Compounds Cu(I).
These compounds can be prepared by Cu(II) reduction. Cu2О is formed at the action of hydrazine, hydroxylamine, aldehydes, glucose on Cu(ОH)2:.
4Cu(ОH)2 + N2H4 = 2Cu2O + N2 + 6H2O
or 4CuO 2Cu2O + О2
2CuI +2NaOH = Cu2O + H2O + 2NaI
CuOН does not exist. It decomposes immediately at the moment of liberation on Cu2O and H2O. Cu2O has predominately basic properties. It react with acids::
Cu2O + 4HCl = 2H[CuCl2] + H2O
Cu2O + H2SO4 = Cu + CuSO4 + H2O.
Salts Cu(І) can be obtained by Cu(II) reduction:
2CuSO4 + 2NaCl + SO2 + 2H2O = 2CuCl¯ + Na2SO4 + 2H2SO4
CuCl2 + 2HCl + Cu = 2H[CuCl2] (+H2O) = 2HCl + 2CuCl¯
CuI formation is a result of redox process that proceeds quantitavely:
2CuSO4 + 4KI = 2CuI¯ + I2 + 2K2SO4
Salts Cu(I) are colourless that are usually insoluble in water but at the action of ammonia and some other ligands can form soluble complexes:
CuCl + 2NH3 = [Cu(NH3)2]Cl
CuCl + HCl = H[CuCl2]
Complexes of Cu(I) with monodental ligands with coordination number 2 have maximal stability (for instance, [Cu(NH3)2]+, [CuCl2]-, [Cu(СN)2]-) and have linear configuration (Cl-Cu-Cl)-. Complexes with coordination number 4 are tetrahedral. Some complexes are oxidized by oxygen:
4[Cu(NH3)2]+ + 4NH3 + 4NH4+ + O2 = 4[Cu(NH3)4]2+ + H2O
This reaction is used to absorb oxygen from gaseous mixtures.
In general, equilibrium 2Cu+ Cu2+ + Cu is easily displaced depending on conditions. The presence of I-, CN- that form stable compounds with Cu(I) displaces equilibrium to Cu+ formation. The presence of SO42-, ClO4- shows the contrary action.
Compounds Cu(III). These compounds are obtained by oxidation of Cu(II). The deep red Cu2О3 forms at the action of Na2O2 or K2S2O8 on Cu(ОН)2 or Na2[Cu(ОH)4]:
2Na2[Cu(ОH)4] + Na2O2 = Cu2О3 + 6NaOH + H2O
Potassium superoxide being smelted with CuO gives potassium cuprate (III):
2KO2 + 2CuO = 2KCuO2 + O2
This crystalline substance is blue or deep blue. It is completely decomposed by water. Compounds of Cu(III) are unstable and behave as very strong oxidising agents:
2Cu2О3 + 4H2SO4 = 4CuSO4 + O2 + 4H2O.
Compounds of Ag
The initial compound to obtain practically any other compound of silver is AgNO3 that, in turn, is produced by dissolution of metallic silver in НNO3.
Compounds Ag(I). The brown precipitate of silver oxide is formed at the action of alkalis on solutions of Ag(I):
2AgNO3 + 2NаOН = Ag2O + Н2О + 2NаNO3
AgOH exists in very diluted solutions, otherwise it decomposes.
Ag2О is slightly soluble in water (~ 0,02 g/L at 20°). It reacts reversibly with water that is attended by the relatively strong base AgOH formation:
1/2Ag2О + 1/2Н2О AgОН Ag+ + ОН-
The values of equilibrium constants К1 and К2 are 1,8×10-6 і 2×10-2, respectively. Therefore, saturated solutions of Ag2O have a pH more than 7.
Ag2О has predominately basic properties. It reacts with strong acids:
Ag2О + 2HNO3 = 2AgNO3 + H2О,
though it can be dissolved in concentrated solutions of alkalis forming dihydroxoargentate anion:
Ag2О + H2О + 2NaOH Na[Ag(OH)2]
It can be decomposed at 160 oC:
2Ag2О
4Ag
+ О2
Salts. Soluble salts of Ag(I) with acid residues of strong acids don’t hydrolyse (AgNO3, AgClO4 etc.) since AgОН is a relatively strong base.
The solubility of silver halides is decreased in the series AgF to AgI. Insoluble halides AgCl (white), AgBr (yellowish), AgI (yellow) can be obtained by double replacement reactions:
AgNO3 + KCl = AgCl↓ + KNO3
SP in this series is also decreased gradually: AgCl 1,6×10-10, AgBr - 8×10-13, AgI -1,5×10-16.
Ammonia forms with Ag(I) the cationic complex [Ag(NH3)2]+. The dissolution of slightly soluble AgCl causes donor-acceptor interaction with NH3:
AgCl↓ + 2NH3 = [Ag(NH3)2]Cl
This reaction is reversible and the equilibrium is shifted to the formation of complex at the conditions of excess of ammonia. The equilibrium of the reaction in case of other halides is gradiually displaced to the reverse direction and AgI virtually inactive to NH3.
Complexes. Coordination compounds of Ag(I) (Tollens' reagent) with ammonia can be reduced by aldehydes, glucose or some other reducing agents. A “silver mirror” forms in a clean glass reaction vessel. This feature is used as a test for aldehydes, which are oxidized to carboxylic acids.
2[Ag(NH3)2]Cl + R-COH + H2O = 2Ag↓ + RCOOH + 2NH4Cl + 2NH3
This reaction is applied worldwide to produce mirrors and as a qualitative test on aldehydes.
The most stable complexes of Ag(I) are coordination compounds with thiosulfate anion. Therefore, all halides of silver are soluble in Na2S2O3:
AgBr + 2Na2S2O3 = Na3[Ag(S2O3)2] + NaBr
This reaction is used in black-and-white photography to remove AgBr after development (fixing solution). Ag(I) forms coordination compounds with alkynes and alkenes (for instance Ag-C≡C-Ag) alkyl and aryl derivatives of phosphines.
Compounds of Ag(II) and Ag(III). Many compounds of Ag(ІІ) are known but they are very unstable:
Ag + F2 = AgF2
Ag2O + (NH4)2S2O8 + H2O = 2AgO + (NH4)2SO4 + H2SO4
AgO is a very strong oxidant:
4AgO + 2H2SO4 = 2Ag2SO4 + O2 + 2H2O
Ag2O3. It can be obtained by the anode electrodeposition of Ag(І) in alkali solutions.
Fluorine can oxidize halides of silver and fluorocomplexes can be obtained:
KCl + AgCl + 2F2 = K[AgF4] + Cl2