Compounds of copper

Oxidation state +2

Compounds Cu(II). Oxidants usually oxidize copper to Cu⁺².

CuO can be obtained by the direct synthesis reaction between simple substances and also by thermal decomposition of many oxygencontaining compounds Cu(II):

(CuOH)₂CO₃ = 2CuO + H₂O + CO₂;

2Cu(NO₃)₂ = 2CuO + 4NO₂ + O₂.

CuO is a powder of black colour decomposed at t^о > 800°С:

4CuO = 2Cu₂O + O₂

It is reduced readily at 250°С by hydrogen or СО:

CuO + Н₂ = Cu + Н₂O

Basic properties of CuO are most noticeable. This oxide reacts with strong acids:

CuO + 2HCl = CuCl₂ + Н₂O

while it interacts also with alkalis when melting:

CuO + 2NaOH = Н₂O + Na₂CuO₂ (cuprates).

Solutions of Cu(ІІ) form blue precipitate of Cu(ОН)₂ with alkalis. Cu(ОН)₂ can be decomposed easily when heating:

Cu(ОН)₂ = CuО + Н₂О

Cu(ОН)₂ can react with concentrated solutions of alkalis. Deep-blue hydroxocuprates are formed:

Cu(ОН)₂ + 2NaOH = Na₂[Cu(ОН)₄]

Na₂[Cu(ОН)₄] loses water at 200°С and becomes transformed into oxocuprate Na₂CuО₂.

Aquaions Cu²⁺ exist as aquacomplexes [Cu(Н₂О)₆]²⁺ that are coloured blue.

The most practically important compound is copper sulfate that can be deposited with crystalline water CuSO₄×5H₂O (blue vitriol). It loses water after heating and nonaqueous CuSO₄ becomes colourless.

Some salts of copper (ІІ) are insoluble in water. The least soluble among them is black CuS that is formed at the action of H₂S or soluble sulfides on compounds of Cu(ІІ):

Сu²⁺ + H₂S = CuS + 2H⁺

Copper carbonate CuСО₃ has not been prepared up to the present. Insoluble basic salt appears at the action of carbonates on Cu(ІІ):

2СuSO₄ + 2Na₂СО₃ + H₂О = (CuОН)₂СО₃↓+ 2Na₂SO₄ + СО₂

Crystalline basic carbonates are encountered in nature in the form of beautiful green-coloured mineral malachite (CuОН)₂СО₃ (or Cu(ОН)₂CuCО₃) and deep blue azurite 2CuCО₃×Cu(ОН)₂.

Complexes. Formation of complexes is a quite typical behavior of Сu(ІІ). All coordination compounds are coloured since d-sublevel of Сu²⁺ is not completed (3d⁹). Coordination number can be varied: 4 (square planar) or 6 (octahedral).

Nonuniformity of ligands of Cu(II) complexes with coordination number 6 can be shown by the Crystal Field Theory (see scheme below). The least repulsion occurs if unpaired 3d-electron is situated at d_x²_-y²-orbital that is closest to 4 ligands with negative charge. The appearance of electron pair of d_z²-orbital initiates strong repulsion of ligands along z-axis. Therefore, complexes of Cu(II) frequently have space configuration of distorted octahedron. These complexes are shown sometimes in literature as follows: [Cu(H₂O)₄(H₂O)₂]²⁺, [Cu(OH)₄(OH)₂]^4-.

Water molecules of the inner sphere are substituted at the action of NH₃ on Cu(II). In this case [Cu(NH₃)₄(H₂O)₂]²⁺ forms of deep blue colour. Cu(NH₃)₄SO₄·H₂O compound can be prepared by adding concentrated ammonia solution, NH₃, to a saturated aqueous solution of copper sulfate, CuSO₄, until all the copper(II) hydroxide that is initially formed redissolves into a clear deep blue solution. The displacement of the fifth water molecule takes place in the concentrated ammonia only. It can be proved by stability constants of complexes (К₁=1,4×10⁴, К₂=3,2×10³, К₃=7,8×10², К₄=1,4×10² і К₅=0,3).

Дата добавления: 2015-07-25