## 2 Topical Research Areas Related to Ionic Liquids and the Contribution of Spiroammonium Compounds
### Organic Compounds as Structure-Directing Agents in Zeolite Synthesis
#### 2.6.2 Azoniaspiro Compounds as Structure-Directing Agents  
Azoniaspiro compounds have found applications as structural-directing agents in the synthesis of zeolites. The hydrothermal syntheses of zeolites have been carried out using the azoniaspiro compound--5-azoniaspiro-[4,4]-nonane as an SDA in a fluoride-free medium. Germanosilicate zeolites attract great attention due to the fact that a number of extra-large pore systems with ring sizes exceeding 12-membered rings have been reported. A phase-pure IWW-type zeolite was obtained after hydrothermal treatment at 175 \({}^{\circ}\)C for 3 days with an Si/Ge ratio of around 4.9 [Scheme 16a][181].  
When researching the use of azoniaspiro compounds as SDAs, the [PERSON] group focused their attention on substituted 6-azonia-spiro-[5,5]-undecanes; five different mono- and di-substituted azoniaspiro compounds **b**-**f** were obtained and used in the hydrothermal syntheses of zeolite (Scheme 16). Compounds **b**-**f** demonstrated relatively low selectivity; various topologies of zeolite structures were obtained: MTW, MOR, Beta, ERS-10, and defect-free MEL. MOR was obtained with all SDAs, and its formation has been favored by a  
Figure 16: Development of azoniaspiro compounds as the SDAs. Reproduced from [181, 182]. Copyright 2016 Elsevier.  
low SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) molar ratio in the reaction mixture. One of the azoniaspiro compounds--(l-ethyl-6-azonia-spiro-[5,5]-undecane yielded another interesting result: the crystallization of pure, defect-free zeolite MEL 9 [Scheme 16b] [182].  
Extra-large-pore germanosilicates with a UTL topology have been synthesized in basic media using a wide variety of sterically loaded spiroazonia compounds (**a-m**) as the SDAs. The composition of the reaction mixture and nature of the SDAs (structure, hydrophilicity/hydrophobicity balance, rigidity, and pKa) influenced phase selectivity and the degree of crystallinity in the UTL structure (Scheme 17) [183].  
The optimum synthesis time was considered to be 3-7 days at a Si/Ge ratio of 2 and (Si + Ge)/SDA molar ratios of 1.7-6. Zeolite with UTL structure shows very high thermal stability; the structure does not collapse after calcination, even at 1000 \({}^{\circ}\)C. The micropore volume of the best crystals is 0.21-0.23 cm\({}^{3}\)/g, and the micropore diameter is \(\sim\)1.0 nm.  
In this work, the following selection criteria for organic molecules for use as potential SDAs have been used:  
(1) SDA organic molecule should contain one or two quaternary N atoms and have a C/N ratio in the range of 10-16. (2) An SDA molecule should possess sufficient rigidity. It is desirable that its structure should include two or more five- or six-membered aliphatic hydrocarbon rings. The spiro-structure, especially with a charged N atom in place of a joining of two rings, as well as the presence of benzene rings, is useful. (3) An SDA molecule should possess optimum hydrophobicity (log P = \(-\)1.8 and \(-\)0.6). (4) An SDA should possess sufficiently high stability under the hydrothermal synthesis of zeolites. (5) The kinetic diameter of the SDA molecule should be within 7-15 A.  
It has been stressed that zeolites have a more perfect structure and higher micropore volume when they are crystallized from the reaction mixtures, having higher SDA template contents. In contrast, when using the large SDA molecules (SDAc, SDAg, SDAj, and SDAk), it is necessary to decrease the template contents (Si + Ge)/SDA.