Coordination chemistry- Molecular or Addition Compounds,Double salt or lattice compound

 

Coordination chemistry

    ·      Is branch of inorganic chemistry dealing with the study of coordination compounds.

    ·    Coordination compound are the compounds in which the central atom is linked to a number of ions or neutral molecules by coordination bonds(this type of bond is formed between electron pair acceptor species and electron donor species)

    ·      These compounds play a vital role in our lives. Haemoglobin of blood and chlorophyll of plants, vitamin B-12 are also coordination compounds of Fe, Mg, Co respectively.

Molecular or Addition Compounds

·      When two or more simple salts are chemically combined together in definite of fixed  proportion by weight. the compounds formed are called molecular or addition compound.

Example K₂SO₄ +Al₂(SO₄)₃ + 24H₂O ------>  K₂S0₄·AI₂(SO₄)₃ ·24H₂O

                                                                                Alum

4KCN + Fe (CN)₂ ------ > Fe (CN)₂·4KCN

molecular or addition compound may be further classified into two types on  their behavior in an aqueous solution

a).Double salt or lattice compound

The addition compounds which are stable in solid state only but are broken down into individual constituents when dissolved in water (i.e. in aqueous, these are not stable)are called double salts or lattice compounds are called double salts.

KCl.MgCl₂ .6H₂O -------> K⁺ + 2Cl^-     + Mg²⁺ + 6H₂O

Example -

K₂SO₄. Al₂(SO₄ )₃ .24H2O— Potash Alum

FeSO₄(NH₄) ₂ SO₄ .6H2O— Mohr's salt

KCl.MgCl₂ .6H2O —Carnallite

b). Coordination or complex compounds   

Those molecular or addition compounds which retain their identity in aq. solution are called complex salt or coordination compound.

CuS0₄·4NH₃ -------->     [Cu (NH₃)₄]²⁺ + SO₄^2-

in other words, a coordination or complex compound may be defined. as a. molecular compound that results from the combination of two or more simple stable molecular compounds and retains its identity in the solid as well as in dissolved state.

Note- but the constituents in complex looses their identity in solid as well as in aqueous.

A complex ion may be defined as an electrically charged radical which consists of a central metal atom or ion surrounded by a group of ions or neutral molecules or both.

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