As metal ion is fixed, the increasing field strengths (CFSE values) of the ligands from the spectrochemical series are in the order: H₂O < NH₃ < NO₂
Thus, the energies absorbed for excitation will be in the order:
[Ni(H₂O)₆]²⁺<[Ni(NH₃)₆]²⁺<  [Ni(NO₂)₆]^4-
As \(E=\frac { hc }{ \lambda } \) the wavelengths absorbed will be in the opposite order.

The decreasing order of basic strength of the given amines and ammonia follows the following order:
(C₂H₅)NH > C₂H₅NH₂ > NH₃ > C₆H₅NH₂

(i) Primary
(ii) Tertiary
(iii) Primary
(iv) Secondary

(a) Biological processes: Chlorophyll contains Mg, which is used in photosynthesis. Haemoglobin contains Fe, which acts as oxygen carrier. Vitamin-B₁₂ contain cobalt which is used to preven anaemia.
(b) Analytical chemistry:
(i) Ni²⁺ is detected by using DMG (dimethylglyoxime)
(ii) EDTA is used for sofening of hard water.
(c) Medicinal chemistry: cis-Platin is used as anticancer agent.
(d) Metallurgical operation: Cyanide complexes are used in extraction of Ag and Au.

Add BaCI₂ solution. [Co(NH ₃)₅CI]SO₄ will give white precipitate due to formation of BaSO₄ whereas [Co(NH₃)₅SO₄]CI will not react. Add AgNO₃ solution. [Co(NH₃)₅SO₄]CI will give white precipitate due to formation of AgCl whereas [Co(NH₃)₅CI]SO ₄ will not react. It shows that these isomers produce different ions in aqueous solution, but have same chemical formula, therefore, they are ionisation isomers.

In each complex, Fe is in + 3 state , as C₂O^-₄is didentate chelating ligand. which forms chelate rings and hence. it is the most stable complex.

(i) Formation of M←C sigma bond through donation of lone pair of electrons of carbon (of CO) into empty orbital of metal atom. This is dative overlap.
(ii) Formation of M→Cπ bond through donation of electrons from filled metal d-orbitals into vacant antibonding π∗ molecular orbitals of CO.
 It is back donation or back bonding. It creates a synergic effect and strengthens the bond between CO and the metal.

A molecule or an ion which has only one donor atom to form one coordinate bond with the central metal atom is called unidentate ligand, e.g.Cl^- and NH₃.
A molecule or an ion which contains two donor atoms and hence forms two coordinate bonds with the central metal atom is called a didentate ligand, e.g.,
 \(\overset { { CH }_{ 2 }{ NH }_{ 2 } }{ \underset { { CH }_{ 2 }{ NH }_{ 2 } }{ | } } and\quad \overset { { COO }^{ - } }{ \underset { { COO }^{ - } }{ | } } \)
a molecule or an ion which contains two donor atoms but only one of them forms a coordinate bond at a time with the central metal atom is called ambidentate ligand, e.g. CN^- or NC^-and: NO^-₂ or ONO^-

Hinsberg's test is used for the identification of primary, secondary, and tertiary amines.
Hinsberg's reagent is benzenesulphonyl chloride (C_6​H₅​SO_2​Cl).
It reacts differently with primary, secondary, and tertiary amines.
(i) Hinsberg's reagent reacts with primary amines to form N− alkylbenzenesulphonyl amide which is acidic in nature and soluble in alkali.
Note: N− alkylbenzenesulphonyl amide contains a strong electron-withdrawing sulphonyl group. Due to this, the H− atom attached to nitrogen can be removed easily. Hence, it is acidic.
(ii) Hinsberg's reagent reacts with secondary amines to form a sulphonamide which is insoluble in alkali.
Note: As there is no hydrogen atom attached to the N atom in the sulphonamide, it is not acidic and insoluble in alkali.
(iii) Hinsberg's reagent does not react with tertiary amines.

(i) Gabriel phthalimide synthesis: This reaction is used for the preparation of aliphatic primary amines. In this reaction, phthalimide is first of all treated with ethanolic KOH to form potassium phthalimide. Potassium phthalimide on treatment with alkyl halide gives N-alkyl phthalimide, which on hydrolysis with dilute hydrochloric acid gives a primary amine as the product.

(ii) Coupling reactions: Diazonium salts react with aromatic amines in weakly acidic medium and phenols in weakly alkaline medium to form coloured compounds called azo dyes by coupling at p-position of amines or phenol. The mechanism is basically that of electrophilic aromatic substitutions where the diazonium ion is electrophile.

(iii) Hoffman’s bromamide reaction: When a primary acid amide is heated with an aqueous or ethanolic solution of NaOH or KOH and bromine (i.e., NaOBr or KOBr), it gives a primary amine with one carbon atom less.

Let us assume that the six ligands are positioned symmetrically along the cartesian axes, with metal atom at the origin. As the ligands approach, first there is an increase in energy of d-orbitals relative to that of the free ion just as would be the case in a spherical field  The orbitals lying along the axes (\({ d }_{ { z }^{ 2 } }\)nd \({ d }_{ { x }^{ 2 }-{ y }^{ 2 } }\))get repelled more strongly than dx¹ d and d_yz and d_zx orbitals which have lobes directed between the axes. The \({ d }_{ { z }^{ 2 } }\)and  orbitals get raised in energy and d_xy d_yz d _xz orbitals are lowered in energy relative to the average energy in the spherical crystal field. Thus, the degenerate set of d-orbitals get split into two sets : the lower energy orbitals set and the higher energy orbitals eg set. The energy is separated by t_2g and the higher energy orbitals e_g set. The energy is separated by \({ \Delta }_{ 0 }\)

(a) [Cr(C₂O₄)₃]^3-

(b) [PtCl₂(en)₂]²⁺
 
(c) [Cr(NH₃)₂Cl₂(en)]⁺

Carbylamine reaction yields isocyanides.

Benzylamine is most basic

(i) Ionisation isomerism:
Those isomers which produce different ions in aqueous solution are called ionization isomers. In ionization isomers counter ions are ligands which can replace ligands,
e.g. [Co(NH₃)₅SO₄Br and [Co(NH₃)₅Br]SO₄
(ii) Linkage isomers:
Those isomers which have ambidentate ligands can show linkage isomerism. They differ in donor atom forming coordinate bond,
e.g. [Co(NH₃) ₅ NO₂]²⁺ and [Co(NH₃) ₅ONO]²⁺.
(iii) Coordination isomerism:
It arises from the interchange of ligands between cationic and anionic entities of different metal ions present in a complex,
e.g. [Co(NH₃)₆ ]₆Cr(CN)₆] and [Cr(NH3)₆][Co(CN)₆]
(iv) Solvate isomerism:
They differ in number of solvent molecules forming coordinate bond with central metal ion,
e.g. [Cr(H₂O)₅]CI₃ is violet; whereas [Cr(H₂ O)₅CI]CI₂.H₂ O is greyish green.

(a) (i) Hofmann Bromamide Degradation Reaction This reaction is used for preparing amine contaning one carbon less than the starting amide. This method was developed for the preparation of primary amines by reacting an amide with Br₂/ Cl₂ in NaOH/KOH.
In this reaction, migration of an alkyl or aryl group takes place from carbonyl carbon of the amide to the N-atom.

\(\begin{equation} R-\mathrm{NH}_{2}+\mathrm{Na}_{2} \mathrm{CO}_{3}+2 \mathrm{NaBr}+2 \mathrm{H}_{2} \mathrm{O} \end{equation}\)
\(\begin{equation} \text { e.g. } \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CONH}_{2}+\mathrm{Br}_{2}+4 \mathrm{NaOH}\\ \text { Amide } \end{equation}\)⟶\(\begin{equation} \begin{aligned} &3 \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}+\mathrm{Na}_{2} \mathrm{CO}_{3}+2 \mathrm{NaBr}+2 \mathrm{H}_{2} \mathrm{O}\\ &\text { Amine } \end{aligned} \end{equation}\)
(ii) Diazotisation The conversion of primary aromatic amines into their diazonium salts is called diazotisation. Benzene diazonium chloride is prepared by the reaction of aniline with nitrous acid (which is produced by the reaction of NaNO₂ and HCI) at 273-278K or 0-5^oC as shown below:
\(\begin{array}{r} \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}+\mathrm{NaNO}_{2}+2 \mathrm{HCl} \stackrel{273-278 \mathrm{~K}}{\longrightarrow} \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~N^+}_{2}{\mathrm{Cl^-}}+ \mathrm{NaCl}+2 \mathrm{H}_{2} \mathrm{O} \end{array}\)
Due to its unstability, the diazonium salt is not generally stored and is used immediately after its preparation. 
(iii) Gabriel Phthalimide Synthesis When a phthalimide is treated with ethanolic KOH, it forms potassium salt of phthalimide which on heating with alkyl halide followed by alkaline hydrolysis forms corresponding primary amines as shown below.

Primary amines are produce through this method without the traces of secondary or tertiary amines. So, this method is preferred for the synthesis of primary amines.

 

(b) C₂H₅NH₂ < (C₂H₅)₃N < (C₂H₅)₂NH
(c) Add CHCl₃ and alc. KOH, C₆H₅-NH₂ gives foul smell of isocyanide whereas C₆H₅-NH-CH₃ does not (or any other correct test).

(i) [Ni(CN)₄]^2-
Ni is in the +2 oxidation state i.e., in d⁸ configuration.
There are 4 CN⁻ ions. Thus, it can either have a tetrahedral geometry or square planar geometry. Since CN⁻ ion is a strong field ligand, it causes the pairing of unpaired 3d electrons.

CN^– will cause pairing of electrons. It is diamagnetic in nature due to the unpaired electron. 
(ii) [Ni(Cl₄)]2–
In case of [NiCl4] ²⁻, Cl⁻ ion is a weak field ligand. Therefore, it does not lead to the pairing of unpaired 3d electrons. Therefore, it undergoes sp3 hybridization. Since there are 2 unpaired electrons in this case, it is paramagnetic in nature.

(c) Aromatic primary amines cannot be prepared by the Gabriel phthalimide synthesis because aryl halides do not undergo nucleophilic substitution reaction with the anion formed by phthalimide. Thus, (A) is correct but (R) is incorrect

(b) Ethane-1, 2-diamine is a neutral ligand as it carries no charge. Oxidation number of Co in the complex ion is +3. Both (A) and (R) are correct but (R) is not the correct explanation of (A).

(i) (c): Spectrochemical series:
\((\mathrm{I}^{-}<\mathrm{Br}^{-}<\mathrm{SCN}^{-}<\mathrm{Cl}^{-}<\mathrm{S}^{2-}<\mathrm{F}^{-}<\mathrm{OH}^{-}<\mathrm{C}_{2} \mathrm{O}_{4}^{2-}<\mathrm{O}^{2-}< \mathrm{H}_{2} \mathrm{O}<\mathrm{NCS}^{-}<\mathrm{EDTA}^{4-}<\mathrm{NH}_{3}\)(ii) (b)
(iii) (a) : When Δ_o > P, the electrons paired up in the t_2g level rather than going to the e_g level, so
when Δ_o> P : \(t_{2 g}^{4} e_{g}^{0}\)
and Δ_o < P : \(t_{2 g}^{3} e_{g}^{1}\)
(iv) (d): Fe²⁺: 3d⁶ ⇒\(t_{2 g}^{4} e_{g}^{2}\)
(Since, F^- is a weak field ligand)
Hence four unpaired electrons are present.
Magnetic moment (μ)\(=\sqrt{n(n+2)}=\sqrt{4(4+2)}=4.9 \mathrm{~B} \cdot \mathrm{M}\)

(i) (d): It involves sp³ d² hybridisation and not d²sp³.
(ii) (d) : [Co(NH3)₆]³⁺ is d²sp³ hybridised with all electrons paired hence, it is diamagnetic and inner
orbital complex.

(iv) (c): Inner orbital complexes are formed with strong ligands as they force electrons to pair up and hence the complex will be either diamagnetic or will have less number of unpaired electrons.