Continued on the table  Common precious metal chloride complex anion and features element Valence Electronic configuration Main complex Standard oxidation reduction potential / V Complex space configuration 　 IV D5 IrCl 6 2- IrCl 6 2- /IrCl 6 3- 0.93 Octahedron Os III D5 Os ( H 2 O ) Cl 5 2- OsCl 6 3- /Os 0.71 Octahedron 　 　 　 OsCl 6 3- 　 　 　 IV D4 OsCl 6 2- OsCl 6 2- /OsCl 6 3- 0.85 Octahedron 　 　 　 Os ( H 2 O ) Cl 5- 　 　 　 IV 　 OsO 2 Cl 2- 　 　 Ru III D5 Ru ( H 2 O ) Cl 5 2- RuCl 6 3- /Ru 0.6 Octahedron 　 　 　 RuCl 6 3- 　 　 　 IV D4 Ru 2 O ( H 2 O ) 2Cl 8 2- RuCl 6 2- /RuCl 6 3- 1.2 Octahedron 　 　 　 　 　 　 　 These anions in the acidic solution form dissociable weak acids with the hydrogen cations and both have a fresh enamel color from yellow to red. The most important factors affecting the stability of these chlorine complexes are the oxidation valence state, the Rh(III) and Ir(III) complexes are the most stable, and the Pt(II) and Pd(II) complexes are the most unstable. Ir(IV) is easily reduced to Ir(III) and reacts quickly. The reaction rate of Pt(IV) reduction to Pt(II) is very slow. In addition, conditions such as acidity, chloride ion concentration, temperature, standing time, and oxidation-reduction potential of the solution are also important factors affecting the stability. Under different conditions, the chlorine anion will undergo hydration, hydroxylation, acid dissociation of hydrated ions and other reactions, and will be converted into chlorine-hydrated, chloro-water-hydroxy complexes of various compositions, and their properties will also change accordingly. [next]
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Recombinant platinum group metals (osmium, iridium, platinum), group lighter than platinum group metal (ruthenium, rhodium, palladium) and thermodynamic stability of the reaction of the same valence compound or complex of large kinetically inert, i.e. Os (â…£)> Ru(IV), Ir(IV)>Rh(N), Ir(III)>Ir(III), Pt(IV)>Pd(IV), such as (OsCl 6 ) 2- ratio (RuCl 6 ) 2- stabilized The latter is easily reduced to a low price; (IrCl 6 ) 2- ratio (RhCl 6 ) 2- is stable, the former can be stably present in an acidic solution, and the latter can only exist under a strong oxidation condition having an oxidation potential greater than 1.8V. And it is easy to be reduced to low price; (IrCl 6 ) 3- ratio (RhCl 6 ) 3- stabilized, the latter is easily reduced from solution to metal by negatively charged metals (such as zinc , magnesium , iron , aluminum, etc.) The former is more difficult; (PtCl 6 ) 2- ratio (PdCl 6 ) 2- is stable, the latter is automatically reduced to a low price when boiled in solution, but the former cannot; (PtCl 4 ) 2- ratio (PdCl 4 ) 2- Stable, they are reduced to metal at a faster rate than the former. In addition, the above laws are also observed in the neutralization hydrolysis and hydration reactions.
2. Nitrite complexes Adding excess NaNO 2 or KNO 2 to a chlorine complex solution of a platinum group metal (except ruthenium) can form nitroso complexes of different compositions. NO 2 - substituted Cl - and easily substituted for each other. The substitution reaction is accompanied by a reduction, and the final oxidation state of the central ion is expressed as a low state. A change in the amount of the two ligands in the complex results in a change in the nature of the complex. Taking the color change of the ruthenium complex as an example, IrCl 6 3- yellow green → [IrCl 4 (NO 2 ) 2 3- ] golden yellow → [IrCl 2 (NO 2 ) 4 3- ] light yellow → [Ir(NO 2 ) 6 3- ] Colorless. Therefore, in a system in which two ligands coexist, a complete nitroso complex cannot exist.
Most noble metal nitroso complexes appear white, while aqueous solutions are colorless. Only a few are yellow to green. The sodium salt is soluble in water, and the solubility of the potassium salt and the ammonium salt is small. Almost insoluble in KCl and NH 4 Cl solutions.
When NO and NO 2 are present in the nitro complex structure of ruthenium, such as [RuNO(OH)(NO 2 ) 4 ] 2- , the salt is orange, and is easily soluble in water and alcohol. Even its potassium salt is easily soluble in alcohol. Reaction with hydrochloric acid, converted to the mixed ligand complexes [RuNOCI 5] 2-, the sodium, potassium, rubidium, cesium salt are all stable pink crystalline sparingly soluble in water.
Nitrite complexes of platinum, palladium, rhodium, iridium, sodium Na 2 Pt(NO 2 ) 4 , Na 2 Pd(NO 2 ) 4 , Na 3 Rh(NO 2 ) 6 , Na 3 Ir(NO 2 ) 6 They are all soluble in water and more stable in terms of hydrolysis properties than the corresponding chlorine complex sodium salt. When heated to boil and neutralized with an alkali solution, the platinum, rhodium complex salt does not undergo a hydrolysis reaction at pH 12-14, and the palladium salt at pH 8-10. This feature allows the separation of precious metals.
The metal sulfide can be precipitated from a solution of a soluble nitrite complex of platinum, palladium or rhodium with sodium sulfide. But it cannot precipitate cockroaches.
Ammonium chloride is added to the aqueous solution of hexanitroso-sodium salt in hydrazine. After repeated exchange of ammonium and sodium ions, it is finally converted into (NH 4 ) 3 Rh(NO 2 ) 6 white precipitate, which is insoluble in cold water and ethanol. Soluble in hot water, insoluble in ammonium chloride. This property can be used for the separation of rhodium from other precious metals and the refining and purification of rhodium. [next]
The nitrite and sodium salt of hydrazine are treated in the same manner as above, and the ammonium sodium mixed salt is slightly soluble in water but soluble in a 10% ammonium chloride solution. The concentration of ammonium chloride was continuously increased, and finally it was converted into a white precipitate (NH 4 ) 3 Ir(NO 2 ) 6 which was slightly soluble in water and insoluble in ammonium chloride.
3. Ammonia complex Ag + and ammonia form cationic complexes AgNH 3 + and Ag (NH 3 ) 2 + , AgCl 2 - and ammonia form soluble AgCl 2 (NH 3 ) 2 .
Ammonia replaces Cl - from the chlorine complex, and depending on the coordination number of NH 3 , many complexes with different structures and different solubility properties can be formed. The nature of the ammonia complex is more stable than the corresponding chlorine complex. It is difficult to precipitate metal sulfide from the ammonia complex even with sodium sulfide.
The ammonia-containing complex of Pt(II) has the formula: [Pt(NH 3 ) n Cl 4-n ] n-2 . Reaction with NH 4 OH and Na 2 PtCl 4 produces a bright yellow cis-dichlorodiamine platinum [Pt(NH 3 ) 2 Cl 2 ] precipitate, which is known as the cisplatin anticancer drug. However, it is not easily soluble in water and has a solubility of only 0.25% in water at 25 °C. However, complexes containing 1, 3 or 4 ammonia are readily soluble in water. The tetraammine complex R(NH 3 ) 4 Cl 2 is reacted with concentrated hydrochloric acid and boiled to precipitate a bright yellow trans-dichlorodiamine platinum precipitate.
The chlorine-containing anion of palladium reacts with ammonia to precipitate a water-insoluble rose salt Pd(NH 3 ) 4 •PdCl 4 (called a wolf salt), but continues to add ammonia and heat to convert it into a soluble colorless salt Pd. (NH 3 ) 4 Cl 2 . The addition of hydrochloric acid was again converted to a yellow precipitate of poorly soluble p-dichlorodiamine palladium [Pd(NH 3 ) 2 Cl 2 ]. The method of refining palladium established using this property has been used until now.
The trivalent ammonia chloride complex, such as Rh(NH 3 ) 3 Cl 3 and [Rh(NH 3 ) 5 CI]Cl 2 , is hardly soluble in water. The former has a solubility of only 0.828% in water at 25 °C.
Bismuth also forms a hydrazine-like ammonia complex, such as Ir(NH 3 ) 3 Cl 3 , which is poorly soluble in water. However, [Ir(NH 3 )5Cl]Cl 3 is easily soluble in water.
4. Thiourea Complex Silver and thiourea form soluble AgSC(NH 2 ) 2 and Ag 2 SC(NH 2 ) 2 complexes for extracting silver from ore.
Platinum group metals and thiourea also form a series of complexes, characterized in that the central ions are reduced to a low cost with the coordination process, and finally converted into sulfide precipitates in an acidic solution. Relatively speaking, the platinum thiourea complex is relatively stable, such as the yellow complex Pt[4SC(NH 2 ) 2 ]Cl 2 is soluble in water and can be concentrated and crystallized. However, Pd[4SC(NH 2 ) 2 ]Cl 2 is soluble in water and easily decomposes into palladium sulfide precipitate upon heating.
In sulfuric acid or an alkali metal sulfate solution, Cl - in the above tetrathiourea complex can be substituted by SO 4 2- and precipitate a poorly water-soluble crystal Pt[4SC(NH 2 ) 2 ]SO 4 (yellow white And Pd[4SC(NH 2 ) 2 ]SO 4 , which are soluble in concentrated sulfuric acid. After dilution, the crystals were re-precipitated.