated spectrum. Optimized simulated spectra unambiguously show that the additional splitting into the apparent “seven-peak” pattern is caused by an extremely small value for the 17O asymmetry parameter (i.e., ηQ = 0.066). The fitting of the “seven-peak” pattern allows for a very precise determination of the asymmetry parameter. For example, changing ηQ = 0.066 to ηQ = 0.00 in a simulation, keeping all other NaIO4 parameters unchanged in Table 1, turns the “seven-peak” pattern into the originally expected “sixpeak” splitting pattern (not shown). This observation is in complete agreement with both ADF7−10 and CASTEP11 calculations of the spectral parameters based on refined single-crystal XRD structures for both NaIO412 and KIO413 (vide infra). To obtain additional confirmation on the 17O quadrupole coupling parameters and partly support the magnitude of the 17 O CSA parameters determined at 19.6 T (112.8 MHz), a 21.1 T (122.0 MHz) 17O MAS NMR experiment was performed at the much higher spinning frequency νr ∼ 31 kHz using a 2.5 mm rotor and a standard spin−echo 90°−180° MAS experiment. The experimental spin−echo 21.1 T 17O MAS NMR spectrum of NaIO4 for νr = 31.25 kHz is displayed in Figure 3a with an identical horizontal expansion in Hz (i.e., 150 kHz) as used for Figure 1. It clearly illustrates that the intensity decreases considerably of the first- and second-order ssbs for the CT due to the extensive increase in spinning speed, followed by a corresponding increase in mainly the left, highfrequency “horn” of the CT centerband. A simulated spectrum resulting from an optimized fit to the experimental spin−echo spectrum in Figure 3a using the XSTARS software is shown in Figure 3b. The resulting 17O spectral parameters are summarized in Table 1 along with the parameters determined from the 17O experimental 19.6 T spectrum in Figure 1a and its expansion in Figure 2a. Comparison for the two sets of 17O experimental parameters for NaIO4 shows that the quadrupole coupling parameters (CQ, ηQ) and indirect 1J(17O-127I) spin coupling constants are within

NMR spectra for the CT and STs are shown above Figure 1 (panels b−d). These simulations employed exactly the same optimized parameters (Table 1) as was obtained for the simulation in Figure 1b. The simulations in Figure 1 (panels c and d) clearly identify both origin and positions of the ssbs from the CT and STs. The distinct and unusual observations for the experimental and simulated AT 17O MAS spectra in Figure 1 (panels a and b, respectively) are the quite small “spikes/peaks” which appear on the flanks of both the CT and ST resonances. From the optimized fitting of the experimental spectra (e.g., Figure 1a), it is obvious that these “spikes/peaks” are caused by indirect scalar 1J(17O-127I) couplings with a magnitude of ∼500 Hz. To further explore the details of these 1J(17O-127I) spin couplings and resulting J-splittings, Figure 2 (panels a and b) show

Figure 2. Expansions of the centerbands for the CT regions presented in the two 112.8 MHz (19.6 T) experimental and simulated 17O MAS NMR spectra of NaIO4 in Figure 1 (panels a and b). (a) Expansion of the experimental spectrum. (b) Expansion of the simulated spectrum.

horizontal expansions for the CT centerband of the experimental and simulated spectra, respectively, of the corresponding central region spectra shown in Figure 1 (panels a and b). These horizontal expansions in Figure 2 illustrate that the two “horns” of the second order quadrupolar-broadened doublet-pattern (CQ = 11.19 MHz and ηQ = 0.066, see Table 1) appear like “teeth-on-a-saw” because of the 1J(17O-127I) spin 14437

DOI: 10.1021/acs.jpcc.5b03721 J. Phys. Chem. C 2015, 119, 14434−14442

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Figure 4. 112.8 MHz (19.6 T) experimental and simulated 17O MAS NMR spectra of KIO4 obtained for a spinning frequency νr = 17.84 kHz at AT and presented on a ppm scale corresponding to a total width of the spectra on a frequency scale of 150 kHz. The experimental spectrum was acquired using 32768 scans for 3 days and 19 h with a relaxation delay of 10 s. (a) Expansion for the centerband region of the experimental spectrum according to the two scales mentioned above. We note that the very narrow resonance at 0.0 ppm is caused by a minute presence of H217O in the dried sample, which confirms the 17O resonance frequency for our external reference sample of ordinary H217O water within ±1.0 ppm. (b) Optimized simulation, including the 17O CT and all STs, of the experimental spectrum in (a) and shown on the same frequency scales as in (a). The simulated spectrum used the optimized parameters listed in row 3 of Table 1.

Figure 3. 122.0 MHz (21.1 T) experimental (spin−echo; total spin− echo time of 64 μs) and optimized simulation 17O MAS NMR spectra of NaIO4 obtained for a spinning frequency νr = 31.25 kHz at AT. For comparison with the spectra in Figure 1, the spectra are presented on a ppm scale corresponding to a total width for the spectra on a frequency scale of 150 kHz, as used in Figure 1. The experimental spectrum was acquired using 2560 scans in 21.3 h for a relaxation delay of 30 s.

the error limits for each of the two experiments. Because of the high spinning rate employed at 21.1 T, the parameters obtained for the 17O CSA interaction are quite inaccurate. KIO4, 10% 17O-Enriched Sample. The experimental single-pulse (19.6 T; 112.8 MHz) and spin−echo (21.1 T; 122.0 MHz) 17O MAS NMR spectra for the ∼10% 17Oenriched sample of KIO4 exhibit almost identical spectral features as observed for the corresponding spectra shown in Figures 1−3 for NaIO4. For that reason only the most informative experimental and simulated single-pulse 19.6 T 17O MAS spectra are presented here in Figures 4 and 5 using a spinning frequency νr = 17.84 kHz. The analysis and optimized fitting to the experimental spectrum in Figure 4a follow the exact same procedures as described above in the section on the analysis and results for the spectra of NaIO4. Accordingly, we refrain to repeat this procedure here and refer the reader to the details in the above section. The result of the optimized fit to the experimental spectrum of KIO4 in Figure 4a is displayed in Figure 4b, and the resulting spectral parameters are summarized in Table 1. A most important difference between the 17O MAS spectra of NaIO4 and KIO4 is observed from the horizontal expansion for the CT centerband of the experimental and simulated spectra for KIO4 shown in Figure 5, when compared to the corresponding expansions in Figure 2 for NaIO4. The additional splitting for the expected “six-peak” splitting pattern for both two “horns” is much smaller in Figure 5 spectra (KIO4) compared to the larger splitting leading to a “sevenpeak” pattern in Figure 2 spectra (NaIO4). Thus, both expanded spectra for KIO4 in Figure 5 clearly show the “sixpeak” splitting with a further small/shoulder splitting for each of the total of 12 “six-peaks”, which corresponds to ηQ = 0.032 as opposed to the ηQ = 0.066 for NaIO4. These additional different small splitting in the 17O MAS spectra of NaIO4 and KIO4 partly explores the NMR crystallography for the two slightly different crystal structures of NaIO412 and KIO413 as will be discussed next in Discussion, NMR Crystallography, ADF, and CASTEP Calculations.

Figure 5. Expansions of the centerbands for the CT regions presented in the two 112.8 MHz (19.6 T) experimental and simulated 17O MAS NMR spectra of KIO4 in Figure 4 (panels a and b). (a) Expansion of the experimental spectrum. (b) Expansion of the simulated spectrum.

Discussion, NMR Crystallography, ADF, and CASTEP Calculations. In addition to the above results and data shown in Table 1, the optimized fitting of the experimental 17O MAS spectra for NaIO4 and KIO4 all lead to the intriguing result, that the effective dipolar coupling constant D′ and 1J(17O-127I) are of opposite sign. Because most solid-state NMR experiments are unable to either observe or even determine the sign of indirect J-couplings in solids, as opposed to the numerous methods available for this purpose in liquid-state NMR, we here elaborate on why this becomes possible for the present crystal 14438

DOI: 10.1021/acs.jpcc.5b03721 J. Phys. Chem. C 2015, 119, 14434−14442

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The Journal of Physical Chemistry C structures. This appears to be due to the NMR crystallography determined for the present samples, however, with two different options, of which one can be disregarded partly on experimental grounds due to an insufficient optimized fit of the experimental spectrum based on rms errors and partly because of unusual orientations of the 17O quadrupole and CSA tensors. This experimental finding is supported by CASTEP calculations of the tensor orientations (vide infra) and is in accordance with our ADF calculations of the principal elements of the J-tensors and thereby with the sign for 1J(17O-127I) (vide infra). As in our recent 17O VT MAS NMR study on the 1 17 J( O-187Re) coupling in two perrhenates (KReO4 and NH4ReO4),4 with analogous Scheelite-type structure (space group I41/a, Z = 4)13,29 as for the periodates, the molecular frame system for the IO4− tetrahedron has been selected with its z axis along the I−O bond and with the 127I quadupole principal z axis [Vzz(127I)] in the zx plane of the molecular frame. Thus, the orientation of the 127I quadupolar principal axis system (PAS) is given by the three angles (0,57,0) for NaIO412 and (0,56,0) for KIO413, while the D′ dipolar PAS is given by the three angles (0,0,0). Two sets of Euler angles describing the PAS orientation for the 17O quadrupole coupling [α(Q), β(Q), γ(Q)] and CSA [α(δσ), β(δσ), γ(δσ)] tensors relative to the definition of the molecular frame system have been used in the fitting procedure. Four of these angles have been fixed to zero, since only β(Q) and β(δσ) appear to be sensitive to the optimized fitting. This is exactly similar to the situation encountered in the analysis of the low-temperature 17 O MAS spectra of the perrhenates.4 Two widely different combinations of values for the pair of β(Q) and β(δσ) angles immediately became clear as possible candidates for a follow-up on two final optimized fits of the experimental periodate spectra, using these two different combinations of values for β(Q) and β(δσ). The first and most obvious combination is identical to the one, and only possible, found during the analysis of the 17O MAS spectra of the perrhenates4 and involves optimization of values in the region ∼0° for both β(Q) and β(δσ) [i.e., the principal axes Vzz(17O) and δzz(17O) of the PAS for these two tensors are almost along the I−O bond]. This full optimization for the two periodates involves all relevant parameters, including β(Q) ∼ β(δσ) ∼ 0°, for the experimental spectra and leads to the simulated spectra presented above in Figures 1−5 for both NaIO4 and KIO4. The corresponding spectral parameters are summarized in Table 1. The optimizations for both compounds lead to the conclusion that for β(Q) ∼ β(δσ) ∼ 0°, the indirect J-coupling and D′ are of opposite sign (i.e., D′ × J < 0). All attempts to find a minimum in the rms surface for J and D′ having the same sign (D′ × J > 0) were unsuccessful. At this stage, we here already note (vide infra) that the sign of the effective dipolar coupling D′ has been safely estimated to be negative (i.e., D′ < 0) and therefore used as such throughout the following discussion. In fact, for the optimum NaIO4 parameters obtained at 19.6 T and listed in Table 1, a sign-change in J (i.e., J < 0) increased the rms error by 12% for this parameter set. With this rms error and J < 0 as a starting point, a following optimization always converged to the parameter set with opposite sign for J and D′ (D′ × J < 0) shown in Table 1. To illustrate the changes in the 17O MAS spectrum of NaIO4 caused by the sign reversal in J, Figure 6 shows a comparison between the experimental spectrum (Figure 6a) and two simulated spectra using the parameter set in row 1 of Table 1 (Figure 6b, blue spectrum) and the same set with a negative sign for J (Figure 6b, red

Figure 6. Experimental and simulated 17O MAS NMR spectra obtained at 19.6 T of the centerband for the CT in NaIO4. The experimental spectrum is an expansion of the spectrum in Figure 1a. The two simulated spectra both used the optimized spectral parameters shown in Table 1 (row 1), except for the sign of the J coupling (i.e., J > 0 and J < 0, respectively). (a) Experimental spectrum. (b) Overlay of the two simulated spectra: J > 0 in blue and J < 0 in red. (c) Difference spectrum between the experimental spectrum (a) and the simulated spectrum for J > 0 in blue. (d) Difference spectrum between the experimental spectrum (a) and the simulated spectrum for J < 0 in red. (e) Difference spectrum between the two simulated spectra in blue and red, respectively.

spectrum). The spectra in Figure 6 clearly show how the sign reversal of the J coupling changes the intensity pattern near the left “horn” of the CT line shape. This effect can be rationalized in terms of the “effective” CSA for the six manifolds defined by the 127I spin states, mz = 5/2, 3/2, 1/2, −1/2, −3/2, and −5/2. For coincident PAS of the 17O CSA and D′ tensors, the “effective” CSA is given by [δσ + 2mz(127I)D′/ν0], where ν0 is the 17O resonance frequency.4 A sign reversal for 1J(17O-127I) reverses the order of the manifolds by swapping the “effective” CSA for the corresponding mz(127I) high- and low-frequency manifolds. The second, alternate solution with β(Q) ∼ β(δσ) ∼ 90°, resulting in a negative sign for the J coupling, is considered below. The effective dipolar coupling constant is defined as D′ = D − δJ/2, where the direct dipolar coupling constant is defined as D = (γIγSμ0ℏ)(8π2rIS3)−1 with I = 17O and S = 127I and δJ is the anisotropy in the indirect J spin−spin coupling as defined and used in our XSTARS,4 simulation/iterative fitting software. We note30 that alternatively ΔJ is also used in the literature to denote the anisotropy in the J coupling (see, for example, ref 30), and that the two conventions are related by the equation δJ = 2ΔJ/3 (i.e., similar to the two conventions also used in the literature for the chemical shift anisotropy, δσ and Δσ, where δσ = 2Δσ/3). From the r(17O-127I) bond lengths obtained from refinements of the crystal structures for NaIO412 and KIO413, r(17O-127I) = 1.775 and 1.762 Å, respectively, we obtain the two 14439

DOI: 10.1021/acs.jpcc.5b03721 J. Phys. Chem. C 2015, 119, 14434−14442

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The Journal of Physical Chemistry C direct dipolar couplings D = −587 Hz and D = −600 Hz for NaIO4 and KIO4, respectively. Generally, the magnitude of the anisotropy in the indirect spin−spin coupling (δJ) is small compared to D and/or the J coupling itself and usually it is assumed that δJ = 0. Thus, for a calculated direct dipolar coupling D ∼ −600 Hz, and an observed magnitude for the indirect J coupling 1J(17O-127I) ∼ 500 Hz for both NaIO4 and KIO4, we feel we are on safe ground in assuming that the effective dipolar coupling D′ = D − δJ/2 is negative, independent of the sign for δJ. Thus, combined with the above fascinating experimental result that D′ and 1J(17O-127I) are of opposite sign for both NaIO4 and KIO4, we conclude that 1J(17O-127I) is positive in sign for both compounds. These conclusions are fully supported following our ADF calculations with respect to the magnitudes and positive sign for 1J(17O-127I) and fairly large magnitudes and negative sign for δJ in both NaIO4 and KIO4, vide infra. We note that the positive sign determined here for 1J(17O-127I) is opposite to the negative sign determined in the same manner for 1J(17O-187Re).4 Furthermore, the positive sign and much larger magnitude of 1 17 J( O-127I) (∼ +500 Hz) results in an extreme large negative reduced coupling constant 1K(17O-127I) = (2π 1J(17O-127I))/ (γ17Oγ 127Iℏ) = −152.4 (10 20 NA−2 m−3), which is way outside the linear correlation observed recently between the reduced coupling constants 1K( 17O-M) and the atomic number for M, where M is a quadrupolar metal nucleus (e.g., M = 51V, 53Cr, 55 Mn, 95Mo, 99Tc, and 187Re). The 1J(17O-127I) spin coupling constants reported here are not only the first determined onebond J-coupling between 17O and a halogen atom but to our knowledge also the first determined one-bond coupling between 17O and a quadrupolar nonmetal nucleus along with its sign. Further extremely important results with respect to the NMR crystallography of NaIO4 and KIO4 arise from the optimized 17 O fitted data (Table 1) of the experimental 17O MAS spectra in Figures 1a and 2a and Figures 4a and 5a for the two (19.6 T) 17 O asymmetry parameters ηQ = 0.066 and ηQ = 0.032 in NaIO4 and KIO4, respectively. It turns out that the error limit for these ηQ values is < ± 0.005 and that the magnitude of ηQ is related to the magnitude of the additional splitting observed within the expected “six-peak” J-coupling patterns on the two “horns” for the second-order broadened CT. We point out that the “sevenpeak” pattern observed on the horns in the spectrum of NaIO4 (Figure 2) is due to the fact that the additional splitting (caused by ηQ = 0.066) is accidentally of similar magnitude as 1 17 J( O-127I) (i.e., ∼500 Hz). Assuming an ideal/perfect tetrahedron for the IO4− ion (i.e., ηQ = 0.000), a simulation using the 19.6 T parameters for NaIO4 listed in Table 1, but for ηQ = 0.000, turns the observed “seven-peak” pattern in Figure 2 into the expected “six-peak” J-coupling pattern. Thus, the two quite small, but very precise 17O asymmetry parameters ηQ = 0.066 and ηQ = 0.032 determined for NaIO4 and KIO4, respectively, show that the IO4− tetrahedron for NaIO4 and KIO4 are both slightly distorted. This is in complete agreement with the Scheelite-type crystal structures determined for NaIO4,12 KIO4,13 and other periodates (space group I41/ a)12,13 which show that the tetrahedra for the IO4− ions are slightly compressed in the crystal axis c direction. Thereby, the group of six tetrahedral angles, each equal to 109.47° for an ideal tetrahedron, splits into two groups. A group of two equalsized angles with an increased angle opening and a group of four equal-sized angles with a slight decrease of the angle

opening, both groups with respect to the ideal tetrahedral angle of 109.47°. The refined crystal structure for NaIO412 reports a value 114.05° for the group of two angles and a value 107.33° for the group of four tetrahedral angles. Since these angles were not reported from the refined crystal structure of KIO413, we have used this structure to calculate a value of 112.06° for the group of two angles and a value 108.19° for the group of four tetrahedral angles. Recognizing the increase for the tetrahedral angles (in the group of two angles) in going from KIO4 to NaIO4, accompanied by a corresponding increase for the ηQ values (or the corresponding additional splitting), and taking the disappearance of the additional splitting for ηQ = 0.000 for the ideal tetrahedron, the possibility of a linear correlation between the increase in tetrahedral angle and the ηQ values for these three points is looked into. Indeed, as shown in Figure 7,

Figure 7. Linear plot of the increase in the 17O quadrupole asymmetry parameter ηQ versus the increase in tetrahedral angle for the two large and equal-sized tetrahedral-angle openings upon compression of the IO4− tetrahedron along the crystal-axis c in NaIO4 and KIO4. As shown in the text an ideal tetrahedron with the coordinates (109.47°, 0.000) serves as the third (reference) point.

an excellent linear correlation (R = 0.991) is observed for the compression of the ideal tetrahedron in the region represented by the distortions determined for KIO4 and NaIO4. From the linear plot in Figure 7, we find that an increase by 1° (for the group of two equal-sized angles) in the ideal tetrahedral angle (109.47°) corresponds to increase in ηQ = 0.014. Finally, we believe that the experimental observation and determination of the extremely small and very precise ηQ values reported in this study would not have been possible without the presence of the large 1J(17O-127I) spin−spin coupling. This J coupling paved the way for the observation of the “teeth-on-asaw” pattern within the CT and thereby the resolution required for the present study in relation to solid-state NMR crystallography. We now return to the possible alternate solution which is observed for a ∼ 90° change in the orientation of both the 17O quadrupole and CSA tensor [i.e., for β(Q) ∼ β(δσ) ∼ 90°]. An optimized fit for these tensor orientations results in parameter values similar to the optimized parameters discussed and determined above for the NaIO4 data at 19.6 T in Table 1; however, most importantly with the result that J and D′ have the same sign (D′ × J > 0) (i.e., J < 0). With these conditions for β(Q) ∼ β(δσ) ∼ 90°, optimization of a fit for the experimental 17O MAS spectrum of NaIO4 at 19.6 T gives an rms error only slightly above (∼3%) the rms error for the optimized fit discussed above, corresponding to 14440

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Table 2. ADF and CASTEP Calculations of the 17O Quadrupole Coupling (CQ, ηQ), Chemical Shift Parameters (δσ, ησ, δiso), Effective Dipolar Coupling D′(17O-127I) = D − δJ/2, Isotropic Coupling J = 1J(17O-127I), and Its Anisotropy δJ in NaIO4 and KIO4 for Comparison with the Experimental 17O MAS NMR Data Reported in Table 1a sample AFD/CASTEP

CQ (MHz)

ηQ

δσ (ppm)

ησ

δiso (ppm)

J (Hz)

D′b (Hz)

δJ (Hz)

NaIO4/ADF KIO4/ADF NaIO4/CASTEP KIO4/CASTEP

−10.68 −10.51 −12.03 −11.69

0.07 0.04 0.08 0.04

178 167 180 173

0.17 0.10 0.24 0.11

278 261 374 357

449 461 − −

−470 −482 − −

−234 −236 − −

a

See text for the definitions of the relevant parameters used here and in our previous publications. bThe calculated D′ values are determined using the equation D′(17O-187Re) = D − δJ/2, employing the calculated values direct dipolar couplings D = −587 and −600 Hz for NaIO4 and KIO4, respectively, and their corresponding calculated anisotropic values δJ = −234 and −236 Hz shown in the last column of this table.

Table 3. ADF Calculated Values for the Three Principal Components of the Chemical Shift (δ) and Indirect Spin-Coupling (J) Tensors. Corresponding CASTEP Calculated Values Only for the Three Principal Components for the Chemical Shift (δ) Tensor. These Values for NaIO4 and KIO4 are used to calculate the Corresponding Anisotropic Parameters Shown in Table 2.a sample AFD/CASTEP

δxx (ppm)

δyy (ppm)

δzz (ppm)

Jxx (Hz)

Jyy (Hz)

Jzz (Hz)

NaIO4/ADF KIO4/ADF NaIO4/CASTEP KIO4/CASTEP

381.3 352.3 485.1 453.1

351.9 335.9 442.5 433.6

99.7 94.1 193.5 184.0

569.7 580.8 − −

561.4 576.5 − −

214.6 225.0 − −

a See text for the definitions of the relevant parameters used here and in our previous publications. It is noted that the ADF calculations used the isolated geometries for the two IO4− anions extracted from the crystal structures of NaIO412 and KIO413, while the CASTEP calculations used their full crystal structures.

β(Q) ∼ β(δσ) ∼ 0°. Thus, this new optimization for β(Q) ∼ β(δσ) ∼ 90° converges to a local, rather than to a global minimum on the rms surface. From a spectral simulation point of view, the small increase of ∼3% in rms error indicates, but does not definitively prove, that the parameter set shown for NaIO4 in Table 1 (row 1) with J > 0 is most likely the correct set. Furthermore, comparison of the orientations for the 17O quadrupole and CSA tensors [β(Q) ∼ β(δσ) ∼ 0°] are also in agreement with the results obtained for the perrhenates4 (identical crystal structure as for the periodates; space group I41/a) provided the parameter set shown in Table 1 for J > 0 is selected. Finally, the results of the ADF and CASTEP calculations to be presented below are in excellent agreement with the experimental data shown in Table 1. To confirm the results on the NMR crystallography of the two Scheelite structures for the IO4− ion obtained here from analysis of 17O solid-state MAS NMR spectra, some ADF7−10 and CASTEP11 calculations have been performed for both NaIO4 and KIO4 using the refined crystal structures for these compounds.12,13 The ADF calculations were performed for the two isolated IO4− anions whose geometries were extracted from the refined crystal structures of NaIO412 and KIO413. First of all, the tensor orientations resulting from both the CASTEP and ADF calculations confirm the orientations, β(Q) ∼ β(δσ) ∼ 0° for Vzz(17O) and δzz(17O), and with Vzz(127I) in the zx plane [β(127I) = −56°] along the crystallographic c axis, as discussed above for the molecular frame system for the IO4− tetrahedron and used in the optimized fitting of the present spectra and those recently for the perrhenate anions.4 The ADF and CASTEP calculated 17O spectral parameters for NaIO4 and KIO4 listed in Table 2 are all generally in very good agreement with the experimental values in Table 1. We note that the present version of our CASTEP software does not allow calculations of the J coupling data and therefore the J-coupling parameters reported here are only the results from ADF calculations of the principal components of the J tensor. To calculate the spectral parameters for the definitions of the CSA

and J tensor in the above eqs 1−6, the ADF and CASTEP calculated principal components in these tensors for both NaIO4 and KIO4 are summarized in Table 3. It is encouraging to observe that the positive sign and large magnitude determined experimentally for 1J(17O-127I) (approximately +500 Hz for both NaIO4 and KIO4) is fully confirmed by the ADF calculations. Similarly, the negative sign determined experimentally for 1J(17O-127I) (approximately −500 Hz), using the possible alternate tensor orientation β(Q) ∼ β(δσ) ∼ 90° as starting parameters for the optimized fitting leads to a slightly larger rms error. By changing the sign to positive for 1 17 J( O-127I) in a further optimization of all other parameters, this change to a fixed value 1J(17O-127I) = +500 Hz immediately changes the tensor orientation β(Q) ∼ β(δσ) to ∼0° in order to achieve an even lower rms error, as described above in detail. Finally, in conclusion, the ADF and CASTEP calculations in Table 3 fully support the unambiguous results reported here on the 17O solid-state NMR crystallography reported here for NaIO4 and KIO4. Conclusions. Analysis of RT 17O MAS NMR spectra of the periodate ion in NaIO4 and KIO4 has allowed determination of the magnitude and a positive sign for the indirect 1J(17O-127I) coupling [i.e., 1J(17O-127I) = +500 Hz]. In addition, the spectral analysis shows that the effective dipolar coupling (D′) and the indirect 1J(17O-127I) coupling (J) have the opposite sign (D′ × J < 0), which is in agreement with J > 0 since D′ has been safely estimated to be negative (D′ < 0). Furthermore, of two possible orientations for the quadrupole and CSA tensor, the spectral analysis (i.e., the NMR crystallography) favors the one where the molecular frame system for the IO4− tetrahedron has its z axis along the I−O bond and the principal axes Vzz(17O) and δzz(17O) of the PAS for both tensors are almost along the I−O bond. Finally, a further contribution to the NMR crystallography is observed from a precise linear correlation between very small changes for the 17O quadrupole asymmetry parameter (ηQ) and changes for the tetrahedral-angle (O−I−O) opening resulting from compression of the IO4− tetrahedron along the 14441

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(11) Clark, S. J.; Segall, M. D.; Pickard, C. J.; Hasnip, P. J.; Probert, M. I. J.; Refson, K.; Payne, M. C. First Principles Methods Using CASTEP. Z. Kristallogr. 2005, 220, 567−570. (12) Kalman, A.; Cruickshank, D. W. J. Refinement of the Structure of NaIO4. Acta Crystallogr. 1970, B26, 1782−1785. (13) De Waal, D.; Range, K. J. Strukturverfeinerung von Kaliumperiodat bei 297 und 150 K. Z. Naturforsch. 1996, 51b, 444−446. (14) Bielecki, A.; Burum, D. L. Temperature Dependence of 207Pb MAS Spectra of Solid Lead Nitrate. An Accurate, Sensitive Thermometer for Variable-Temperature MAS. J. Magn. Reson., Ser. A 1995, 116, 215−220. (15) Jakobsen, H. J. High-Speed MAS of Quadrupolar Nuclei in Solids. In Encyclopedia of Nuclear Magnetic Resonance; Grant, D. M., Harris, R. K., Eds.; Wiley: New York, 1995; Vol. 4, pp 2370−2379. (16) Bildsøe, H., Varian Manual, STARS (SpecTrum Analysis of Rotating Solids) User’s Guide, Publication No 87-195233-00, Rev. A0296, 1996. (17) Zaremba, S. K. Good Lattice Points, Discrepancy, and Numerical Integration. Annali di Matematica Pura ed Applicata 1966, 4−54, 325. (18) Conroy, H. Molecular Schrodinger Equation. VIII. A New Method for the Evaluation of Multidimensional Integrals. J. Chem. Phys. 1967, 47, 5307−5318. (19) Cheng, V. B.; Suzukawa, H. H., Jr.; Wolfsberg, M. Investigations of A Nonrandom Numerical Method for Multidimensional Integration. J. Chem. Phys. 1973, 59, 3992−3999. (20) Vosko, S. H.; Wilk, L.; Nusair, M. Accurate Spin-Dependent Electron Liquid Correlation Energies for Local Spin Density Calculations: A Critical Analysis. Can. J. Phys. 1980, 58, 1200−1211. (21) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865−3868. (22) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. Relativistic Regular Two-Component Hamiltonians. J. Chem. Phys. 1993, 99, 4597−4610. (23) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. Relativistic Total Energy Using Regular Approximations. J. Chem. Phys. 1994, 101, 9783−9792. (24) van Lenthe, E.; Snijders, J. G.; Baerends, E. J. The Zero-Order Regular Approximation for Relativistic Effects: The effect of SpinOrbit Coupling in Closed Shell Molecules. J. Chem. Phys. 1996, 105, 6505−6516. (25) van Lenthe, E.; van Leeuwen, R.; Baerends, E. J.; Snijders, J. G. Relativistic Regular Two-Component Hamiltonians. Int. J. Quantum Chem. 1996, 57, 281−293. (26) Monkhorst, H. J.; Pack, J. D. Special Points for Brillouin-Zone Integrations. Phys. Rev. B 1976, 13, 5188−5192. (27) Wasylishen, R. E.; Bryce, D. L. A Revised Experimental Absolute Magnetic Shielding Scale for Oxygen. J. Chem. Phys. 2002, 117, 10061−10066. (28) Wu, G.; Dong, S. High-Field 127I NMR of Solid Scheelite Structures: Periodates Revisited. Solid State Nucl. Magn. Reson. 2001, 20, 100−107. (29) Krebs, B.; Hasse, K.-D. Refinements of the Crystal Structures of KTcO4, KReO4 and OsO4. The Bond Lengths in Tetrahedral OxoAnions and Oxides of d0 Transition Metals. Acta Crystallogr. 1976, B32, 1334−1337. (30) Schurko, R. W.; Wasylishen, R. E.; Nelson, J. H. Effect of Cobalt-59 Self-Decoupling on the Solid-State 31P CP/MAS NMR Spectra of Cobaloximes. J. Phys. Chem. 1996, 100, 8057−8060.

crystal-axis c in NaIO4 and KIO4. The spectral parameters and NMR crystallography are excellently supported by ADF and CASTEP calculated data.

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The analysis and simulations of the acquired 17O MAS NMR spectra were performed at the Danish Instrument Centre for Solid-State NMR Spectroscopy, Aarhus University, DK-8000 Aarhus C, which is supported by two Danish National Research Councils. Thanks to Dr. Jacob Overgaard, Department of Chemistry, Aarhus University, for fruitful discussions and calculations of the tetrahedral angles in IO4− for KIO4. The 17O MAS NMR experiments were performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement DMR-1157490 and the State of Florida. The high spinning-frequency spin− echo spectra were obtained at the National Ultrahigh-Field NMR Facility for Solids (Ottawa, Ontario, Canada). G.W. thanks NSERC of Canada for funding and Dr. Victor Terskikh and Abouzar Toubaei for assistance in performing both experiments and calculations.

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REFERENCES

(1) NMR Crystallography; Harris, R. K.; Wasylishen, R. E.; Duer, M. J., Eds.; John Wiley & Sons, Inc.: Oxford, 2009. (2) Jakobsen, H. J.; Bildsøe, H.; Skibsted, J.; Brorson, M.; Hung, I.; Gan, Z. Synthesis of 17O- labeled Cs2WO4 and its Ambient- and LowTemperature Solid-State 17O MAS NMR Spectra. Inorg. Chem. 2011, 50, 7676−7684. (3) Jakobsen, H. J.; Bildsøe, H.; Brorson, M.; Gan, Z.; Hung, I. Quantitative Dynamics and Structure for Crystalline Cs2WO4 and KMnO4 Determined from High-Field 17O Variable-Temperature MAS NMR Experiments. J. Phys. Chem. C 2014, 118, 20639−20646. (4) Jakobsen, H. J.; Bildsøe, H.; Brorson, M.; Gan, Z.; Hung, I. Direct Observation of 17O-185/187Re 1J-coupling in Perrhenates by Solid-State 17 O VT MAS NMR: Temperature and Self-Decoupling Effects. J. Magn. Reson. 2013, 230, 98−110. (5) Hoering, T. C.; Ishimori, F. T.; MacDonald, H. O. The Oxygen Exchange Between Oxy-anions and Water. II. Chlorite, Chlorate and Perchlorate Ions. J. Am. Chem. Soc. 1958, 80, 3876−3879. (6) Bao, H.; Gu, B. Natural Perchlorate Has a Unique Oxygen Isotope Signature. Environ. Sci. Technol. 2004, 38, 5073−5077. (7) Amsterdam Density Functional Software ADF2009.01, SCM; Theoretical Chemistry; Vrije Universiteit: Amsterdam, The Netherlands, 2010, http://www.scm.com (accessed on June 10, 2015). (8) Te Velde, G.; Bickelhaupt, F. M.; Van Gisbergen, S. J. A.; Fonseca Guerra, C.; Baerends, E. J.; Snijders, J. G.; Ziegler, T. Chemistry with ADF. J. Comput. Chem. 2001, 22, 931−967. (9) Dickson, R. M.; Ziegler, T. NMR Spin-Spin Coupling Constants from Density Functional Theory with Slater-Type Basis Functions. J. Phys. Chem. 1996, 100, 5286−5290. (10) Autschbach, J.; Ziegler, T. Relativistic Computation of NMR Shieldings and Spin-Spin Coupling Constants. In Encyclopedia of Nuclear Magnetic Resonance; Grant, D. M., Harris, R. K., Eds.; Advances in NMR Spectroscopy; John Wiley & Sons, Chichester, 2002; Vol. 9, pp 306−322. 14442

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