Cobalt(III) Complexes and Werner's Theory

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Questions and Answers

Which metal ions have two vacant d orbitals available for octahedral hybridisation?

Co (d7)

Cr (d4)

Ti (d3) (correct)

Fe (d6)

What is the general effect of having more than three 3d electrons on octahedral hybridisation?

Two pairs of unpaired 3d electrons are always available.

Pairing of 3d electrons occurs to create a vacant pair of d orbitals. (correct)

It prevents any hybridisation from occurring.

It increases the magnetic moment of the compound.

Which coordination compound of manganese shows a magnetic moment corresponding to two unpaired electrons?

[MnO4]–

[Mn(CO)6]3–

[Mn(CN)6]3– (correct)

[MnCl6]3–

Which coordination compound of iron has a magnetic moment of a single unpaired electron?

[Fe(CN)6]3– Signup and view all the answers

Why do compounds containing d4 and d5 ions present complications in magnetic behavior?

Their pairing results in unexpected magnetic moments. Signup and view all the answers

What is the magnetic characteristic of [Co(C2O4)3]?

It is diamagnetic. Signup and view all the answers

How many unpaired electrons are found in [FeF6]3–?

Five unpaired electrons Signup and view all the answers

What phenomenon causes the differences in magnetic moments among compounds of the same metal ion?

Differences in crystal field splitting Signup and view all the answers

What is the color of the complex [Co(NH3)6]3Cl?

Yellow Signup and view all the answers

Which of the following complexes corresponds to a 1:3 electrolyte?

[Co(NH3)6]3Cl Signup and view all the answers

What term describes compounds like [CoCl2(NH3)4]Cl that have identical empirical formulas but distinct properties?

Isomers Signup and view all the answers

According to Werner's theory, what type of valences are satisfied by negative ions?

Primary valences Signup and view all the answers

Which geometric shapes are mentioned as common in coordination compounds of transition metals?

Octahedral, Tetrahedral, Square planar Signup and view all the answers

What does the coordination number refer to in coordination compounds?

The total number of ligands attached to the metal Signup and view all the answers

Which complex is correctly matched with its empirical formula?

[CoCl2(NH3)4]Cl - CoCl3.4NH3 Signup and view all the answers

What is the solution conductivity of the complex [CoCl(NH3)5]2Cl?

1:2 electrolyte Signup and view all the answers

What color is observed for the coordination entity [CoCl(NH3)5] when it absorbs yellow light?

Violet Signup and view all the answers

For the coordination entity [Co(NH3)5(H2O)]3+, which color is observed?

Red Signup and view all the answers

What is the role of the absorbed wavelength in determining the color of coordination entities?

It determines the complementary color observed Signup and view all the answers

Which color is absorbed by the coordination compound [Cu(H2O)4]2+?

Red Signup and view all the answers

In the context of crystal field theory, what happens when light corresponding to the blue-green region is absorbed by [Ti(H2O)6]3+?

The electron is excited from t2g level to eg level Signup and view all the answers

Which of the following coordination entities appears pale yellow?

[Co(CN)6]3- Signup and view all the answers

What is the next higher energy state for the electron in [Ti(H2O)6]3+ after the t2g level?

eg level Signup and view all the answers

Which of the following coordination entities absorbs light in the ultraviolet region?

[Co(CN)6]3- Signup and view all the answers

What does crystal field theory primarily consider the metal-ligand bond to be?

Ionic arising from electrostatic interactions Signup and view all the answers

What happens to the d orbitals in an isolated gaseous metal atom/ion?

They become degenerate and remain at the same energy Signup and view all the answers

In an octahedral coordination, which d orbitals experience more repulsion from ligands?

d x2 - y2 and d z2 Signup and view all the answers

What is the outcome when the degeneracy of d orbitals is lifted in crystal field theory?

The d orbitals split into different energy levels Signup and view all the answers

What type of splitting occurs in a crystal field with octahedral coordination?

Asymmetrical splitting due to ligand arrangement Signup and view all the answers

How does the presence of ligands affect the energy levels of d orbitals?

They raise the energy of orbitals aligned with the ligands and lower others Signup and view all the answers

Which statement regarding ligands is accurate in the context of crystal field theory?

Ligands are treated as negative charges or point dipoles Signup and view all the answers

What does crystal field theory fail to predict accurately for 4-coordinate complexes?

Structure predictions for tetrahedral and square planar complexes Signup and view all the answers

What geometry does tetracarbonylnickel(0) exhibit?

Tetrahedral Signup and view all the answers

Which of the following homoleptic carbonyls has a trigonal bipyramidal geometry?

Pentacarbonyliron(0) Signup and view all the answers

What kind of bond is present in octacarbonyldicobalt(0) that connects two cobalt atoms?

Metal-metal bond Signup and view all the answers

The structure of hexacarbonyl chromium(0) is categorized as which of the following?

Octahedral Signup and view all the answers

What is the primary type of bonding in metal carbonyls?

Covalent bonding Signup and view all the answers

What type of bonds do the metal-carbon bonds in metal carbonyls possess?

Both s and p character Signup and view all the answers

What connects the two square pyramidal units in decacarbonyldimanganese(0)?

M–M bond Signup and view all the answers

Which statement is true regarding the formation of the M–C s bond in metal carbonyls?

It is formed by the donation of lone pair electrons from carbonyl carbon. Signup and view all the answers

Study Notes

Cobalt(III) Chloride-Ammonia Complexes

There are four stable cobalt(III) chloride-ammonia complexes with different colours and conductivities.
The colour and conductivity of the complexes are determined by the number of chloride ions outside the coordination sphere.
Yellow [Co(NH3)6]3+ 3Cl- is a 1:3 electrolyte, meaning it dissociates into four ions in solution.
Purple [CoCl(NH3)5]2+ 2Cl- is a 1:2 electrolyte, meaning it dissociates into three ions in solution.
Green [CoCl2(NH3)4] + Cl- is a 1:1 electrolyte, meaning it dissociates into two ions in solution.
Violet [CoCl2(NH3)4] + Cl- is a 1:1 electrolyte, meaning it dissociates into two ions in solution.
The green and violet complexes have the same empirical formula, CoCl3.4NH3, but different properties, making them isomers.

Werner's Theory of Coordination Compounds

Werner's theory explains the bonding and structure of coordination compounds.
It describes two types of valences: primary and secondary.
Primary valences are ionizable and satisfied by negative ions, while secondary valences are non-ionizable and satisfied by neutral molecules or negative ions.
Secondary valence equals the coordination number and is fixed for a specific metal.
Ions/groups bound by secondary linkages to the metal have specific spatial arrangements called coordination polyhedra.
Coordination entities or complexes are enclosed in square brackets, while ions outside the brackets are counter ions.
Common coordination polyhedra in transition metal complexes include octahedral, tetrahedral, and square planar.

Magnetic Properties of Coordination Compounds

The magnetic properties of coordination compounds are determined by the number of unpaired electrons in the metal ion.
Coordination compounds with up to three d electrons have two vacant d orbitals for octahedral hybridisation, resulting in similar magnetic behaviour to their free metal ions.
When more than three d electrons are present, pairing of d electrons is required for octahedral hybridisation, influencing magnetic behaviour.
Magnetic data generally agrees with maximum spin pairing, especially for d6 complexes.
Exceptions exist for d4 and d5 complexes. For example, [Mn(CN)6]3- has two unpaired electrons while [MnCl6]3- has four unpaired electrons.
Werner's theory has limitations, failing to predict tetrahedral and square planar structures for four-coordinate complexes and to distinguish between weak and strong ligands.

Crystal Field Theory

Crystal Field Theory (CFT) explains bonding and structure of coordination compounds using an electrostatic model.
CFT considers the metal-ligand bond as purely ionic, arising from electrostatic interactions between the metal ion and ligands.
Ligands are treated as point charges for anions or point dipoles for neutral molecules.
In an isolated metal atom/ion, all five d orbitals are degenerate (have the same energy).
This degeneracy is lifted when a non-spherical field of negative charges from ligands surrounds the metal atom/ion.
The splitting pattern of d orbitals depends on the crystal field.
In octahedral coordination entities, ligands cause repulsion with metal d orbitals, leading to energy splitting.
d x2-y2 and d z2 orbitals, pointing towards ligands, experience greater repulsion and are raised in energy.
dxy, dyz, and dxz orbitals, directed between axes, are lowered in energy.

Colour of Coordination Compounds

The colour of coordination compounds is explained by CFT and relates to the absorption of specific wavelengths of light.
The colour observed is the complementary colour of the absorbed light.
For example, [Ti(H2O)6]3+ appears violet because it absorbs blue-green light.
Light absorption excites an electron from a lower energy level (t2g) to a higher energy level (eg).

Metal Carbonyls

Homoleptic carbonyls are compounds containing only carbonyl ligands and form readily with most transition metals.
They exhibit well-defined structures such as tetrahedral, trigonal bipyramidal, and octahedral.
Examples include:
- Tetracarbonylnickel(0) - tetrahedral
- Pentacarbonyliron(0) - trigonal bipyramidal
- Hexacarbonyl chromium(0) - octahedral
- Decacarbonyldimanganese(0) - two square pyramidal units joined by a Mn-Mn bond
- Octacarbonyldicobalt(0) - Co-Co bond bridged by two CO groups
The metal-carbon bond in metal carbonyls has both σ and π character.
The σ bond is formed by donation of the lone pair from the carbonyl carbon to a vacant metal orbital.

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Description

Explore the fascinating world of cobalt(III) chloride-ammonia complexes through this quiz. Learn about their colors, conductivities, and the principles underlying Werner's theory of coordination compounds. Test your understanding of this important topic in coordination chemistry.