Radha A V, Kamath P Vishnu, Shivakumara C
Department of Chemistry, Central College, Bangalore University, Bangalore 560 001, India.
J Phys Chem B. 2007 Apr 5;111(13):3411-8. doi: 10.1021/jp0684170. Epub 2007 Mar 9.
Carbonate and chloride ions mediate an ordered stacking of metal hydroxide slabs to yield ordered layered double hydroxides (LDHs) of Zn with Al, by virtue of their ability to occupy crystallographically well-defined interlayer sites. Other anions such as ClO(4)- (T(d)), BrO(3)- (C(3v)), and NO(3)- (coordination symmetry C(2v)) whose symmetry does not match the symmetry of the interlayer sites (D(3h) or O(h)) introduce a significant number of stacking faults, leading to turbostratic disorder. SO(4)(2-) ions (coordination symmetry C(3v)) alter the long-range stacking of the metal hydroxide slabs to nucleate a different polytype. The degree of disorder is also affected by the method of synthesis. Anion-exchange reactions yield a solid with a greater degree of order if the incoming ion is a CO3(2-) or Cl-. Incoming NO(3)- ions yield an interstratified phase, whereas incoming SO(4)(2-) ions generate turbostratic disorder. Conservation or its converse, elimination, of stacking disorders during anion exchange is the net result of several competing factors such as (i) the orientation of the hydroxyl groups in the interlayer region, (ii) the symmetry of the interlayer sites, (iii) the symmetry of the incoming ion, and (iv) the configuration of the anion. These short-range interactions ultimately affect the long-range stacking order or "crystallinity" of the LDH.
碳酸根离子和氯离子凭借其占据晶体学上定义明确的层间位点的能力，介导金属氢氧化物板有序堆叠，从而生成锌与铝的有序层状双氢氧化物（LDH）。其他阴离子，如对称性与层间位点（D(3h) 或 O(h)）不匹配的 ClO(4)-（T(d)）、BrO(3)-（C(3v)）和 NO(3)-（配位对称性 C(2v)），会引入大量堆垛层错，导致层错无序。SO(4)(2-) 离子（配位对称性 C(3v)）会改变金属氢氧化物板的长程堆叠，形成不同的多型体。无序程度还受合成方法的影响。如果进入的离子是 CO3(2-) 或 Cl-，阴离子交换反应会生成有序程度更高的固体。进入的 NO(3)- 离子会产生层间互层相，而进入的 SO(4)(2-) 离子会导致层错无序。阴离子交换过程中堆垛无序的保留或相反的消除，是几个竞争因素的净结果，例如（i）层间区域羟基的取向，（ii）层间位点的对称性，（iii）进入离子的对称性，以及（iv）阴离子的构型。这些短程相互作用最终会影响 LDH 的长程堆叠顺序或“结晶度”。
