Tetraammine copper (II) sulphate.

Six

Tetrahedral complexes do not exhibit geometrical isomerism. Because the relative position of donor atoms of ligand the unidentate Iigands (donor atom) attached to the central atom are same with respect to each other.

Medicinal uses
(i) Ca-EDTA chelate, is used in the treatment of lead and radioactive poisoning.
(ii) That is for removing lead and radioactive metal ions from the body.
(iii) Cis-platin is used as an antitumor drug in cancer treatment.
Biological Importance compounds:-
(i) Fe²⁺ - porphyrin complex: It plays an important role in carrying oxygen from lungs to tissues and tissue carbon dioxide from to lungs.
(ii) Chlorophyll - useful in photosynthesis in plants.

(i) \(\mathrm{Mg}\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right) \mathrm{Cl}_{5}\right]^{2-} \rightleftharpoons \mathrm{Mg}^{2+}+\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right) \mathrm{Cl}_{5}\right]^{2-} (2 ions)\)
(ii) \(\begin{aligned} {\left[\mathrm{Cr}\left(\mathrm{NH}_3\right)_5 \mathrm{Cl}_3\left[\mathrm{CoF}_6\right]_2 \rightleftharpoons 3\right.} & {\left[\mathrm{Cr}\left(\mathrm{NH}_3\right)_5 \mathrm{Cl}\right]^{2+} } \\ & (5 \text { ions }) \end{aligned}\)\(+2\left[\mathrm{CoF}_6\right]^{3-}\)
(iii) \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{3} \mathrm{Cl}_{3}\right]= \text{ No ions}\)
If no of ions increases, molar conductivity increases molar conductivity of the complex also INCREASES.
\(\therefore\) The order of the given compound is
[Cr(NH₃)₃Cl₃]<Mg[Cr(NH₃)₃Cl₃] < [Cr(NH₃)₅Cl₃] [CoF₆]₂
  (No ion)          (2 ions)                    (5 ions)

Cisplatin is a square planar coordination complex (cis- [Pt (NH₃)₂Cl₂]), in which two similar ligands are in adjacent positions.

(i) The stability of a coordination complex is a measure of its resistance to the replacement of one ligand by another.
(ii) The stability of a complex refers to the degree of association between two species involved in an equilibrium.
(iii) Let us consider the following complex formation reaction
Cu²⁺ +4NH₃ ⇌ [Cu(NH₃)₄]^{2+
\(\beta =\frac { { \left[ { Cu\left( { NH }_{ 3 } \right) }_{ 4 } \right] }^{ 2+ } }{ \left[ { Cu }^{ 2+ } \right] { { \left[ { NH }_{ 3 } \right] }^{ 4 } } } \)}
(iv) So, as the concentration of [Cu (NH₃)₄]²⁺ increases the value of stability complexes also increases.
(v) Therefore the greater the value of stability constant greater is the stability of the complex.

(i) UNIDENTATE LIGAND: (or) Monodentate
When a ligand is bonded through one donor site to central metal atom/ion it is said to be unidentate ligand.
Eg: Cl^-, CO, NH³, H₂O, etc.
(ii) DIDENTATE LIGAND: (or) Bidentate
When a ligand is bonded through two donor sites to central metal atom/ion, it is said to be didentate ligand.
Eg: Oxalate, 1,2 - ethanediamine.
(iii) AMBIDENTATE LIGAND:
When a ligand i.s bonded through two different atoms, it is said to be ambidentate ligand.
Eg: NO₂-, SCN^-, CN^-

[Co (en)₂ Cl₂]⁺ This is an octahedral complex

(i) The ligand ➝ metal bond in a coordination complex is covalent in nature. It is formed by sharing of electrons (provided by the ligands) between the central metal atom and the ligand.
(ii) Each ligand should have at least one filled orbital containing a lone pair of electrons.
(iii) In order to accommodate the electron pairs donated by the ligands, the central metal ion present in a complex provides required number (coordination number) of vacant orbitals.
(iv) These vacant orbitals of central metal atom undergo hybridisation, the process of mixing of atomic orbitals of comparable energy to form equal number of new orbitals called hybridised orbitals with same energy.
(v) The vacant hybridised orbitals of the central metal ion, linearly overlap with filled orbitals of the ligands to form coordinate covalent sigma bonds between the metal and the ligand.
(vi) The hybridised orbitals are directional and their orientation in space gives a definite geometry to the complex ion.
(vii) In the octahedral complexes, if the (n-1) d orbitals are involved in hybridisation, then they are called inner orbital complexes or low spin complexes or spin paired complexes. If the nd orbitals are involved in hybridisation, then such complexes are called outer orbital or high spin or spin free complexes. Here n represents the principle quantum number of the outermost shell.
(viii) The complexes containing a central metal atom with unpaired electron(s) are paramagnetic. If all the electrons are paired, then the complexes will be diamagnetic.
(ix) Ligands such as CO, CN^·, en, and NH₃ present in the complexes cause pairing of electrons present in the central metal atom. Such ligands are called strong field ligands.
(x) Greater the overlapping between the ligand orbitals and the hybridised metal orbital, greater is the bond strength.

(i) [NiCI₄]^2-
IUPAC name - Tetrachloridonickelate (II) ion
(ii) Ni²⁺ = 3d⁸,4s⁰

Cl^- being a weak field ligand cannot pair up the unpaired electron. So, it is sp³ hybridised, and it has tetrahedral geometry.

(i) It does not explain the colour of the complex.
(ii) It considers only the spin only magnetic moments and does not consider the other components of magnetic moments.
(iii) It does not provide a quantitative explanation as to why certain complexes are inner orbital complexes and the others are outer orbital complexes for the same metal. For example, [Fe(CN)₆]^4- is diamagnetic (low spin) whereas [FeF₆]^4- is paramagnetic (high spin).

[Ni (H₂O)₆]²⁺

It has two unpaired electrons. So there is d-d transition. Hence it is green coloured.
[Ni(CN)₄]^2-

There is no unpaired electrons. So it is colourless, as there is no d-d transition.

Most of the elements exhibit, two types of valence namely primary valence and secondary valence and each element tend to satisfy both the valences.
The primary valence is referred the oxidation state of the metal atom.
The secondary valence as the coordination number. For example, according to Werner, the primary and secondary valences of cobalt are 3 and 6 respectively.
The primary valence of a metal ions ae always satisfied by negative ions.
For example in the complex CoCI₃.6NH₃. The primary valence of Co is +3 and is satisfied by 3CI^- ions.
The secondary valence is satisfied by negative ions, neutral molecules, positive ions or the combination of these.
For example, in CoCl₃.6NH₃ complex primary valence of cobalt +3 and it is satisfied by 3 CI^-.
The secondary valence of cobalt is 6 and is satisfied by six neutral ammonia molecules. where as in CoCI₆.NH₃. 
Secondary valence of Co = 5{It is satisfied five neutral molecules and a Cl^- ion}
According to Werner, there are two spheres of attraction around a metal atom/ion in a complex.

The inner /coordination sphere:
The groups present in this sphere are firmly attached to the metal.
The outer sphere / ionisation sphere:
The groups present in this sphere are loosely bound to the central metal ion and hence can be separated into ions upon dissolving the complex in a suitable solvent.
The primary valencies are non-directional. while the secondary valencies are directional.
The geometry of the complex is determined by the special arrangement of the groups which satisfy the secondary valence.

Three isomers. If we consider any one of the ligands as reference (say Py), the arrangement of other three ligands (NH₃, Br^- and Cl^-) with respect to (Py) gives three geometrical isomers.

In all the complexes, the central metal ion is Co³⁺, among the given ligands CN^- is the strongest ligand, which causes large crystal
field splitting i.e maximum Δ₀

Ti⁴⁺ (d⁰ ⇒  0BM)
Co²⁺ (d⁷ spain free ⇒  t_2g⁵, e²_g; n = 3; μ = 3.9BM)
Cu²⁺  (d⁹ Low spain ⇒  t_2g⁶, e³_g; n = 1; μ = 1.732BM)
Ni²⁺  (d⁸ Low spain ⇒  t_2g⁶, e²_g; n = 2; μ = 2.44 BM)

The complex is [M(H₂O)₅Cl]Cl₂
1000 ml of 1 M solution of the complex gives 2 moles of Cl^- ions 1000 ml of 0.01 M solution of the complex will give 
\(\frac{100 ml \times 0.01M \times 2Cl^-}{1000 ml \times 1M}\)
= 0.002 moles of Cl^- ions