Preparation and Applications of coordination compounds :

(1) Preparation: Coordination compounds are generally prepared by the application of the following methods,

(i) Ligand substitution reaction: A reaction involving the replacement of the ligands attached to the central metal ion in the complex by other ligands is called a ligand substitution reaction.

[Cu(H₂O)₄]²⁺_(aq) + 3NH_3(aq) → [Cu(NH₃)₄]²⁺_(aq) + 4H₂O(l)

^{Light blue                                                Deep blue}

(ii) Direct mixing of reagent:

PtCl₂ + 2H₂N – CH₂ – CH₂ – NH₂ → [Pt(en)₂Cl₂]
^{(en)                                                                   (Dichlorobis ethylene diam mine platinum) (II)}

(iii) Redox reactions: In these reactions, either oxidation or reduction is involved

2CO(NO₃)₂ + 8NH₃ + 2NH₄NO₃ + H₂O₂

2[CO(NH₃)NO₂](NO₃)₂ + 2H₂O
^{Pentaammine nitrocobalt (II) nitrate.}

Application

(1) Estimation of hardness in water, as Ca⁺⁺ and Mg²⁺ ions form complexes with EDTA.

(2) Animal and plant world e.g. chlorophyll is a complex of Mg²⁺ and haemoglobin is a complex of Fe²⁺ vitamin B₁₂ is a complex of Co²⁺.

(3) Electroplating of metals involves the use of complex salt as electrolytes e.g. K[Ag(CN)₂] in silver plating.

(4) Extraction of metals e.g. Ag and Au are extracted from ores by dissolving in NaCN to form complexes.

(5) Estimation and detection of metal ions e.g. Ni²⁺ ion is estimated using dimethyl glyoxime.

(6) Medicines e.g. cis-platin i.e. cis [PtCl₂(NH₃)₂] is used in treatment of cancer.