Coordination Compounds

Optical isomers are the one which rotate the plane polarized light by a certain angle when passed through them and are mirror images of each other, also called as stereoisomer.

(i) C₂O₄ ^2- is a bidentate ligand so it can attach to central atom at two sites, forming a chelate ring. In the complexes of this type, three symmetrical bidentate chelating ligands AA are coordinated to the central metal atom M. Such complexes do not possess any element of symmetry and are optically active. Moreover, these complexes can be resolved into optical

(ii) In this complex Cl is an unidentate ligand with one site of attachment whereas -en (ethylenediamine) is bidentate ligand with two sites of attachment. The complexes in which two symmetrical bidentate chelating ligands AA and two monodentate ligands a, are coordinated to central metal atom M, exhibit the phenomenon of optical isomerism and can be resolved into their optical

An example of this type of complexes is given as shows both geometrical as well as optical isomerism. Its cis form is unsymmetrical, while the trans form is symmetrical because it contains a plane of symmetry. Hence, optical isomerism is shown by cis form.

(iii) In this there are three types of ligands. One is ammonia which is neutral (nitrogen donates the lone pair of electron to metal), Cl ^- ligand is unidentate and -en is bidentate ligand. Coordination number is 6. Two optical isomers are possible due to presence of 3 types of

Isomers are the compounds which have same chemical formula but different arrangement of atoms in space. There are principle two types of isomerism:

(i) Stereo isomerism

(ii) Geometrical isomerism

(iii) Optical isomerism

(iv) Structural isomerism

(v) Ionisation isomerism

(vi) Linkage isomerism

(vii) Coordination isomerism

(viii) Solvate isomerism

Geometrical isomerism comes into existence by the different spatial arrangement of groups around the central metal atom. Similar groups may either be arranged on the same side or on opposite sides of the central metal atom. This gives rise to two types of isomers called cis and trans isomers. When groups under consideration are arranged on the same side of the central metal atom, isomers are called cis isomers and when the groups under consideration are spatially placed on the opposite sides, isomers are called trans isomer.

(i) Starting with cation, the complex ion contains six ammonia molecules with cobalt in + 3 oxidation The name of compound: [Co (NH₃)₆]Cl₃ is hexaamminecobalt (III) chloride.

(ii) The complex ion is cation, so there are 2 ammonia molecules, one chloride ion and methyammine molecule qith platinum in + 2 state. Going in alphabetical order, the name of compound: [Pt (NH₃)₂Cl (NH₂CH₃)]Cl is diamminechloridomethylammineplatinum (II)

(iii) It is a complex cation with six water molecules and titanium atom in + 3 state. The name of the compound: [Ti (H₂O)₆]³⁺ is hexaaquatitanium (III) ion

(iv) The complex ion is cation with cobalt in + 3 state and with four ammonia molecules etetraammine, one chloride ion and nitrate ion. The name of the compound: [Co (NH₃)₄Cl (NO₂)]Cl is tetraamminechloridonitritocobalt (III) chloride.

(v) The complex ion is cation with manganese in + 2 state and six water The name of compound: [Mn (H₂O)₆]²⁺ is hexaaquamanganese (II) ion.

(vi) The complex is anion with nickel in + 2 state and with four chloride ions. The name of the compound: [NiCl₄]^2– is tetrachloridonickeltate (II)

(vii) The complex is cation with nickel in + 2 state and six ammonia molecules. The name of compound: [Ni (NH₃)₆]Cl₂ is hexaamminenickel (II) chloride.

(viii) The complex is cationwithcobalt in + 3 stateand there is a bidentate ligand called as The name of compound : [Co (en)₃]³⁺ is tris (ethylenediamine)cobalt (III) ion.

(ix) It is neutral complex with four carbonyl molecules and cobalt in 0 state. The name of compound: [Ni (CO)₄] is tetracarbonylcobalt (0).

(i) Tetrahydroxidozincate (II) = [Zn (OH)₄]^-2

Tetrahydroxi means 4 hydroxide ions with zinc in + 2 oxidation state. Hydroxide ions have a negative charge of -1, so balancing the overall charge of the coordination compound to be zero we get the formula as : [Zn (OH)₄]^-2

(ii) Potassium tetrachloridopalladate (II) = K₃ [PdCl₄].

Tetrachlorido means 3 Chloride ions each having a negative charge. Platinum is in + 2 state. Balance overall charge as 0, no. Of potassium ions are 3. Formula: K₃ [PdCl₄].

(iii) Diamminedichloridoplatinum (II) = [Pt (NH₃)Cl₂]²⁺

Diammine means 2 ammonia molecules, dichlorido means 2 chloride ions, platinum in + 2 state. Formula: [Pt (NH₃)Cl₂]²⁺

(iv) Potassium tetracyanidonickelate (II) = K₂ [Ni (CN)₄].

tetracyanido means 4 cyanide ions each with a unit negative charge and nickel atom with + 2 state. Formula: K₂ [Ni (CN)₄].

(v) Pentaamminenitrito-O-cobalt (III) = [Co (ONO) (NH₃)₅]⁺²

penataammine means 5 ammonia molecules, nitrito-O means nitrate ion which is bonded to central atom via oxygen and cobalt in + 3 state. Formula: [Co (ONO) (NH₃)₅]⁺²

(vi) Hexaamminecobalt (III) sulphate = [Co (NH₃)₆]₂ (SO₄)₃

Hexaammine means six ammonia molecules and cobalt in + 3 state. Sulphate have a negative charge of-2 Balance overall charge as 0. Formula: [Co (NH₃)₆]₂ (SO₄)₃

(vii) Potassium tri (oxalato)chromate (III) = K₃ [Cr (C₂O₄)₃].

trioxolato means 3 oxolate ions and chromium in + 3 state. Balance overall charge as 0. Formula: K₃ [Cr (C₂O₄)₃].

(viii) Hexaammineplatinum (IV) = [Pt (NH₃)₆]⁴⁺

hexaammine means 6 neutral ammonia molecules and platinum in + 4 state. Balance overall charge as 0. Formula: [Pt (NH₃)₆]⁴⁺

(ix) Tetrabromidocuprate (II) = [Cu (Br)₄]^2-

tetrabromido means 4 bromide ions with a unit negative charge each and copper in + 2 state. Balance overall charge as 0. Formula: [Cu (Br)₄]^2-

(x) Pentaamminenitrito-N-cobalt (III) = [Co (NO₂) (NH₃)₅]²⁺

pentaammine means 5 neutral ammonia molecules, nitrito-N means nitro group bonded to central atom via the lone pair of electron of nitrogen and cobalt in + 3 state. Balance overall charge as 0. Formula: [Co (NO₂) (NH₃)₅]²⁺

(i) Let Oxidation of Co be x and charge on the complex is given as + 2

H₂O has Oxidation Number: 0

CN has Oxidation Number: -1

en has Oxidation Number :0

 

(ii) Let Oxidation number of Co be x and charge on the complex is given as + 1

Br has Oxidation number: 1

en has oxidation number : 0

 

(iii) Let Oxidation number of Pt be x and charge on the complex is given as -2

Cl has oxidation number : -1

 

(iv) This complex can also be seen as [Fe (CN)₆]^3-

Let Oxidation number of Fe be x and charge given on the complex is given as -3

CN has oxidation number : -1

(v) Let Oxidation number of Cr be x and charge given on the complex is given as 0

NH₃ has oxidation number : 0

Cl has oxidation number: -1

Ligands are the neutral or negatively charged entities surrounding the central metal atom of the coordination complex which possesses at least one unshared pair of electrons.

Based on the number of donor sites of these ligands, Ligands are classified as:

Unidentate ligands: These Ligands which have only one donor site are called unidentate ligands.

Example: F^-, Cl ^– etc.

Didentate ligands: These Ligands which have only two donor site are called didentate ligands.

Example: Ethane-1,2-diamine, Oxalate ion etc.

Ambidentate ligands: These ligands which can attach them with the central metal atom by two different atoms are called as ambidentate ligands.

(1) Coordination Entity: Coordination entity is a charged entity having positive or negative charge in which the central atom is surrounded by molecules which may be neutral/negatively charged called Ligands

Examples:

i. Cationic Complexes: [Cu (H₂O)₆]²⁺, [Al (H₂O)₆]³⁺

ii. Anionic Complexes: [CuCl₄]^2-, [Al (H₂O)₂ (OH)₄]^-

iii. Neutral Complexes: [Co (NH₃)₄ Cl₂], [Ni (CO)₄]

(2) Ligands: Ligands are the neutral or negatively charged entities surrounding the central metal atom of the coordination complex which possesses at least one unshared pair of electrons

Example: F^-, Cl^-, Br^-, I^-, H₂0, and NH₃

(3) Coordination Number: Coordination Number which is also called as Ligancy is the total number of ligands that are attached to the central metal atom of the coordination

Example: [Cr (NH₃)₂Cl₂Br₂]^? has Cr³⁺ as its central cation, and has a coordination number of 6

Al³⁺ has coordination number 4 in [AlCl₄]^- but 6 in [AlF₆]^3-.

(4) Coordination polyhedron: Coordination polyhedron is defined as the spatial arrangement of the ligands around the central atom of a coordination

Example:

In the figure: The pink Sphere depicts the central atom of the coordination entity.

(5) Homoleptic complexes: Complexes in which the central metal atom is surrounded only by the same kind of donor groups which are the ligands.

Example: [Ag (CN)₂]^-, [Fe (CN₆)]⁴⁺ etc.

(6) Heteroleptic complexes: Complexes in which the central metal atom is surrounded by more than one kind of donor groups which are the ligands.

Example: [Co (NH₃)₄ Cl₂] ⁺, [Co (NH₃)₅ Cl]²⁺