HEXAMERIC LITHIUM PHENOLATE - CRYSTAL-STRUCTURES AND LI-7 QUADRUPOLE COUPLING IN SOLID AND SOLUTION PHASES
HEXAMERIC LITHIUM PHENOLATE - CRYSTAL-STRUCTURES AND LI-7 QUADRUPOLE COUPLING IN SOLID AND SOLUTION PHASES
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DOI：
10.1021/ja00067a046
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发表时间：
1993-07-14
影响因子：
15
通讯作者：
NICHOLS, MA
中科院分区：
文献类型：
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作者：
JACKMAN, LM;CIZMECIYAN, D;NICHOLS, MA
而苯酚锂在二氧戊环中作为相当数量的六聚体和四聚体的混合物以及少量的较少聚集的物质共存，在THF中主要的物质是四聚体。已从THF和THF/己烷溶液中获得两种晶体形式的苯酚锂，X射线晶体学研究表明，它们由非常相似的六方棱柱形苯酚锂六聚体组成，每个锂阳离子与一个THF分子结合。对其中一个晶体样品的粉末谱进行了线形分析，得到了Li-7核四极耦合常数（QCC = e_2Qq（zz）/h = 67 ± 1 kHz）和非对称性参数（η = 0.77 ± 0.05）。质子去偶被用来去除H-1/Li-7偶极-偶极相互作用，并且用Li-6稀释的样品被用来估计Li-7/Li-7相互作用对线形的贡献。这些数据给出了四极分裂常数[QSC =（1 + η 2/3）1/2（e2 Qq（zz/h）]的值（73 kHz），与从自旋-晶格弛豫数据对二氧戊环中的六聚苯酚锂测定的值（72 +/- 10 kHz）一致。四聚物在THF和二氧戊环中的QSC值分别为46 +/- 0.5和59 +/- 6 kHz。CP-MAS C-13 NMR光谱对于表征聚集体的固体样品具有有限的价值。
Whereas lithium phenolate in dioxolane coexists as a mixture of comparable amounts of a hexamer and tetramer, together with minor amounts of less aggregated species, in THF the predominant species is the tetramer. Two crystalline forms of lithium phenolate have been obtained from THF and THF/hexane solutions, and X-ray crystallographic studies show that they consist of very similar hexagonal prismatic hexamers of lithium phenolate with one THF molecule bound to each lithium cation. The Li-7 nuclear quadrupole coupling constant (QCC = e2Qq(zz)/h = 67 +/- 1 kHz) and the asymmetry parameter (eta = 0.77 +/- 0.05) have been obtained from line shape analysis of the powder spectrum of one of the crystalline samples. Proton decoupling was used to remove H-1/Li-7 dipole-dipole interactions, and samples diluted with Li-6 were employed to estimate the contribution of the Li-7/Li-7 interaction to the line shape. These data give a value (73 kHz) for the quadrupole splitting constant [QSC = (1 + eta2/3)1/2(e2Qq(zz/h)] in agreement with that (72 +/- 10 kHz) determined for hexameric lithium phenolate in dioxolane from spin-lattice relaxation data. The values of QSC for the tetrameric species in THF and dioxolane are 46 +/- 0.5 and 59 +/- 6 kHz, respectively. CP-MAS C-13 NMR spectroscopy is of limited value for characterizing solid samples of the aggregates.