Polytype Selection by Intercalated Anions: Design and Synthesis of the 3R2 Polytype of the Layered Double Hydroxide of Zn and Al

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• 作者：S. Radha ; S. V. Prasanna ; P. Vishnu Kamath
• 刊名：Crystal Growth & Design
• 出版年：2011
• 出版时间：June 1, 2011
• 年：2011
• 卷：11
• 期：6
• 页码：2287-2293
• 全文大小：842K
• 年卷期：v.11,no.6(June 1, 2011)
• ISSN：1528-7505

文摘

The layered double hydroxides are obtained by the stacking of metal hydroxide layers one above another. The stacking sequence is determined by the molecular symmetry of the intercalated anion. Anions select for those stacking sequences which provide interlayer sites having a local symmetry compatible with their own molecular symmetry. Oxoanions, XO₃p>n鈥?/sup> (X = S, I), are unique in that their molecular symmetry, C_3v, is compatible with two different polytypes of rhombohedral symmetry. The SO₃p>2鈥?/sup> ion selects for the more ubiquitous 3R₁ polytype, whereas the IO₃p>鈥?/sup> ion selects for the much rarer 3R₂ polytype. Structure refinement shows that neither anion departs significantly from the structure of the free species on intercalation. The higher charge-to-size ratio of the SO₃p>2鈥?/sup> ion compared to the IO₃p>鈥?/sup> ion and its consequent stronger basicity is responsible for the nucleation of the 3R₁ polytype, wherein the trigonal prismatic interlayer sites facilitate the superior hydrogen bonding capacity of the SO₃p>2鈥?/sup> ion. The poorer basicity of the IO₃p>鈥?/sup> ion and its consequent poorer proclivity to form hydrogen bonds select for the 3R₂ polytype wherein the IO₃p>鈥?/sup> ion is lodged in interlayer sites of octahedral symmetry.