(i) Complex with co-ordination number 8 - Cu₂ [ZrF₈].
(ii) Complex with co-ordination number 7 - (NH₄)₃[ZrF₇].

Diammine silver (I) Chloride.

Six

(i) Oxidation state of the central metal ion : +2 (i.e) Mn²⁺
(ii) Co-ordination number : 6
(iii) Nature of ligand: CN^- (Negative ligand)
(iv) Magnetic property: Paramagnetic nature
(v) Electronic configuration: 

(vi) Oxidation state: +2 (or) Mn²⁺ of central metal ion

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.

(i) This is also called as salt isomerism.
(ii) This type of isomers arises when an ambidentate ligand is bonded to the central metal atom/ion through either of its two different donor atoms. In the below mentioned examples, the nitrite ion is bound to the central metal ion Co³⁺ through a nitrogen atom in one complex and through oxygen atom in other complex.
\(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{NO}_{2}\right)\right]^{2+}\)

Addition of an alcoholic solution of dimethylglyoxime to an ammoniacal solution of Ni(II) gives rose - red precipitate Ni[ONCC N OH]₂ Nickel Cis (dimethylglyoximate)

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

(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

Metal carbonyls are classified in two different ways as described below Classification based on the number of metal atoms present.
a. Mononuclear carbonyls
These compounds contain only one metal atom. For example, [Ni(CO)₄] - nickel tetracarbonyl is tetrahedral, [Fe(CO)₅] - Iron pentacarbonyl is trigonal bipyramidal, and [Cr(CO)₆] - Chromium hexacarbonyl is octahedral.
b. Polynuclear carbonyls
Metallic carbonyls containing two or more metal atoms are called polynuclear carbonyls. Polynuclear metal carbonyls may be Homonuclear [Co₂(CO)₈], [Mn₂(CO)₁₀], [Fe₃ (CO)₁₂] or heteronuclear [MnCo(CO)₉], [MnRe(CO)₁₀] etc.

(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.

In \(\left[\mathrm{Co}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]^{3-}\) Cobalt is in +3 oxidation state
\(\mathrm{Co}=[\mathrm{Ar}] 3 \mathrm{~d}^{7} 4 \mathrm{~s}^{2}  \)
\(\mathrm{Co}^{3+}=3 \mathrm{~d}^{6} 4 \mathrm{~s}^{\circ}\)

It is diamagnetic; n = 0
d²sp³ hybridisation; μ_s = 0

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.

(a) coordination isomers
(b) no isomerism ( different molecular formula)
(c)⬅NCS; ⬅SCN coordinating atom differs : linkage isomers

 The electronic configuration t_2g³, e²_g
[ 3 x (-0.4)+ 2(0.6)]Δ₀
[-1.2 + 1.2] Δ₀ = 0