Triple-Quantum Two-Dimensional ²⁷Al Magic-Angle Spinning Nuclear Magnetic Resonance Spectroscopic Study of Aluminosilicate and Aluminate Crystals and Glasses

Abstract

A new two-dimensional magic-angle spinning NMR experiment 1,2 using multiple-quantum coherences of half-integer quadrupolar nuclei was used to study 27 Al sites in crystalline samples of leucite (KAlSi 2 O 6 ), anorthite (CaAl 2 Si 2 O 8 ), and kyanite (Al 2 SiO 5 ), as well as CaAl 2 Si 2 O 8 glass and a magnesium aluminoborate glass. In the crystals, multiple sites are partially resolved and new results for isotropic chemical shifts and quadrupolar parameters are derived, using data collected at a single magnetic field. Data for both leucite and anorthite are consistent with previous results that correlate chemical shifts with mean intertetrahedral bond angle. Signal can be obtained from sites with quadrupolar coupling constants as large as 9 MHz, but intensities are reduced. In the aluminoborate glass, peaks for sites with different Al coordination numbers are well separated. The lack of such features in CaAl 2 Si 2 O 8 glass rules out the presence of significant quantities of AlO 5 and AlO 6 groups.

Two-Dimensional Multiple-Quantum MAS NMR of Quadrupolar Nuclei: A Comparison of Methods

“…Three long narrow ridges can be identified (the modulated split-t 1 experiment (Figs. 12a and 14b for spins isotropic shifts are marked with arrows in the F 1 dimension) I Å 3/2 and 5/2, respectively) will often be better than that and, as two of the C Q values for kyanite are very similar of the amplitude-modulated whole-echo experiment, since (14), these correspond to the four crystallographically inthe latter, despite its theoretical 2 sensitivity advantage, equivalent sites.…”

“…In experiments containing spin echoes, the spinin which the signals from the echo and antiecho experiments are shifted in t 2 by forming a spin echo using a selective inver-echo interval was set equal to an integral number of rotor periods (4,14). The phase cycling used for each different pulse sion pulse on the central transition (4).…”

“…As discussed in Refs. (4,14), shearing the data set reduces the spectral width in F 1 by a factor, using the notation of Table 1, of lineshape. Figures 7d and 7g correspond to a summation of Gaussian lineshapes along the diagonal F 1 Å 0F 2 , such that where the flip angle of the p Å {3 to p Å 01 conversion the projection onto an axis parallel to the ridge is a typical pulse is varied.…”

Composite Pulse Excitation Schemes for MQMAS NMR of Half-Integer Quadrupolar Spins

“…The resulting 2D MQMAS technique NMR is a well-established tool for analyzing many strucconsequently provides a simple approach to high resolution tural and dynamic problems of polycrystalline solids (1,2). quadrupolar NMR spectroscopy in solids, whose capabilities Crucial to the success of these applications are coherent have already been demonstrated with several practical applimanipulations which allow one to discriminate among sigcations on different nuclei (17)(18)(19)(20)(21). In view of the potential nals arising from inequivalent chemical sites despite the aniusefulness of this approach, considerable efforts have also sotropic character of spin interactions.…”

A Solid-State NMR Study of Coordination Transformation in Amorphous Aluminum Oxide: Implication for Crystallization of Magma Ocean

“…3QMAS NMR 분광분석은 빠른 시료의 회전속 도와 다중 양자 결맞음(multiple quantum coherences)을 이용하여 사중극자 상호작용의 2차 섭동항 (second-order quadrupolar broadening)에 의한 해 상도 저하를 억제하는 기술이다 (Frydman and Harwood, 1995;Baltisberger et al, 1996). 분석 시 여 러 개의 라디오주파수 펄스로 구성된 펄스시퀀스 를 이용하고 펄스들 간의 간격(interval, t 1 )을 변화 시키며 실험을 진행하여, 기존의 MAS NMR 분석 에서 얻어지는 시간변수(data acquisition, t 2 ) 외에 하나의 추가적인 시간변수 t 1 가 존재하게 된다 (Levitt, 2001).…”