# Synthesis methods of inorganic materials

On our exams we are asked to determine which synthesis method is best suited for a given compound. We have discussed direct synthesis methods such as high temp. and ampull, and indirect synthesis methods such as solvothermal, sol-gel, and ion exchange.

I thought that the direct high temperature synthesis was mostly used for compounds with three or more elements such as $$\ce{BaTiO3}$$. However, in our exam the compound $$\ce{Fe3O4}$$ is said to be synthesized by the direct high temperature method.

For example, one question states:

Propose and motivate two methods (each) of synthesis of $$\ce{NaAlSiO4}$$ and $$\ce{Cu(CN)(pyr)2}$$

I believe one method for $$\ce{NaAlSiO4}$$ should be direct high temp. because that method is applicable for aluminosilicates but have no idea what the second one could be. Is there a specific way to determine the synthesis methods of different compounds just by looking at them?

All help is truly appreciated!

• I'd say, no, it's impossible to say which method exactly would work the best, you can only make general assumptions such as organic ligands or hydroxo-salts won't survive a high-temperature synthesis. Metal oxides, on the other hand, can be synthesized by a variety of low- and high-temp methods and their combinations (see e.g. Pechini method). – andselisk Dec 27 '19 at 12:26
• The synthesis method depends on your preferred starting material. What do you propose for both of them? – Karl Dec 27 '19 at 12:27
• @Karl For Cu(CN)(pyr)$_2$ I don't really have any idea on what the methods could be. For NaAlSiO$_4$ the starting materials would be NaAlO$_2$ and SiO$_2$. How does that help determine the method? – katara Dec 27 '19 at 12:36
• Your list of methods has a few missing, e.g. precipitation from solution and transport reaction in a temperature gradient. – Karl Dec 27 '19 at 12:38
• Yup. Both NaAlO2 and SiO2 have very high melting points. Do you have an oven and crucible that goes that high? I say no. So you need to get the necessary temperature down. Ideas? And the starting materials for the other one are rather obvious, think simple! – Karl Dec 27 '19 at 12:48