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The synthesis or preparation of inorganic substances is an important part of inorganic chemistry. It is very necessary to master the basic preparation reactions and the synthesis methods of typical substances. There are a wide variety of inorganic compounds, and the methods for preparing different types of compounds vary greatly. The same substance often has multiple preparation methods, especially for many new complexes. With the development of modern technology, some special preparation techniques and methods have emerged, and the choice of method depends on the system. Usually, finding a reaction that can produce the desired substance in high yields is just the beginning; the next step is to find a suitable method, and one also has to consider how to separate the product from the reaction mixture. Common general preparation methods include: using double displacement reactions. A double displacement reaction is a reaction in which two compounds exchange components in solution to form two other compounds. When it is used to prepare compounds, if the product is a precipitate or a gas, the product can be easily obtained by separating the precipitate or collecting the gas. If the product is also soluble in water, then crystallization or recrystallization (purification) must be used to obtain it. The main operations in this preparation method include evaporation and concentration of the solution, crystallization, recrystallization, filtration, and washing. For example: producing KNO3 from KCl and NaNO3, producing Na2CO3 from NaCl and NH4HCO3, etc. Prepared from ore. Ore refers to natural substances that have mining value under modern technological conditions. Ore of metal elements can generally be classified into: free metals and intermetallic compounds, sulfides, halides, oxides, and oxoacids. To prepare inorganic substances from ore, it is first necessary to refine the ore, that is, to separate the useful parts of the ore from the waste slag, in order to improve the quality of the ore. The purification process can involve simple manual sorting based on the physical properties of the ore, such as color, luster, and shape. It can also rely on the difference in density between the ore and the slag; in this case, the slag is removed by washing with water, or magnetic iron ore is separated from non-magnetic slag using electromagnetic methods. After purification, the ore is subjected to treatments such as acid (alkali) melting, leaching, oxidation or reduction, and calcination to produce the desired substance. When producing KMnO4 from pyrolusite (MnO2·xH2O), the liquid is first treated with KClO3 in an alkaline medium. By taking advantage of the difference in solubility, FeSO4·7H2O crystals are removed; then TiOSO4 is hydrolyzed at high temperature to yield metatitanic acid, which is subsequently calcined to produce titanium dioxide. Preparation of intermolecular compounds. Intermolecular compounds are compounds formed by the combination of simple compound molecules in a specific stoichiometric ratio. Its range is very wide, including hydrates such as copper sulfate pentahydrate CuSO4·5H2O; ammine complexes such as calcium chloride octaammine CaCl2·8NH3; double salts such as carnallite KCl·MgCl2·6H2O and alum K2SO4·Al2(SO4)3·24H2O; coordination compounds such as K4[Fe(CN)6]; and organic molecule adducts such as CaCl2·4C2H5OH, among others. The process of preparing intermolecular compounds is relatively simple. The general process involves the interaction of simple compounds in an aqueous solution; by evaporating to concentrate the solution, cooling it, inducing crystallization, filtering, washing, and drying the crystals, the product is obtained. For example, the preparation of Moore’s salts and the preparation of sodium hexanitrito-cobalt(III). Some compounds are highly susceptible to hydrolysis; therefore, their preparation requires special conditions – the reactants as well as the products must not come into contact with water or water vapor. The production equipment must be sealed, and the raw materials as well as the entire setup need to have water removed thoroughly. For example, when preparing tin tetrachloride SnCl4 using chlorine gas and tin particles, not only must the entire equipment be airtight, but the chlorine gas used must also be purified and dried. The resulting product SnCl4 should also be stored properly to prevent hydrolysis. There are a wide variety of complexes, and numerous methods exist for their preparation. Common synthesis methods and reactions include (1) simple addition reactions, in which a Lewis acid reacts with a Lewis base to directly produce a complex. (2) Substitution reaction: Many complexes are obtained by substituting water molecules in hydrated ions. In terms of substitution reactions, complexes can be divided into active complexes and inert complexes. Those complexes in which the ligands can be rapidly replaced by other ligands are called active complexes, whereas those in which ligand substitution occurs slowly are called inert complexes. Many substitution reactions still need to be carried out in non-aqueous solvents. (3) Redox reactions: low-valent complexes can be oxidized to high-valent complexes, and high-valent complexes can be reduced to low-valent complexes. (4) Thermal decomposition: By controlling the heating process, certain complexes can be converted into other complexes. Additionally, some special complexes have distinct preparation reactions and methods, such as carbonyl complexes and organometallic complexes.