What are the two types of valences in Werner’s theory of coordination compounds?

• Primary valence: These correspond to the oxidation state of the metal and are ionizable. They are satisfied by anions like Cl⁻ in CoCl₃.
• Secondary valence: These correspond to the coordination number of the metal and are non-ionizable. They are satisfied by ligands like NH₃.

How did Werner explain the different chloride precipitations in cobalt-ammonia complexes?

Werner found that in compounds like CoCl₃•6NH₃, some chloride ions could be precipitated with AgNO₃, while others remained in solution. He explained this by proposing secondary valences, which hold ligands and some anions in fixed positions around the metal. These anions do not ionize in solution, leading to different numbers of precipitable chloride ions.

What is a coordination entity?

A coordination entity consists of a central metal ion or atom surrounded by ligands in a fixed arrangement. It remains as a single unit in solution.

Example: In [Co(NH₃)₆]³⁺, cobalt (CO³⁺) is the central ion, and six ammonia (NH₃) molecules act as ligands.

What is a ligand?

A ligand is an ion or molecule that donates a pair of electrons to form a coordinate bond with a central metal ion.

Examples:

• Unidentate ligands (bind through one donor atom): Cl⁻, H₂O, NH₃
• Didentate ligands (bind through two donor atoms): C₂O₄^2- (oxalate), ethylenediamine (en)
• Polydentate ligands (bind through multiple donor atoms): EDTA^4- 

Define coordination number and give an example.

The coordination number is the number of ligand donor atoms directly bonded to the central metal ion.

Example: In [Cr(NH₃)₆]³⁺, the coordination number of Cr³⁺ is 6 because six NH₃ molecules are attached.

What is a coordination sphere?

The coordination sphere includes the metal ion and its directly attached ligands, enclosed in square brackets. The ions outside the brackets are counter ions.

Example: In K₄[Fe(CN)₆], the coordination sphere is [Fe(CN)₆]^4- and the counter ion is K⁺.

What is the difference between homoleptic and heteroleptic complexes?

• Homoleptic Complex: The metal ion is bonded to only one type of ligand. Example: [Co(NH₃)₆]³⁺.
• Heteroleptic Complex: The metal ion is bonded to two or more different ligands. Example: [Co(NH₃)₄Cl₂]⁺.

Name the coordination compound: [Cr(NH₃)₃(H₂O)₃]Cl₃.

Triamminetriaquachromium(III) chloride.

• NH₃ → ammine
• H₂O → aqua
• Cr³⁺ oxidation state indicated as (III)
• Cl₃ is outside the coordination sphere, so it's a counter ion.

Write the formula for potassium trioxalatoaluminate(III).

K₃[Al(C₂O₄)₃].

• Al³⁺ is central metal ion
• C₂O₄^2- (oxalate) is a bidentate ligand
• Since Al³⁺ has a +3 charge and oxalate contributes -6, three K⁺ ions balance the charge.

What are the types of isomerism in coordination compounds?

Give an example of geometrical isomerism.

• Cis-[Pt(NH₃)₂Cl₂] (both Cl⁻ on the same side).
• Trans-[Pt(NH₃)₂Cl₂] (Cl⁻ on opposite sides).

What is an example of optical isomerism?

[Co(en)₃]³⁺ exists as two non-superimposable mirror images, d- and l-forms.

How does Valence Bond Theory (VBT) explain coordination compounds?

Metal hybridizes its orbitals (e.g., d²sp³ or sp³d²) to accommodate ligands.

• Explains magnetic properties (unpaired electrons).
• Example: [Co(NH₃)₆]³⁺ → d²sp³ hybridization, inner orbital complex (low spin, diamagnetic).

What is the Crystal Field Splitting (CFT) pattern for an octahedral complex?

Higher energy orbitals (e_g): d(x²-y²), d(z²)
Lower energy orbitals (t₂g): dxy, dxz, dyz
The energy difference between them is Δ₀.

Why is [NiCl₄]²⁻ paramagnetic but [Ni(CN)₄]²⁻ is diamagnetic?

• Cl⁻ is a weak ligand → High-spin → Unpaired electrons (paramagnetic).
• CN⁻ is a strong ligand → Low-spin → Paired electrons (diamagnetic).

Why does [Ti(H₂O)₆]³⁺ appear violet?

• Absorbs blue-green light.
• The complementary color (violet) is observed.

Arrange the ligands in increasing crystal field splitting strength (spectrochemical series).

I⁻ < Br⁻ < SCN⁻ < Cl⁻ < F⁻ < H₂O < NH₃ < en < CN^- < CO

• Weak field ligands (left) → Small splitting → High-spin complexes.
• Strong field ligands (right) → Large splitting → Low-spin complexes.

How is EDTA used in water treatment?

It chelates Ca²⁺ and Mg²⁺ ions, removing hardness from water.

What is the role of coordination compounds in medicine?

Cisplatin: Cancer treatment.

EDTA: Treats lead poisoning by forming stable metal complexes.

Name an important biological coordination compound.

Hemoglobin: Fe²⁺ complex that transports oxygen in blood.