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Complexes in which a metal is bonded to more than one kind of donor groups is called Heteroleptic complexes.

Ex- [CO(NH₃)₄ Cl₂]⁺ 

(ii), (iv)

(ii) [Fe(NH₃)₄ Cl₂]⁺  

(iv) [Co(NH₃)4Cl₂]

(i), (ii), (iii)

(i) It is a neutral ligand.
(ii) It is a didentate ligand.
(iii) It is a chelating ligand.

(i), (iii)

(i) [Co(en)₃]³⁺ 

^{(iii) cis– [Co(en)₂ Cl₂]+}

An optically active complex of the type [M(AA)₂X₂]ⁿ⁺ indicates cisoctahedral structure, e.g. cis-[Pt(en)₂Cl₂]²⁺ or cis-[Cr(en)₂Cl₂]⁺

1. No.

2. They are charged ligands.

3. If a polydentate ligand is coordinated to the metals, a ring structure is obtained. It is called chelate and the phenomenon is called chelation.

The equilibrium constant of the complex depends on the following factors :

(a) Charge to size ratio of the metal ion : 

Higher the ratio greater is the stability. For the divalent metal ion complexes their stability shows the trend : Cu²⁺ > Ni²⁺ > Co²⁺ > Fe²⁺ > Mn²⁺ > Cd²⁺. The above stability order is called the Irving-William order. In the above list both Cu and Cd have the charge + 2, however, the ionic radius of Cu²⁺ is 69 pm and that of Cd²⁺ is 97 pm. The charge to size ratio of Cu²⁺ is greater than that of Cd²⁺. Therefore the Cu²⁺ forms stable complexes than Cd²⁺.

(b) Nature of the ligand : 

A second factor that governs stability of the complexes is related to how easily the ligand can donate its lone pair of electrons to the central metal ion that is, the basicity of the ligand. The ligands those are stronger bases tend to form more stable complexes.

Since CI^- is a weak ligand, there is no pairing of electrons. 

Number of unpaired electrons = 2 

Type of hybridisation = sp³ 

Geometry of complex ion = Tetrahedral 

The complex ion is paramagnetic.

Cis/trans - diamminedicloridoplatinum (II)

[Co(NH₃)₄ (H₂O) Cl] (NO₃)_2.

Pentaamminesulphatocobalt (III) chloride.

[Pt(NH₃)₂ Cl(NO₂)]

Complex ion is eclectically charged species formed by co-ordination of a simple cation with a number of neutral or charged ligands. 

E.g hexacyanoferrate(III)

Formation of stable complex polydentate ligand due to stronger bonding is known as chelate effect.

[Co(en)₃]³⁺ : Because (en) is a chelating ligand /bidentate ligand.

In Lead poisoning EDTA (Ethylene diamine tetraacetate) is used as ligand which is hexadentate i.e., the denticity of EDTA is 6. EDTA binds with metal in octahedral manner by two N-atoms and four acetate oxygen atoms.

[CoCl₂(en)₂]⁺

K₃[Al(C₂O₄)₃]

(i) [Zn (O₄)]^2-
(ii) K₂ [Pd Cl₄]
(iii) [Pt (NH₃)₂ Cl₂]
(iv) K₂[Ni(CN)₄]
(v) [CO (NH₃)₅ (ONO)]²⁺
(vi) [CO (NH₃)₆]₂(SO₄)₃
(vii) K₃ [Cr (C₂O₄)₃]
(viii) [Pt (NH₃)₆]⁴⁺
(ix) [Cu (Br₄)^2-
(x) [CO (NO₂) (NH₃)₅]²⁺

(i) Hexaamminecobalt (III) chloride.
(ii) Diamine chlorido (methylamine) platinum (II) chloride.
(iii) Hexaaquatitanium (III) ion.
(iv) Tetraamminichloridonitrite – N – cobalt (HI) chloride.
(v) Flexaquamanganese (II) ion.
(vi) Tetrachloridononickeiate (II) ion.
(vii) Hexaammmenickei (11) chloride,.
(viii)Tris (ethane -1,2 - diammine) cobalt (III) ion.
(ix) Tetracarbonylnickel (O)

(i) Diamminechloridomethyleamineplatinum (ii) chloride 

(ii) Tetraaminechloridonitrito-N-cobalt (iii) chloride

The order of the ligand in the spectrochemical series is H₂O < NH₃ < NO₂^-. 

Hence the wavelength of the light observed will be in the order :

[Ni(H₂O)₆]²⁺ < [Ni(NH₃)₆]²⁺ < [Ni(NO₂)₆]^4-

Thus, the wavelength of light absorbed (E = \(\frac{hc}{\lambda}\) ) will be in the opposite order :

[Ni(H₂O)₆]²⁺ > [Ni(NH₃)₆]²⁺ > [Ni(NO₂)₆]^4-

The energy of d_xy, d_yz and d_xz orbitals (t_2g set) increases by 2/5Δ_t and that of d_x²-y² and d_z² orbitals (e_g set) decreases by 3/5 Δ_t .

If the crystal field splitting energy is greater than the pairing energy, the fourth electron will pair at the t_2g level and if the pairing energy is greater than the crystal field splitting energy the electron will go to the on e_g level.

A bidentate ligand like (en), can form two coordinate bonds with the metal at the same time.

An amidentate ligand like -NO₂ can form only one coordinate bond with the metal at a time. But it can ligate through two different atoms.

Tetraamminechloridonitrito-N-cobalt (III) chloride.

[CoCl₂(en)₂]Cl.

Option : (d) square planar and tetrahedral respectively

The ionisable groups written outside the square bracket. 

Ex- K⁺ in K₄[Fe(CN)₆] OR 3Cl^- in [Co(NH₃)₆]Cl₃

(1) In biology : Several biologically important natural compounds are metal complexes which play an important role in number of processes occurring in plants and animals.

For example, 

Chlorophyll in plants is a complex of Mg²⁺ ions, haemoglobin in blood is a complex of iron, vitamin B₁₂ is a complex of cobalt.

(2) In medicine : The complexes are used on a large scale in medicine. 

Many medicines in the complex form are more stable, more effective and can be assimilated easily.

For example,

Platinum complex [Pt(NH₃)₂CI₂] known as cisplatin is effectively used in cancer treatment. 

EDTA is used to treat poisoning by heavy metals like lead.

(3) To estimate hardness of water :

• The hardness of water is due to the presence Mg²⁺ and Ca²⁺ ion in water.
• The strong field ligand EDTA forms stable complexes with Mg²⁺ and Ca²⁺. 

Hence,

These ions can be removed by adding EDTA to hard water.

Similarly these ions can be selectively estimated due to the difference in their stability constants.

(4) Electroplating : This involves deposition of a metal on the other metal. For smooth plating, it is necessary to supply continuously the metal ions in small amounts.

For this purpose, 

A solution of a coordination compound is used which dissociates to a very less extent. 

For example, 

For uniform and thin plating of silver and gold, the complexes K[Ag(CN)₂] and K[Au(CN)₂] are used.

Option : (a) tetra carbonyl nickel (O)

Option : (a) [Ni(CN)₄]^2-

Coordination sphere : [Ni(NH₃)₆]²⁺ 

Counter ions : Cl^-

• A large number of coordination compounds show wide range of colours due to d – d transition of electron and this can be explained by crystal field theory (CFT).
• The complex absorbs the light in one visible region (400 nm to 700 nm) and transmits the light in different visible region giving complementary colour.
• Consider an octahedral purple coloured complex of [Ti(H₂O)₆]³⁺ which absorbs green light and transmits purple colour. Similarly [Cu(H₂O)₆]²⁺ absorbs the light in the red region of radiation spectrum and transmits in the blue region, hence the complex appears blue.
• The absorption of light arises due to d-d transition of electron from lower energy level (t_2g) to higher energy level (e_g) in octahedral complex.
• The energy required for transition depends upon crystal field splitting energy Δ₀. If Δ₀ = ΔE, then the energy of an absorbed photon (hv) is ΔE = hv = \(\frac{hc}{\lambda}\) where λ, v and c are wavelength, frequency and velocity of the absorbed light.
• Higher the magnitude of Δ₀ or ΔE, higher is the frequency or lower is the wavelength of the absorbed radiation.
• Since Δ₀ depends upon nature of metal atom or ion, its oxidation state, nature of ligands and the geometry of the complex, different coordination compounds have different colours. 

CuSO_4(aq) + 4KCN_(aq) → K₂Cu (CN)₄]_(aq) + K₂SO₄

i.e. [Cu (H₂O)₄]²⁺ + 4CN^- → [Cu(CN)₄]^2- + 4H₂O

Thus, the coordination entity formed in the process is K₂ [Cu (CN)₄]. K₂ [Cu (CN)₄] is a very stable complex which does not ionize to give Cu²⁺ ions when added to water. Hence Cu²⁺ ions are not precipitated when H₂S_(g) is passed through the solution.

Double salts are crystalline molecular or addition compounds containing more than one salt in simple molecular proportions soluble in water and in solution they ionise and exhibit all the properties of the constituent ions.

For example,

K₂SO₄ +Al₂(SO₄)₃ - 24H₂O

K₂SO₄ . Al₂(SO₄)₃ . 24H₂O_(aq) ⟶ 2K⁺_(aq) + 2Al³⁺_(aq) + 4SO^2-_4(aq) + 24H₂O

(i) Linkage isomerism

(ii) Optical isomerism

(ii) Cis- trans/ geometrical isomerism.

In the coordination compounds (complexes) the ligands are linked to the central metal atom or ion by coordinate bonds which are directional in nature and hence give rise to the phenomenon of stereoisomerism.

In this isomerism, 

The different stereoisomers have different arrangements of ligands (atoms, molecules or ions) in space around the central metal atom or ion. 

Hence,

They have different physical and chemical properties and give rise to the phenomenon of stereoisomerism.

1, 1, 1, 1 - Tetra Chloro methane.

The dipole moment decreases with increase of halogen atom except fluoromethane. 

(chloromethane > fluoromethane> bromomethane > iodomethane)

The C-X bond length increases with the increase of size of halogen atom and bond enthalpy decreases.

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(a) For the complex ion, [Zn(NH₃)₄]²⁺ : 

Atomic number of Zn = Z = 30 

Charge on metal ion = + 2

\(\therefore\) Number of electrons lost by Zn atom = X = 2 Total number of electrons donated by \(4NH^{2^3}\)

ligands = Y = 2 x 4 = 8 

EAN = Z – X + Y 

= 30 – 2 + 8 

= 36

(Note : This is atomic number of the nearest inert element 3₆Kr.)

(b) For the complex ion, [Fe(CN)J^4- : 

For Fe, Z = 26 (Atomic number) 

X = 2 (Due to + 2 charge on Fe) 

Y = 12 (Due to 6 CN^- ligands) 

∴ EAN = Z – X + Y 

= 26 – 2 + 12 

= 36

(i) [Co(CO₃)₃]^3- 

(ii) Na₃[Fe(CN)₆] 

(iii) K₄[Fe(CN)₆] 

(iv) Co(en)₂(H₂O)(Cl) 

(v) [Cr(H₂O)₄CI₂]CI 

(vi) Pt(NH₃)₂Cl₂

The ions or molecules bound to the central atom/ion in the coordination entity are called Ligands.

1. The IUPAC name of the coordination compounds :

• Diamminedichloridoplatinum(II)
• Potassium hexacyanoferrate(II)

 2. Type of isomerism

• [Cr(H₂O)₆]Cl₃ – Hydrate isomerism
• [CO(NH₃)₅ Br]SO₄ – Ionisation isomerism 
• [CO(NH₃)₅ NO₂]²⁺ – Linkage isomerism 
• [CO(NH₃)₆] [Cr(CN)₆] – Coordination isomerism.